Transcript Energy:

Magnetism
Magnetism
• Magnetism – Forces
exerted by magnets
• Lodestones – rocks
that are naturally
magnetic
– Found in Magnesia in
Greece
– Used by Chinese to
navigate ships
Magnetic Poles
• Magnetic poles – one
of the regions on a
magnet that produces
magnetic forces
– Like poles repel
– Opposite poles attract
– Compass: end that
points northward is the
north seeking pole,
end that points
southward is the south
seeking pole
Magnetic Field
Magnetic field – the space • Shape of the field is
around a magnet, in which revealed by magnetic
a magnetic force is
field lines
exerted
Every spinning electron is a magnet, most atoms’ electrons spin in different directions
cancelling their magnetic force
Magnetic Field
Opposite poles
Similar poles
Choose words to fill in the blanks:
Electron
Field
force
Magnets
Magnetism is a force exerted by _______.
Magnets are objects surrounded by a
magnetic field. A magnetic ____ is the
space around a magnet, in which a
magnetic ____ is exerted. Every spinning
______is a magnet, most atoms’ electrons
spin in different directions cancelling their
magnetic force.
Choose words to fill in the blanks:
attract
poles
regions
repel
Each magnet has two ____, a north and a
south pole. The magnetic poles are one of
the ______ on a magnet that produces
magnetic forces. Like poles will ______
each other while opposite poles will ______
each other.
Electromagnetic Induction
Magnets moved near—or even
inside coils of wire induce
(cause) a current in the coil.
The more coils there are,
the more current there is.
Electromagnetic Induction
Moving wire and keeping the magnet
stationary is the same as moving the magnet
and keeping the wire stationary.
Faraday’s Law
The induced voltage in
a coil is proportional to
the product of the
number of loops and the
rate at which the
magnetic field changes
within those loops
Electromagnet
• A moving charge
produces a magnetic
field.
• An electric current
produces a magnetic
field
• Magnetic field around
a wire forms
concentric circles
Electromagnets
• A current-carrying coil of wire with many
loops is an electromagnet
Generators
Device that rotates a
coil of wire in a
stationary magnetic
field inducing a voltage
in the coil
Converts mechanical
energy into electrical
energy
Hand powered generator
Steam powered generator
Electric Motors
 A permanent magnet is
used to produce a
magnetic field in a region
where a loop of wire is
mounted so that it can
turn about an axis.
 Brushes – Parts of the
wire that brush against
contacts in a motor
 Armature – in larger
motors, many coils of wire
are wound about an iron
cylinder
Turbine
Generator, where the
armature is connected
externally to a wheel
The wheel may be
powered by wind,
falling water or steam
Steam powered generator
Motor Effect vs Generator Effect
• Motor effect – when
a current in a wire
moves
perpendicular to a
magnetic field, there
is an upward force
on the electrons
that move the wire
• Generator effect –
When a wire with no
initial current is
moved in a
magnetic field, the
electrons in the wire
experience a
deflecting force
perpendicular to
their motion
Transformers
Alternating current in the
primary coil causes the
north-south polarity of the
electromagnet to change.
Increasing or decreasing
voltage through
electromagnetic
induction
Transformers
Choose words to fill in the blanks:
current
electromagnet
motor
generator
electric
wire
As an ______ current or moving charge passes
through a wire it produces a magnetic field. This
magnetic field around a ____ forms concentric
circles. A current-carrying coil of wire with many
loops forms an ____________ . Magnets
moved near—or even inside coils of wire induce
(cause) a ______ in the coil. Electromagnets can
be used as a ______ or _________ or simply
as a magnet that can be turned on and off.
Choose words to fill in the blanks:
mechanical
motor
turn
wire
An electric ______ is made when a permanent
magnet is used to produce a magnetic field in a
region where a loop of wire is mounted so that it
can ____ about an axis. As current passes
through the ____ , the wire spins as it is repelled
and attracted to the magnet. The motor converts
electrical energy into ___________ energy.
Choose words to fill in the blanks:
converts
electrical
generator
voltage
An electric _________ is a device that
rotates a coil of wire in a stationary magnetic
field inducing a _______ in the coil. The
generator ________ mechanical energy into
_________ energy.
Energy
Transformations
Energy Changes!!!!!!!
Energy
Energy is required to do
work.
Fuels are burnt to release
energy
The Sun is the ultimate
source of most of our energy
on Earth.
The Law of Conservation of Energy
• The total amount of energy on earth stays
the same; it can be neither created nor
destroyed.
– It can only be converted from one form to
another.
– If energy seems to disappear, then scientists
look for it – leading to many important
discoveries.
Law of Conservation of Energy
• In 1905, Albert Einstein said that mass
and energy can be converted into each
other.
• He showed that if matter is destroyed,
energy is created, and if energy is
destroyed mass is created. E = mc2
Conservation of energy
Energy cannot be created or destroyed. It
can only be transformed from one form
to another form.
Conservation of energy also means that the
total energy in the universe stays constant.
“Law of Conservation of Energy”
Energy can not be created or
destroyed, it can only change its
form.
To Conserve means:
1. to keep
2. to preserve
3. to maintain
If energy seems to get lost during a process, then we should look for it !!
Pendulum oscillation
GRAVITATIOINAL POTENTIAL ENERGY
MAXIMUM
MINIMUM
KINETIC ENERGY
MAXIMUM
ZERO
The total energy, gravitational
potential plus kinetic, remains
the same if there are no
significant resistive forces
Choose words to fill in the blanks:
created
energy
destroyed
total
According to the law of conservation of
energy, during transformations the _______
amount of __________ stays the same.
Energy can be not be ___________ or
____________ ; it can only change its form.
Energy Conversion
• Energy can be changed from one form to
another. Changes in the form of energy
are called energy conversions.
• Whenever energy is converted, some
heat will be released or lost in the
process
Energy conversions
• All forms of energy can be converted into
other forms.
– The sun’s energy through solar cells can be
converted directly into electricity.
– Green plants convert the sun’s energy
(electromagnetic) into starches and sugars
(chemical energy).
Other energy conversions
– In an electric motor, electrical energy is
converted to mechanical energy.
– In a battery, chemical energy is converted into
electrical energy.
– The mechanical energy of a waterfall is
converted to electrical energy in a generator.
Energy Conversions
• In an automobile
engine, fuel is burned
to convert chemical
energy into heat
energy. The heat
energy is then
changed into
mechanical energy.
Choose words to fill in the blanks:
conversions
form
energy
heat
Energy can be changed from one _______to
another. Changes in the form of _______
are called energy __________________ .
Whenever energy is converted, some _____
will be released or lost in the process.
Forms of energy
Energy can exist in many forms.
1. THERMAL
or HEAT ENERGY
This is the energy of an
object due to its
temperature.
2. LIGHT ENERGY
This is energy in the form
of visible electromagnetic
radiation.
3. ELECTRICAL ENERGY
This is the energy
transferred by an electric
current.
4. SOUND ENERGY
This is energy in the form
of a sound wave.
5. KINETIC/MECHANICAL
ENERGY
This is the energy
possessed by a moving
object.
Kinetic energy increases as
the object’s speed is
increased.
Also often called
‘Movement energy’
6. CHEMICAL ENERGY
This is energy that is released
when chemical reactions take
place.
Sources of chemical energy
include:
fuel, food and batteries.
7. NUCLEAR ENERGY
This is energy that is released
when nuclear reactions take
place.
This is the source of the
Sun’s energy.
8. POTENTIAL ENERGY
This is the energy possessed by an
object due to its position.
Gravitational Potential Energy
The gravitational potential energy of
an object increases if it is raised
upwards.
Elastic Potential Energy
This is the energy
stored in a stretched
or squashed object
- also known as strain
energy
Gravitational potential
energy being converted
into kinetic energy.
Chemical  Heat
Mechanical
Light
Chemical
Electrical
Light
Thermal
Electrical
Light
Chemical
Electrical
Mechanical
Electrical
Thermal
Mechanical
Electrical
Chemical
Sound
Mechanical
Light
Thermal
Sound
Electrical
Chemical
Thermal
Choose words to fill in the blanks:
chemical
electricity
mechanical
Solar
All forms of energy can be converted into other
forms, examples include:
o The sun’s energy through _______ cells can
be converted directly into ______________ .
o Green plants convert the sun’s energy
(electromagnetic) into starches and sugars
(_________________ energy).
o In an electric motor, electrical energy is
converted to ___________________ energy.
Choose words to fill in the blanks:
chemical
fuel
mechanical
waterfall
All forms of energy can be converted into other
forms, examples include:
o In a battery, __________ energy is converted
into electrical energy.
o The mechanical energy of a ___________ is
converted to electrical energy in a generator.
o In an automobile engine, _____ is burned to
convert chemical energy into heat energy.
The heat energy is then changed into
_________________ energy.
Sankey Diagrams
These are energy flow
diagrams that show how
well a device uses
energy.
INPUT
Device
The width of the flow
arrows is proportional to
the amount of energy
Wasted energy is shown
flowing downwards.
WASTED
OUTPUT
USEFUL
OUTPUT
Energy flow diagrams
GENERAL DIAGRAM
INPUT
ENERGY
DEVICE
CAUSING
ENERGY
CHANGE
WASTED
ENERGY
USEFUL
OUTPUT
ENERGY
Choose words to fill in the blanks:
diagrams
heat
energy
system
Energy flow ____________ show how
_________ is transformed as it moves
through a _____________ . Accounts for
the thermal energy (_______ ) given off
during that transformation.
An electric light bulb
electrical
energy
light
bulb
heat
energy
light
energy
Microphone
sound
energy
microphone
heat
energy
electrical
energy
Car engine
chemical
energy
car
engine
heat &
sound
energy
kinetic
energy
Photosynthesis
light
energy
plants
heat
energy
chemical
energy
Deep thoughts
1. Which of the forms of energy are most important to us in
our daily lives?
2. Electricity itself moves, but how does it cause other
things to suddenly move?
3. Name a few devices in which electricity causes
something to move in a circle.
4. Which of the forms of energy are most important to us in
our daily lives?
5. Which of the forms of energy are most important to us in
our daily lives?
6. Which of the forms of energy are most important to us in
our daily lives?
Energy Conversions
1.
2.
3.
4.
5.
6.
7.
8.
Fuel (chemical to thermal)
Water (thermal to mechanical)
Steam turbine (mechanical to mechanical)
Generator (mechanical to electrical)
Toaster (electrical to thermal)
Toast (thermal to chemical)
Condenser (thermal to chemical)
Emission control (chemical to thermal)
Complete the table below:
Device
Input energy
Main output
energy
Electric motor
electrical
Kinetic/mechanical
Car brakes
kinetic
heat
Falling object
gravitational
potential
Kinetic/mechanical
Candle
chemical
light
Generator
kinetic
electrical
Useful and wasted energy
Useful energy is energy transferred to where it is
required in the form that it is wanted.
Other forms of energy are referred to as ‘wasted’.
Wasted energy spreads out into the surroundings.
This is usually in the form of heat energy causing
the energy changing device and its surroundings to
become warmer. It is very difficult to ‘concentrate’
this energy again to make use of it.
Energy efficiency
Energy efficiency is a measure of how
usefully energy is converted by a device.
efficiency =
useful energy output
total energy input
As the useful energy output can never be
greater than the energy input the efficiency
can never be greater than 1.0
Energy efficient light bulbs
• These produce more useful
light energy for the same
amount of input electrical
energy.
• They waste less energy to
heat.
Improving efficiency
Decrease loss to heat by:
Reducing friction by using a lubricant (eg oil).
Reducing electrical resistance in electrical
circuits.
Reducing air resistance by using streamlined
shapes.
Reduce loss to sound by tightening the
loose parts of machinery.
Choose words to fill in the blanks:
Efficiency
Heat
Measure
Required
Wasted
Useful energy is transferred to where it is ____ in
the form that it is wanted. Other forms of energy
are referred to as ‘____ ’ or given off in the form of
heat. Strategies to reduce this ____ loss are
intended to improve the ____ of a device. Energy
efficiency is a ____ of how usefully energy is
converted by a device.
Choose words to fill in the blanks:
Efficiency
Heat
Measure
Required
Wasted
Useful energy is transferred to where it is required
in the form that it is wanted. Other forms of energy
are referred to as ‘wasted’ or given off in the form
of heat. Strategies to reduce this heat loss are
intended to improve the efficiency of a device.
Energy efficiency is a measure of how usefully
energy is converted by a device.
Choose words to fill in the blanks:
Conserve
Light bulbs
Reduce
Wasting
Energy efficient ____ ____ are designed to
produce more useful light energy for the same
amount of input electrical energy by ____ less
energy to heat. Use of energy efficient light bulbs
is one strategy to conserve or ____ our
consumption of energy. Within our homes there
are many strategies we can use to ____ energy.
Choose words to fill in the blanks:
Conserve
Light bulbs
Reduce
Wasting
Energy efficient light bulbs are designed to
produce more useful light energy for the same
amount of input electrical energy by wasting less
energy to heat. Use of energy efficient light bulbs
is one strategy to conserve or reduce our
consumption of energy. Within our homes there
are many strategies we can use to conserve
energy.
Question 1
Calculate the efficiency of an electric motor if it
produces 48J of useful kinetic energy when
supplied with 80J of electrical energy.
efficiency =
useful energy output
total energy input
efficiency = 48J ÷ 80J
efficiency of the motor = 0.6
Question 2
Calculate the useful light output of a light bulb of
efficiency 0.20 when it is of an electric motor if it
supplied with 400J of electrical energy.
efficiency =
useful energy output
total energy input
0.20 = useful energy ÷ 400J
useful energy = 0.20 x 400J
light output = 80J
Percentage efficiency
percentage efficiency = efficiency x 100
The greater the percentage of the energy
that is usefully transformed in a device, the
more efficient the device is.
The maximum percentage efficiency is 100%
Question 3
Calculate the percentage efficiency of a light bulb
if it produces 30J of light when supplied with 240J
of electrical energy.
efficiency =
useful energy output
total energy input
efficiency = 30J ÷ 240J
= 0.125
% efficiency = efficiency x 100
Percentage efficiency of light bulb = 12.5%