Transcript RJR P2 Revision slides - abbreviated

P2
LO: calculate the forces acting on an object
Forces between objects
When two objects push or pull on each other, they exert
equal and opposite forces on one another e.g. you are
all pushing down on the floor, but the floor is also
pushing up on you….if it didn’t you’d fall straight
through the floor!
LO: calculate the forces acting on an object
Resultant force
If you have multiple forces acting on an object, you can
replace them with one single force that has the effect of
all the other forces combined together. This single force
is called the resultant force
LO: calculate the forces acting on an object
Calculating the resultant
A rocket produces a thrust of 2000N.
It has a weight of 1000N. What is the
resultant force acting on the rocket?
LO: calculate the forces acting on an object
Calculating the resultant
A rocket producing a resultant force of
1000N hits a wall, causing it to come to a
stop. What force does the wall exert on the
rocket and the rocket exert on the wall.
Explain the reasoning for your answer.
LO: calculate the forces acting on an object
Calculating the resultant
A car of weight 5000N produces a driving
force of 2000N. It experiences friction force
from the ground of 500N and air resistance
of 300N. What are the horizontal and
vertical resultant forces acting on the car?
LO: calculate the forces acting on an object
Rules for calculating the resultant
1. Forces that act in the same direction can be
added together
2. Forces that act opposite to each other must be
taken away
3. Forces that act vertically and horizontally CAN
NOT be added and taken away from each other
and MUST be considered separately.
LO: calculate the forces acting on an object
Effects of forces 1
• The resultant force on a stationary (not moving)
object is zero!
• If a resultant force is applied to an object, it will
accelerate in the direction of the force
LO: calculate the forces acting on an object
Effects of forces 2
• If an object is moving with constant speed, the
resultant force on it is zero
• If a resultant force is applied to a moving object,
it will accelerate in the direction of the force
LO: calculate the forces acting on an object
Calculating forces
F=mxa
• F = force (N)
• m = mass (kg)
• a = acceleration (m/s2)
F
mxa
LO: calculate the forces acting on an object
Example 1
A car of mass 400kg is accelerating at 5m/s2. What is the driving
force produced by the engine?
LO: calculate the forces acting on an object
Example 2
A novice skier is being pulled along a horizontal section of a nursery
slope. Given that her acceleration of 1.3m/s2 is provided by a force
of 70N, calculate her mass.
LO: calculate the forces acting on an object
Example 3
A man pushes a car with a force of 200N along a straight horizontal
road. He manages to accelerate the car by 0.1m/s². Find the mass of
the car.
LO: understand how to draw and interpret graphs of motion
Graphs of motion
Graphs of motion are a
visual representation of
the motion of a body
They can either show the
change in displacement or
change in velocity of an
object
LO: understand how to draw and interpret graphs of motion
Can you draw…
Mr R cycles into work. The
journey takes him 15 minutes
(900s) and is a total distance of
3km (3000m). We will try to
represent his journey using a
graph…
LO: understand how to draw and interpret graphs of motion
Can you draw…
1. Mr R cycles to the first traffic light, a
distance of 500m away. It takes him 180
seconds to do this.
2. He waits at the traffic lights for 120
seconds while the light is red
3. When the light turns green, he cycles
for 2000m without stopping. This takes
him 5 minutes to do.
4. After 2000m, Mr R has to stop at
another traffic light. He waits for 180
seconds.
5. Realising that he is about to be late, he
sprints the last 500m in 120 seconds.
LO: understand how to draw and interpret graphs of motion
Mini-plenary
1. Usain Bolt ran the 100m race in London 2012 in
approximately 9.6 seconds. He ran the first 20m in
approximately 2.7 seconds after accelerating and running
the final 80m in 6.9 seconds. It took him 20 metres to
come to a stop, which he covered in 5 seconds. Draw a
distance-time graph to show this journey.
2. Explain what a horizontal line on a distance-time graph
represents
Extension:
What do you think the steepness of a line on a distance-time
graph represents?
LO: understand how to draw and interpret graphs of motion
Using distance-time graphs
•
•
•
How steep the line is (the gradient) on a distance-time
graph tells you the speed that an object is moving
The steeper the line, the faster something is moving
Speed is measured in m/s
LO: understand how to draw and interpret graphs of motion
Calculating the gradient
Gradient =
Change in y
Change in x
Gradient =
∆y
∆x
Lets have a go at working out the speed that Mr C
was travelling at during his journey to school!
LO: understand how to draw and interpret graphs of motion
One last definition
Two cars are travelling on a road in
opposite directions. One is travelling
east at 20m/s and the other is
travelling west at 20m/s. Their speeds
are exactly the same.
However, their velocity’s are
different. What do you think their
velocity’s are?
Velocity is the speed of an object in a given direction. Two
objects can have the same speed, but very different
velocities
LO: understand how to draw and interpret graphs of motion
Can you draw…
Mr R has brought himself a slick
new ride! He has also moved
house and is now living in the
leafy suburbs. His journey takes
him 1200 seconds, his top speed
is 50m/s and his lowest is -30m/s.
Let’s plot his journey into school
on a velocity-time graph…
LO: understand how to draw and interpret graphs of motion
Can you draw…
1.
2.
3.
4.
5.
6.
Mr R leaves his house. He is happily driving
along on country roads at a steady speed of
30m/s for two minutes…
D’oh! He’s forgotten his lunch. He turns
round and drives back at 30m/s for two
minutes. He is at home for 60s.
Back on the road, Mr R drives at 30m/s for
300s
Now on the motorway, Mr R is able to drive
at 50m/s, which he does for 5mins
Coming off the motorway, he stops at a
traffic light for 120s
Realising he is going to be late, he steadily
increases his speed for the next 180 seconds
from 0 to 50m/s. He arrives JUST on time!
LO: understand how to draw and interpret graphs of motion
Task
1. What does a horizontal line on a velocity-time graph
represent?
2. How do you know if an object has stopped by looking at
the velocity-time graph?
3. How can you tell if an object is accelerating using a
velocity time graph?
4. Draw the velocity-time graph for the following journey:
0-10s = 50m/s
10-25s = 0m/s
25-50s = 60m/s
50-80s = acceleration to 80m/s
LO: understand how to draw and interpret graphs of motion
Acceleration
Acceleration is the change in speed of a body over a given
amount of time
LO: understand how to draw and interpret graphs of motion
Acceleration
Acceleration can be calculated using the following equation:
Change in velocity
Acceleration =
Time taken
Final velocity – initial velocity
Acceleration =
a=
v-u
t
Time taken
•
•
•
•
a = acceleration (m/s2)
v = final velocity (m/s)
u = initial velocity (m/s)
t = time (s)
LO: understand how to draw and interpret graphs of motion
Example 1
A car accelerates from a velocity of 10m/s to a velocity of 25m/s in
15 seconds. What is the acceleration of the car?
LO: understand how to draw and interpret graphs of motion
Example 2
A runner starts at rest and accelerates to a top speed of 10m/s. If he
does this in 2 seconds, what is his acceleration?
LO: understand how to draw and interpret graphs of motion
Example 3
A train accelerates at 2m/s² for 30 seconds. If its initial velocity was
10m/s, calculate what the final velocity will be after 30 seconds.
LO: understand how to draw and interpret graphs of motion
Task
1. What is the acceleration of a car that starts at rest and reaches
a top speed of 50m/s in 25 seconds?
2. A plane starts at rest. It takes 8 seconds to take off and
accelerates at a constant rate of 10m/s². What is the final takeoff velocity of the aircraft?
3. A runner starting at rest reaches a speed of 11m/s in 2.2
seconds during the drive phase of his 100m sprint. What is his
acceleration during this phase? Assuming that his speed
remains constant for the rest of the race, sketch the velocitytime graph for his journey
4. A car accelerates at 5m/s² for 12 seconds, reaching a final
velocity of 80m/s. What was the car’s initial velocity before it
started accelerating?
LO: understand how to draw and interpret graphs of motion
How are they linked?
Gradient =
Change in y
Change in x
Gradient =
∆y
∆x
The gradient of a velocity time graph represent the
acceleration of an object!
Go back and calculate the acceleration of Mr C in the
final part of his journey
LO: understand the factors that affect the stopping distance of a car
Streamlining
Most of the resistance
forces that act on a car
are due to air resistance.
Streamlining a car will
increase the top speed,
even if the engine is giving
the same power output
LO: understand the factors that affect the stopping distance of a car
Stopping distance
The stopping distance of a car is the minimum distance
that a car can safely stop in
Stopping distance = thinking distance + braking distance
LO: understand the factors that affect the stopping distance of a car
Thinking distance
The thinking distance is the distance travelled by the
vehicle in the time it takes for the driver to react
alcohol
other drugs and some
medicines
distractions, such as
mobile phones
tiredness
speed
LO: understand the factors that affect the stopping distance of a car
Stopping distance
The stopping distance is the distance travelled by the
vehicle during the time the braking force acts
weather
condition of
tyres/brakes
condition of road
speed
LO: understand the factors that affect the stopping distance of a car
Typical stopping distances
What effect would factors such as drugs, alcohol, tiredness,
higher speed, adverse weather, poor road conditions or
worn out breaks have on these stopping distances?
LO: understand the factors that affect the stopping distance of a car
Braking force
Which of these would need the bigger force to stop if the
stopping distance remained the same? Why?
LO: understand the factors that affect the stopping distance of a car
QWC Practice
A local authority is worried about the number of road deaths
occurring in the area. They have imposed a ban on mobile phones
while driving, imposed a speed limit of 30mph and installed speed
cameras. Explain how the changes may lead to fewer people being
hit by cars.
5-6 marks criteria:
• Knowledge of accurate information appropriately contextualised
• Detailed understanding, supported by relevant evidence and
examples
• Answer is coherent and in an organised, logical sequence,
containing a wide range of appropriate or relevant specialist
terms used accurately
• The answer shows almost faultless spelling, punctuation and
grammar.
LO: understand what is meant by terminal velocity
What is happening?
The graph below shows the velocity-time profile for a skydiver falling through
the air. Discuss with the people on your pod what you think is happening and
why. Think about the forces that are involved at each stage
LO: understand what is meant by terminal velocity
Moving in a fluid
Let’s think about what happens
when an object moves through a
fluid by considering a skydiver
When the skydiver FIRST jumps out
of the aircraft, gravity causes him
to accelerate.
The acceleration is a constant so
the line on v-t graph will have an
unchanging steepness at the
beginning
LO: understand what is meant by terminal velocity
Moving in a fluid
As the speed of the skydiver
increases, the air resistance on him
increases.
The increased air resistance causes
his acceleration to decrease.
However, his velocity is still
increasing i.e. he’s speeding up
slower than before, but he’s NOT
slowing down.
LO: understand what is meant by terminal velocity
Moving in a fluid
After a certain amount of time, the
weight of the skydiver and the air
resistance on the skydiver will be
balanced.
At this point, the skydiver will be
moving at a constant velocity. This
is the MAXIMUM velocity it is
possible for him to move with and
is known as the TERMINAL
VELOCITY.
LO: understand what is meant by terminal velocity
Moving in a fluid
The process that we have just
considered is relevant for ANY object
that is moving in a fluid e.g. a car
driving along a road, a plane flying at
2000ft, a submarine underwater etc.
LO: understand what is meant by terminal velocity
Moving in a fluid
The factors that will
increase/decrease the terminal
velocity of an object are:
• The driving force that the object
can generate
• How streamlined the object is
• The fluid that the object is
travelling through
LO: understand what is meant by terminal velocity
Calculating weight
The weight of an object is the force
that acts on an object due to
gravity. It can be calculated using
the following equation:
W=mxg
W = weight (Newtons)
M = mass (kg)
g = gravitational field strength
(N/kg)
g has a value of 9.81 on earth
LO: understand the link between force and extension of an object
Changing shape
When a force is applied to an object, it may accelerate.
However, a second effect that the force may cause is a change
in shape of the object
LO: understand the link between force and extension of an object
Stretching objects
When an object is stretched, it
stores elastic potential energy.
Some objects are better at
storing this energy than others.
Which of the materials on your
pod is better at storing elastic
potential energy?
LO: understand the link between force and extension of an object
Material properties
Beyond a point, the
material will start to show
plastic behaviour.
Beyond the proportional limit, the
material shows plastic behaviour. The
extension is now much harder to predict
A small increase in force
will give a large increase
in extension. The
deformation will be
irreversible (the material
will not go back to the
original shape when the
force is taken away)
LO: understand the link between force and extension of an object
Real world application
Knowing how materials change
shape under force is essential to
most aspects of university.
The flexing of aircraft wings can
dramatically change the lift
generated. It also needs to be
within limits to make sure the
wings don’t break off!
LO: understand the link between force and extension of an object
Hooke’s Law
Hooke’s law states that:
The extension of an object
is directly proportional to
the force that is applied to
it provided that the limit of
proportionality is not
exceeded
LO: understand the link between force and extension of an object
Hooke’s Law
Hooke’s law can be written as:
F=kxe
•
•
•
F = Force (N)
k = spring constant (N/m)
e = extension (m)
LO: understand the link between force and extension of an object
Task
1. Calculate the spring constant for the spring that you did the
experiment with
2. A spring is loaded with a force of 50N four times. The spring
shows extensions of 0.23m, 0.25m, 0.25m and 0.24m. Calculate
the spring constant for this spring
3. For the spring in the question above, calculate the force when
the extension of the spring is 100cm.
4. A second spring is loaded with 100N. It shows an extension of
60cm. What is the difference between the spring constants of
the two springs?
5. What would be the force required to extend the second spring
by 0.45m?
LO: understand how energy can be transferred
What is work?
An object is said to have done WORK when it
transfers (uses) energy
LO: understand how energy can be transferred
Calculating work
The work done by an object is equal to the
amount of energy that it transfers
Work done = force x distance
W=fxd
• W = work done(J)
• f = force (N)
• d = distance(m)
LO: understand how energy can be transferred
Example 1
An object of weight 40N is raised by a height of 0.4m.
Calculate the work done in raising the object.
LO: understand how energy can be transferred
Example 2
2000J of energy is transferred by a sprinter as he runs a distance of
100m. Calculate the force that is exerted by the sprinter as he is
running.
LO: understand how energy can be transferred
Example Questions
1. What is the definition of work done?
2. What is the unit for energy?
3. The engine of a car exerts a force of 750N. How much energy
would be transferred by the engine if the car moved a distance
of 100m?
4. An object of weight 50N is raised by a height of 200cm. What is
the work done in raising the object?
5. 700J of energy is used by a person to move a distance of 10m.
What is the force exerted by the person as they walk the
distance?
6. Object A has a weight of 200N. Object B has a weight of 350N.
If 1000J of energy is used to raise each object, which object will
gain the most height?
LO: understand how energy can be transferred
Calculating power
Power is the amount of work done/energy
transferred in a given time
Power = work done / time
P=W/t
• P = power (W)
• W = work done (J)
• t = time (s)
LO: understand how energy can be transferred
Example 1
An object of weight 700N is raised by a height of 2m in a time
of four seconds. Calculate the work done in raising the object
and the power.
LO: understand how energy can be transferred
Example Questions
1. A car engine transfers 3000J in 20 seconds. What is the
power generated by the engine?
2. 400J of energy is transferred in raising an object in 1
minute. What is the power?
3. A kettle has a power rating of 2000W. How much work is
done by the kettle in boiling water in 40 seconds?
4. A student of weight 500N transfers 2000J whilst running
up some stairs. She reaches the top of the stairs in 3
seconds. How high are the stairs and what is her power?
5. A sprinter can generate 150W whilst running. If he
transfers 450J of energy, how long has he been running
for?
LO: understand the nature of gravitational potential energy
Gravitational Potential Energy
Any object that is raised
above the ground will
have gravitational
potential energy
LO: understand the nature of gravitational potential energy
Gravitational Potential Energy
GPE = mass x Gravitational x height
Field strength
GPE = m x g x h
•
•
•
•
GPE = gravitational potential
energy (J)
m = mass (kg)
g = gravitational field strength
(N/kg)
h = height (m)
LO: understand the nature of gravitational potential energy
Example 1
An object of mass 10kg is raised by a height of 20m. What is
the gravitational potential energy of the object?
LO: understand the nature of gravitational potential energy
Example 2
An object gains gravitational potential energy of 300J. If the
mass of the object is 3kg, what is the height that the object
has been raised?
LO: understand the nature of kinetic energy
Kinetic energy
All objects that are
moving have kinetic
energy!
LO: understand the nature of kinetic energy
Kinetic energy
KE = ½ x m x v²
•
•
•
KE = kinetic energy (J)
m = mass (kg)
v = velocity (m/s)
LO: understand the nature of kinetic energy
Example 1
An object has a mass of 2kg and is moving with a velocity of
5m/s. What is the kinetic energy of the object?
LO: understand the nature of kinetic energy
Example 2
An object of mass 300g has 600J of kinetic energy. How fast is
the object moving?
LO: understand the nature of kinetic energy
Example questions
1. What is the equation that is used to calculate the kinetic
energy of an object?
2. Calculate the kinetic energy of an object of mass 500g
that is moving with a velocity of 20m/s
3. A car of mass 500kg is a moving with a velocity of 10m/s.
It accelerates to a velocity of 15m/s. What is the KE of the
object before and after it accelerates?
4. A sprinter has kinetic energy of 1000J and a mass of 68kg.
How fast is the sprinter running?
5. A ball of mass of 0.5kg is dropped from a height of 2m.
Assuming that all of the GPE is transferred to KE, what
will be the velocity of the ball when it hits the ground?
LO: understand what is meant by momentum
Momentum
ALL MOVING
OBJECTS HAVE
MOMENTUM!
LO: understand what is meant by momentum
Momentum
P=mxv
• P = momentum (kgm/s)
• m = mass (kg)
• v = velocity (m/s)
LO: understand what is meant by momentum
Example question 1
An object of mass 300g is moving with velocity of 5m/s. What
is its momentum?
LO: understand what is meant by momentum
Example question 2
An object has momentum of 50kgm/s. If the object has a
mass of 25kg, what is its velocity?
LO: understand what is meant by momentum
Example questions
1. What is the momentum of a bullet of mass 50g travelling at
300 m/s?
2. What is the momentum of a dog (mass 12 kg) fired out of a
canon at 120 m/s?
3. Calculate the momentum of a 65 kg sprinter when
travelling at 9.5 ms-1.
4. Calculate the velocity of a car of mass 700 kg that has the
same momentum as the sprinter in Q3
5. A body has a mass of 2.5 kg. Calculate:
• Its momentum when it has a velocity of 3.0 m/s
• Its velocity when it has a momentum of 10.0 kgm/s
LO: understand what is meant by momentum
Conservation of momentum
In a closed system, the total
momentum before an event and
the total momentum after an event
are the same. This is called
conservation of momentum.
Events you may be asked about in
your exams are:
• Collisions
• Explosions
LO: understand what is meant by momentum
Example 1
A railway engine of mass 800kg travelling at 5m/s collides with and
becomes attached to a truck of mass 200kg travelling at 2m/s.
Calculate the speed of the truck and engine after the collision
LO: understand what is meant by momentum
Example 2
A 0.5kg trolley is pushed at a velocity of 1.2m/s into a stationary
trolley of mass 1.5kg. The two trolleys stick to each other after the
impact. Calculate:
• The momentum of the 0.5kg trolley before the collision
• The velocity of the two trolleys straight after the impact
LO: explain how safety features on a car work
Brakes and crumple zones
Brakes and crumple zones are two of the main safety
features on a car
LO: explain how safety features on a car work
Brakes and crumple zones
Both features work by transferring kinetic energy into other
forms. What energy transfers take place in each of these
features?
LO: understand static electricity
Structure of an atom
All matter is made up of
atoms
However, an atoms is NOT
the smallest unit of matter
like you might have been
previously taught
Atoms of themselves made
of smaller particles
LO: understand static electricity
What is an atom made up of?
Protons – Positively charged
particles found inside the
nucleus
Neutrons – Neutral particles
found inside the nucleus
Electrons – Negatively
charged particles that orbit
the nucleus
LO: understand static electricity
Static electricity by friction
When you rub one of the rods with the cloths, you
create static electricity. This happens in one of two
ways.
For the polythene rod, the dry cloth transfers electrons
TO the surface of the rod and gives it a negative charge
LO: understand static electricity
Static electricity by friction
When you rub one of the rods with the cloths, you
create static electricity. This happens in one of two
ways.
For the perspex rod, the dry cloth transfers electrons
away from the surface of the rod. This gives it a
positive charge
LO: understand static electricity
Static electricity rules
1. Like (The same) charges attract
2. Unlike (The opposite) charges repel
LO: Understand how to create electrical circuits
Key definitions
When considering electricity, we will usually use three key
terms:
1) Current: This is the flow of electric charges around a
circuit. The size of the current is dependent on the rate of
flow of electric charges
2) Potential Difference (Voltage): The potential difference
between two points is the work done per unit charge
between two points
3) Resistance: This is the resistance to the flow of electrons
around a circuit
LO: Understand how to create electrical circuits
Calculating current
I = Q/t
• I = Current (Amps, A)
• Q = Charge (Coulombs, c)
• t = Time (s)
LO: Understand how to create electrical circuits
Example question 1
Calculate the current when 4C passes a point in 8
seconds
LO: Understand how to create electrical circuits
Example question 2
An ammeter is records a current of 8A. Calculate
how much charge is passing through the ammeter in
10 seconds.
LO: Understand how to create electrical circuits
Task
1. What is the current when 20C of charge pass through an
ammeter in 2minutes?
2. A battery can produce 20A of current. How much charge
does it discharge in 30s?
3. Another battery can produce a charge of 30A. How long
will this battery be running before it has discharge the
same amount of charge as the battery in Q2?
4. A car engine requires a battery that can produce a
current of 40A to start. A mechanic places a battery that
can discharge 100C in 30s into a car. Will this battery be
good enough to start the car? Why?
5. For the question above, how much charge would the
battery have to discharge in 30s to start the engine?
LO: Understand how to create electrical circuits
Calculating voltage
V = W/Q
• V = Voltage (Volts, V)
• W = Work done (Joules, J)
• Q = Charge (Coulombs, c)
LO: Understand how to create electrical circuits
Example question 1
A battery transfers 30J for every coulomb of charge
that passes through the battery. What is the
potential difference of the battery?
LO: Understand how to create electrical circuits
Example question 2
A battery has a voltage rating of 40V. How much
energy is transferred by the battery if 20C of charge
pass through the battery?
LO: Understand how to create electrical circuits
Task
1. What is the voltage of a battery if it transfers 40J of
energy for every 10C that pass through it?
2. A builder requires a 400V battery to power his
pneumatic drill. He is told that a battery transfers 1000J
for every 3C of charge that pass through it. Will this
battery be good enough? Why?
3. How much energy would the battery in the question
above need to transfer for every 3C to have a voltage of
400V?
4. Battery A has a rating of 300V. Battery B has a rating of
500V. What is the difference in the amount of work done
by the two batteries if 20C of charge pass through both
batteries?
LO: Understand how to create electrical circuits
Circuit symbols
LO: Understand the relationship-between current and voltage in a circuit
Ohm’s Law
Ohm’s Law states that the
current through a resistor is
proportional to the potential
difference provided the
temperature is constant
LO: Understand the relationship-between current and voltage in a circuit
Ohm’s Law
V = IR
• V = Voltage (V)
• I = Current (A)
• R = Resistance
(Ohms, Ω)
LO: Understand the relationship-between current and voltage in a circuit
Ohm’s Law 1
Calculate the potential difference across a 4Ω resistor
when the current through it is 10A.
LO: Understand the relationship-between current and voltage in a circuit
Ohm’s Law 2
The potential difference across a 30Ω is 20V. What is the
current through the resistor?
LO: Understand the relationship-between current and voltage in a circuit
Task
Calculate:
1. The resistance of a bulb if the current is 0.5 A and the
potential difference across the bulb is 2 V.
2. The potential difference across a bulb if the resistance
of the bulb is 3  and the current flowing is 2 A
3. The potential difference across a resistor of 5  with
a current of 1.5 A.
4. The total resistance of a circuit if the potential
difference across the cell is 12V and the current is 3 A.
5. The current flowing in a circuit with a total resistance
of 5  and a potential difference across the cell of 6V.
LO: Understand the relationship-between current and voltage in a circuit
Non-Ohmic Components1
An LED does not follow
Ohm’s law and is
designed to only allow
current to flow through in
one direction
LO: Understand the relationship-between current and voltage in a circuit
Non-Ohmic Components2
An LED does not follow
Ohm’s law and will only
light up when current to
flows through in the right
direction.
If current tries to flow in
the other direction it
encounters a MAHOOSIVE
resistance!
LO: Understand the relationship-between current and voltage in a circuit
Non-Ohmic Components2
An LDR is a component
whose resistance
decreases as the light
intensity that falls on it
increases
Where would this be
useful?
LO: Understand the relationship-between current and voltage in a circuit
Non-Ohmic Components3
A thermistor is a component whose resistance
decreases when the temperature increases.
Where would this be useful?
LO: describe features of mains electricity
AC vs DC
If you turn on any battery
powered device the
electricity will only ever
flow in one direction.
This is called DIRECT
CURRRENT (d.c.) as the
electricity goes around in
just one direction.
LO: describe features of mains electricity
AC vs DC
However, the same isn’t
true for mains electricity.
Mains electricity uses
ALTERNATING CURRENT
(a.c.) which repeatedly
flows in one direction and
then reverses its flow. The
frequency is how many
times it changes direction
in one second
LO: describe features of mains electricity
Key points
1. Mains electricity uses
a.c.
2. Mains electricity is at
230V
3. Mains electricity has a
frequency of 50Hz. This
means it changes
direction 50 times in
one second
LO: describe features of mains electricity
Cables and Plugs
Cables and wires are
designed to allow people to
use them without risk of
hurting themselves. Most
appliances are supplied with
three-core cable. This means
the cable is made up of three
separate wires.
LO: describe features of mains electricity
Components of a plug and cable
1) Live wire (brown) – This
carries the current to the
appliance. Touching this can
be deadly!
2) Neutral wire (blue) – This
completes the circuit and is
usually at 0V
3) Earth wire (green/yellow) –
This ‘earths’ the appliance in
case one of the wires touches
the casing
4) Fuse – This stops the flow of
current if it gets too high
LO: describe features of mains electricity
Earthing
Components are earthed to make
sure you don’t get an electric
shock if the live wire accidentally
touches the casing. The electricity
will flow harmlessly through the
earth wire instead of through you
when you touch the casing.
However, appliances with plastic
cases (hairdryers etc.) don’t have
earth wires. Why is this?
LO: describe features of mains electricity
Earthing
Plastic is an insulator, so there is
no danger if the live wire touches
the casing. Therefore, these
appliances are supplied with twocore cables instead of three-core
cables i.e. they don’t have earth
wires because they don’t need
them
LO: describe features of mains electricity
Fuses
A fuse is a component that
has a wire running through
it made of a different
material/thickness than the
rest of the circuit. It is
designed to stop current
that is too high flowing
through it.
LO: describe features of mains electricity
Fuses
Fuses have a rating based on the
amount of current they will allow
through. For example, a 13A fuse
will allow a maximum of 13 amps
of current to flow through. If
MORE than this tries to flow
through, the wire heats up and
melts, breaking the circuit and
protecting the appliance
LO: describe features of mains electricity
Circuit Breakers
Circuit breakers are fitted in
newer homes. They measure the
difference in current in the live
and neutral wires. If the
difference is too great, an
electromagnetic switch opens
(‘trips’) which stops the flow of
current. They work a lot faster
than fuses and can be reset easily
LO: describe features of mains electricity
Circuit Breakers
Use the textbook spread to create a poster on fuses and
circuit breakers. Your poster to include details of how they
work and advantages and disadvantages of both
LO: describe features of mains electricity
Knowledge check
Copy the true sentences and change the false sentences to
make them true:
1. The earth wire in a three-core cable is usually brown
2. Appliances with metal casings are supplied with threecore cables
3. Fuses stop current flowing through a circuit by melting
when the current flowing through them is above a
certain value
4. A circuit breaker works by monitoring the difference in
current between the live and earth wire
5. Mains electricity uses direct current at 100Hz.
LO: describe features of mains electricity
QWC Practice
Using as much detail as possible, explain how fuses and
circuit breakers work to protect people and appliances.
Which, in your opinion, is the better choice for installation
into a home and why?
5-6 marks criteria:
• Knowledge of accurate information appropriately contextualised
• Detailed understanding, supported by relevant evidence and
examples
• Answer is coherent and in an organised, logical sequence,
containing a wide range of appropriate or relevant specialist
terms used accurately
• The answer shows almost faultless spelling, punctuation and
grammar.
LO: describe features of mains electricity
Calculating power
P=VxI
• P = Power (w)
• V = Voltage (V)
• I = Current (A)
LO: describe features of mains electricity
Example 1
Calculate the power of a bulb if it is supplied with a potential
difference of 230V and the current flowing through it is 0.4A
LO: describe features of mains electricity
Example 2
A kettle has a power rating of 1000W. If it is supplied with a
potential difference of 230V, what is the current flowing
through it?
LO: describe features of mains electricity
Example questions
1. A light bulb is connected to a 2V supply and experiences a
current of 6.4A. What is the power rating of the bulb?
2. A kettle has a power rating of 1500w. What is the potential
difference that it must be supplied with to have a current
flowing through it of 30A?
3. A student attaches a 10V supply to a bulb with a power rating
of 100w. What is the current running through the bulb?
4. The student now connect a 25w bulb to the same supply.
What is the difference between the current going through
this bulb compared to the 100w bulb?
5. Bulb A transfers 1000J in 10seconds. Bulb B transfers 1500J
in 3 seconds. Which bulb will have a higher current running
through it when connected to a 12V supply?
LO: Understand how to create electrical circuits
Calculating energy
E=VxQ
• E = Energy transferred (Joules, J)
• V = Voltage (Volts, V)
• Q = Charge (Coulombs, c)
LO: Understand how to create electrical circuits
Example question 1
A battery transfers 30J for every coulomb of charge
that passes through the battery. What is the
potential difference of the battery?
LO: Understand how to create electrical circuits
Example question 2
A battery has a voltage rating of 40V. How much
energy is transferred by the battery if 20C of charge
pass through the battery?
LO: Understand how to create electrical circuits
Task
1. What is the voltage of a battery if it transfers 40J of
energy for every 10C that pass through it?
2. A builder requires a 400V battery to power his
pneumatic drill. He is told that a battery transfers 1000J
for every 3C of charge that pass through it. Will this
battery be good enough? Why?
3. How much energy would the battery in the question
above need to transfer for every 3C to have a voltage of
400V?
4. Battery A has a rating of 300V. Battery B has a rating of
500V. What is the difference in the amount of work done
by the two batteries if 20C of charge pass through both
batteries?
LO: understand the nature of radioactive decay
What is an atom made up of?
Protons – Positively charged
particles found inside the
nucleus
Neutrons – Neutral particles
found inside the nucleus
Electrons – Negatively
charged particles that orbit
the nucleus
LO: understand the nature of radioactive decay
Protons, neutrons and electrons
Particle
Proton
Neutron
Electron
Relative charge
+1
0
-1
Relative mass
1
1
1/2000
LO: understand the nature of radioactive decay
Relative sizes
LO: understand the nature of radioactive decay
Atomic and Mass number
Atomic number: This is the number of protons inside the
nucleus of an atom
WARNING: Even though the number of protons and electrons
in a neutral atom are the same, make sure you say the
correct definitions if you are asked in an exam!
Mass number: This is the number of protons + neutrons in
the nucleus of an atom
LO: understand the nature of radioactive decay
Atomic and Mass number
Atomic number: This is the number of protons inside the
nucleus of an atom
Mass number: This is the number of protons + neutrons in
the nucleus of an atom
LO: understand the nature of radioactive decay
Example 1
Calculate the following quantities for the element below
(i) Atomic number
(ii) Mass number
(iii) Number of protons
(iv) Number of electrons
(v) Number of neutrons
LO: understand the nature of radioactive decay
Example 2
Calculate the following quantities for the element below
(i) Atomic number
(ii) Mass number
(iii) Number of protons
LO: understand the nature of radioactive decay
Task
Use your periodic table to find the following quantities
for: nitrogen, oxygen, iron, platinum, gold, lead,
mercury, potassium, calcium, phosphorus, argon, xenon
(i) Atomic number
(ii) Mass number
(iii) Number of protons
(iv) Number of electrons
(v) Number of neutrons
If the numbers are decimals, round them to the nearest
whole number
LO: understand the nature of radioactive decay
The Plum Pudding Model - 1897
LO: understand the nature of radioactive decay
Enter Rutherford
Ernest Rutherford fired alpha particles at gold foil.
Alpha particles have a positive charge and he
expected them to go through the particle, with a
small amount of deviation from their path
LO: understand the nature of radioactive decay
Gold Foil Experiment - 1911
The results are very different!
Most alpha particles go straight through with no
deviation! Some, however, are diverted through very
large angles! The physics community is flummoxed by
this finding!
LO: understand the nature of radioactive decay
Gold Foil Experiment - 1911
The results are very different!
Most alpha particles go straight through with no
deviation! Some, however, are diverted through very
large angles! The physics community is flummoxed by
this finding!
LO: understand the nature of radioactive decay
Conclusions
Most of the fast, highly charged
alpha particles went whizzing
straight through undeflected.
SUGGESTS THAT MOST OF THE
ATOM IS EMPTY SPACE!!
LO: understand the nature of radioactive decay
Conclusions
Some of the alpha particles were
deflected back through large angles.
A very small number of alpha
particles were deflected backwards!
SUGGESTS THAT THERE IS A
CONCENTRATED POSITIVE MASS
SOMEWHERE IN THE ATOM.
LO: understand the nature of radioactive decay
Conclusions
A very small number of alpha
particles were deflected backwards!
SUGGESTS THAT THE CONCENTRATED
MASS IS MINISCULE COMPARED TO
THE SIZE OF THE REST OF THE ATOM,
BUT CONTAINS MOST OF THE MASS
LO: understand the nature of radioactive decay
Types of Radiation
There are three different kinds of radiation. Each one has a
unique nature and penetration
Alpha radiation:
This particle is made up of two
protons and two neutrons (i.e. a
Helium nucleus). It has a charge
of +2 and moves slowly because
of it’s large mass. It can be
stopped by a few cm of air or by
a piece of paper
LO: understand the nature of radioactive decay
Types of Radiation
There are three different kinds of radiation. Each one has a
unique nature and penetration
Beta radiation:
During beta radiation, a neutron turns into
a proton inside the nucleus and gives off
an electron, which is fired from the
nucleus. The electron is small and light
and so moves very fast! Beta particles can
be stopped by a thin sheet of aluminium
LO: understand the nature of radioactive decay
Types of Radiation
There are three different kinds of radiation. Each one has a
unique nature and penetration
Gamma radiation:
Gamma radiation usually follows
alpha or beta decay. It is NOT a
particle like the other two. It is a high
energy EM wave that travels at the
speed of light (the fastest that
anything can travel Joel). It can only
be stopped by a very thick piece of
lead or concrete.
LO: understand the nature of fusion and fission
Isotopes
The diagram below shows three isotopes of
hydrogen. What is the same and different for each
isotope of hydrogen?
LO: understand the nature of fusion and fission
Isotopes
An isotope of an element has the same number of
protons and neutrons as the original, but a
different number of neutrons.
LO: understand the nature of fusion and fission
Radioactivity of a substance
LO: understand the nature of fusion and fission
Radioactivity of a substance
As a radioactive
substance decays, the
number of particles left
in it will start to reduce.
Therefore the
radioactivity of the
substance will begin to
decrease. It will
continue to decrease,
until the radioactivity
has reached zero!
LO: understand the nature of fusion and fission
Half-life
The half-life of a
substance is the time it
takes for HALF of the
particles in a sample to
decay or for the
radioactivity of a
substance to decrease
by HALF.
LO: understand the nature of fusion and fission
Half-life
What is the half life
of this substance?
LO: understand the nature of fusion and fission
Recap
Particle
Charge
Proton
+1
Neutron
0
Electron
-1
In each atom, the number
of protons will ALWAYS be
the same as the number
of electrons. This makes
sure that the overall
charge is zero.
LO: understand the nature of fusion and fission
Nuclear Fission
Nuclear fission is a process that uses
atoms to generate VAST amounts of
energy.
LO: understand the nature of fusion and fission
Nuclear Fission
To begin with, we have a
simple Uranium nucleus.
Uranium is used because it
is already unstable.
A slow moving neutron is
fired at the Uranium.
Neutron
Uranium
nucleus
LO: understand the nature of fusion and fission
Nuclear Fission
Neutron
Unstable
nucleus
Uranium
nucleus
The neutron
attaches itself
to the uranium
and makes it
even more
unstable!
LO: understand the nature of fusion and fission
Nuclear Fission
The unstable Uranium splits
into two smaller nuclei,
releasing energy in the process
Neutron
Unstable
nucleus
Uranium
nucleus
2 smaller nuclei
(e.g. barium and
krypton)
LO: understand the nature of fusion and fission
Nuclear Fission
Along with the energy, some
more neutrons are also
released!
Neutron
Unstable
nucleus
Uranium
nucleus
2 smaller nuclei
(e.g. barium and
krypton)
More
neutrons
LO: understand the nature of fusion and fission
Chain reactions
These fission reactions produce a
lot of energy and are used in
nuclear generators.
However, each fission reaction
produces more and more neutrons.
More
neutrons
LO: understand the nature of fusion and fission
Chain reactions
Each of the neutrons can cause
more fission reactions, releasing
more energy and more neutrons.
The reaction can soon become an
uncontrollable chain reaction,
and when that happens…
More
neutrons
LO: understand the nature of fusion and fission
Using fission
LO: understand the nature of fusion and fission
True or False?
Copy the true sentences and change the false sentences to
make them true
1) Nuclear fission uses fast-moving electrons
2) The most common fuel used in a nuclear reactor is uranium
3) Nuclear fission involves one nucleus splitting into smaller
nuclei and releasing energy in the process
4) An advantage of nuclear fission is that it doesn’t produce
any harmful radioactive waste
5) A chain reaction occurs when too many neutrons cause
fission reactions and the process can no longer be
controlled
LO: understand the nature of fusion and fission
Nuclear fusion
Although the names sound very similar,
fission and fusion are VERY DIFFERENT
PROCESSES.
LO: understand the nature of fusion and fission
Nuclear Fission
In fission, one nuclei is split
into smaller nuclei to release
energy!
Neutron
Unstable
nucleus
Uranium
nucleus
2 smaller nuclei
(e.g. barium and
krypton)
More
neutrons
LO: understand the nature of fusion and fission
Nuclear fusion
In nuclear fusion, two nuclei are fused
together to release energy. It is the
opposite of nuclear fission.
LO: understand the nature of fusion and fission
Where does this happen?
Contrary to
popular belief,
our sun is not a
massive fireball. It
is actually a
massive fusion
reactor!
LO: understand the nature of fusion and fission
Where does this happen?
The sun is made up of
mainly hydrogen. The
high temperature on
the sun allows the
hydrogen to fuse
together and make
helium, releasing
massive amounts of
energy in the process
LO: understand the nature of fusion and fission
Why don’t we use fusion?
Fusion seems like a
great process! We
only need hydrogen to
do it (which we can
get from water) and
make helium, which is
not a greenhouse
gas…so why are we
not using it?
LO: understand the nature of fusion and fission
Fusion future
Although fusion isn’t
economically viable
right now, it will
(probably!) be one of
the main ways we
generate energy in the
future. Lots and lots
of research is
currently being done
into it currently….
LO: understand the lifecycle of a star
Nebula
All stars start their
lives as part of a
nebula. Nebulae
are large clouds of
dust and gas
(mainly hydrogen).
LO: understand the lifecycle of a star
Protostar
Over millions of years,
gravity will cause the dust
and gas in the nebula to
come together. As it does
this, the temperature
increases until hydrogen can
fuse. When this happens, a
protostar is born. This is
kind of like a ‘baby’ star.
LO: understand the lifecycle of a star
Main sequence star
The main sequence star is
the next stage after a
protostar. Hydrogen fusion
is now in full flow and the
star is much hotter and
brighter than the protostar.
LO: understand the lifecycle of a star
Red Giant star
When a star runs out of
hydrogen, it begins to fuse
other, heavier elements.
This releases more energy,
causing the star to expand.
It also gives off red light,
giving it the name ‘Red
Giant’.
LO: understand the lifecycle of a star
White dwarf
When the red giant has run
out of all fuel and can fuse
nothing more, it will lose its
outer layers. This leaves just
the core, which is still
extremely hot. It is so hot it
glows white hot, giving the
name to this stage – the
‘white dwarf’.
LO: understand the lifecycle of a star
Black dwarf
After a long enough time,
the white dwarf will cool
down enough so that it
stops glowing white hot. It
is now called a ‘black
dwarf’.
LO: understand the lifecycle of a star
Task
The lifecycle that
you have just
covered is for
stars about the
same mass as our
sun…Heavier
stars, however,
lead a slightly
different life
LO: understand the lifecycle of a star
Red Super Giant star
Following the main
sequence, the star begins to
fuse together heavier
elements. However, as it
has far more fuel, it
expands to a much larger
size and gives off much
more energy.
LO: understand the lifecycle of a star
Supernova
For very heavy stars, once
they have run out of fuel,
the star begins to collapse
in on itself. It continues to
collapse until it reaches a
critical point when it can’t
collapse any more. This
causes a MASSIVE
shockwave!
LO: understand the lifecycle of a star
Supernova
The shockwave is so large
that the outer layers
EXPLODE outwards! The
explosion only lasts
seconds, but can release as
much energy in those
seconds as the star has
released up to that point! It
can be as bright as the light
from 10billion stars.
LO: understand the lifecycle of a star
Neutron star
After a supernova, only the
star’s core is left behind.
During the collapsing
process, this core is turned
into just neutrons.
The resulting ‘neutron star’
is very very dense. One
spoonful of a neutron star
would weigh more than the
Earth!
LO: understand the lifecycle of a star
Black hole
In some very very rare
cases, the core of a star left
over after a supernova will
continue to collapse. It will
keep getting smaller and
smaller until the whole star
has collapsed into an
infinitely small point.
LO: understand the lifecycle of a star
Black hole
This ‘singularity’ has an
immense gravitational
force. It’s attraction is so
strong that not even light
can escape from it. Hence
the name ‘black hole’.
LO: understand the lifecycle of a star
How elements are formed
Stars are the perfect place for
elements to be made! They
are like massive ovens that
have the energy needed to
make new elements
LO: understand the lifecycle of a star
Stage 1
When a star is ‘young’ it has
plenty of hydrogen. It fuses
the hydrogen together to form
helium. This releases massive
amounts of energy in the form
of light and heat.
But what happens when the
hydrogen runs out?
LO: understand the lifecycle of a star
Stage 2
When a star runs out of
hydrogen, it has massive
amounts of helium left. It has
no choice but to start fusing
helium, instead of hydrogen.
Fusing helium makes heavier
elements, like lithium and
beryllium.
LO: understand the lifecycle of a star
Stage 2
Fusing helium releases more
energy than fusing hydrogen.
This makes the star bigger and
it enters the red giant phase.
But what does it do when it
runs out of helium?
LO: understand the lifecycle of a star
Stage 3
When the star has run out of
helium, it will start fusing the
heavier elements that it has
created. This will make even
heavier elements, such as
Boron and Carbon.
LO: understand the lifecycle of a star
Stage 4
The star will keep on going
through this process of
running out of fuel and fusing
heavy elements that it has
created. This will make heavier
and heavier elements.
The heaviest element that
stars can make is Iron.
LO: understand the lifecycle of a star
What about elements heavier than Iron?
LO: understand the lifecycle of a star
Supernova
The temperature in stars is not
hot enough to make elements
heavier than Iron. For these
temperatures, a supernova is
required!