Transcript Slide 1

P2.3.2 Electrical Circuits
P2 Physics
Mr D Powell
Connection
• Connect your learning to the
content of the lesson
• Share the process by which the
learning will actually take place
• Explore the outcomes of the
learning, emphasising why this will
be beneficial for the learner
Demonstration
• Use formative feedback – Assessment for
Learning
• Vary the groupings within the classroom
for the purpose of learning – individual;
pair; group/team; friendship; teacher
selected; single sex; mixed sex
• Offer different ways for the students to
demonstrate their understanding
• Allow the students to “show off” their
learning
Activation
• Construct problem-solving
challenges for the students
• Use a multi-sensory approach – VAK
• Promote a language of learning to
enable the students to talk about
their progress or obstacles to it
• Learning as an active process, so the
students aren’t passive receptors
Consolidation
• Structure active reflection on the lesson
content and the process of learning
• Seek transfer between “subjects”
• Review the learning from this lesson and
preview the learning for the next
• Promote ways in which the students will
remember
• A “news broadcast” approach to learning
Mr Powell 2012
Index
P2.3.2 Electrical circuits (Part A)
a) Electric current is a flow of electric charge. The size of the electric current is
the rate of flow of electric charge. The size of the current is given by the
equation:
I = Q/t (or Q = It )
I is the current in amperes (amps), A
Q is the charge in coulombs, C
t is the time in seconds, s
b) The potential difference (voltage) between two points in an electric circuit is
the work done (energy transferred) per coulomb of charge that passes
between the points.
V = W/Q
V is the potential difference in volts, V
W is the work done in joules, J
Q is the charge in coulombs, C
Mr Powell 2012
Index
a) Current flow...
Mr Powell 2012
Index
a) Coulombs

Electrons are charged particles and each of them have a charge of 1.9 x 10-19 C.

It is a simple property which cannot be removed or changed. It is a useful to us
as charges make particles move i.e. opposites attract.

If we add a load of them together and think of them as a single “sphere of
charge” or ball we get a whole coulomb of charge and can think about defining
the ampere or amp 1A = 1C/s
C
ee- e-- e-- ee- - e- e- e-e e e- e e
e- e- ee-
1.9 x 10-19 C x 6.25 x 1018 electrons = 1C
Mr Powell 2012
Index
a) What is an electric current....
When a torch lamp is on, millions of electrons pass through it every
second. The electric current through the lamp is due to electrons
passing through it. Each electron carries a tiny negative charge. The rate
of flow of electrical charge is called the current. The filament of the
torch lamp is a fine metal wire. Metals conduct electricity because they
contain conduction (or sea of delocalised) electrons. These electrons
move about freely inside the metal. They are not confined to a single
atom. When the torch is switched on, the battery pushes electrons
through the filament. Insulators can’t conduct electricity because all the
electrons are held in atoms.
TASK: explain what an electric C
current is. Why do metals
conduct and plastics do not?
draw an atomic structure diagram
to help you compare and
B
model the idea..
A
Mr Powell 2012
Index
a) Q = It
 When electrons move through a wire we call it an electrical current. The
electrons move as there is a potential difference.
 The larger the p.d. the higher the current flow or Coulombs per second.
 1A = 1Cs-1
 A simple graph of this process would be where a steady current has
flowed for 20s seconds;
 The number of Coulombs of charge that have flowed is 100C
Mr Powell 2012
Index
Potential Difference Theory
Potential Difference: is defined as the work done (or energy transfer) per unit charge
V (Volt)
=
W
Q
(work done, J)
(charge, C)
+
B
If 1J of work is done in moving 1 C
of positive charge from A to B then the
Pd is 1V
A
+
1V = 1 J / C
Mr Powell 2012
Index
b) V = W/Q - Example

This process whereby ions exchange electrons through a molten
liquid or dissolved solid is also a way in which a “current” flows.
Also a PD between ground and cloud causing a spark to move.

As charge carriers are moving. Hence we can say that energy
converted is;
E = QV
E = 5C x 3000V = 15000J
or
E = VIt
E = 3V x 2A x 3s
E = 18J
Mr Powell 2012
Index
a& b) Circuits Theory Summary.....
Voltage is really a measure of the difference of energy before and
after a component. It is measured in volts, symbol V. 1 Volt is equal to
1 joule of energy for each coulomb of charge which passes through
the circuit. A voltmeter is connected in parallel with a component.
1V = 1J/C
Current is the flow of groups of electrons. One group has a coulomb
of charge (since each electron has a little bit of charge). We call a flow
of one coulomb per second an ampere, amp, symbol A. An ammeter
is connected in series.
1A = 1C/s
Mr Powell 2012
Index
P2.3.2 Electrical circuits (Part A)
a) Electric current is a flow of electric
charge. The size of the electric
current is the rate of flow of
electric charge. The size of the
current is given by the
equation:
I = Q/t (or Q = It )
I is the current in amperes
(amps), A
Q is the charge in coulombs, C
t is the time in seconds, s
P2.3.2 Electrical circuits (Part A)
a) Electric current is a flow of electric
charge. The size of the electric
current is the rate of flow of
electric charge. The size of the
current is given by the
equation:
I = Q/t (or Q = It )
I is the current in amperes
(amps), A
Q is the charge in coulombs, C
t is the time in seconds, s
P2.3.2 Electrical circuits (Part A)
a) Electric current is a flow of electric
charge. The size of the electric
current is the rate of flow of
electric charge. The size of the
current is given by the
equation:
I = Q/t (or Q = It )
I is the current in amperes
(amps), A
Q is the charge in coulombs, C
t is the time in seconds, s
b) The potential difference (voltage)
between two points in an
electric circuit is the work done
(energy transferred) per
coulomb of charge that passes
between the points.
b) The potential difference (voltage)
between two points in an
electric circuit is the work done
(energy transferred) per
coulomb of charge that passes
between the points.
b) The potential difference (voltage)
between two points in an
electric circuit is the work done
(energy transferred) per
coulomb of charge that passes
between the points.
V = W/Q
V = W/Q
V = W/Q
V is the potential difference in
volts, V
W is the work done in joules, J
Q is the charge in coulombs, C
V is the potential difference in
volts, V
W is the work done in joules, J
Q is the charge in coulombs, C
V is the potential difference in
volts, V
W is the work done in joules, J
Q is the charge in coulombs, C
P2.3.2 Electrical circuits (Part B)
f) The resistance of a component can be
found by measuring the current through,
and potential difference across, the
component.
g) The current through a resistor (at a
constant temperature) is directly
proportional to the potential difference
across the resistor.
h) Calculate current, potential difference
or resistance using the equation:
V = IR
V is the potential difference in volts, V
I is the current in amperes (amps), A
R is the resistance in ohms, 
Mr Powell 2012
Index
f/g/h ) Investigating Components
Build the circuit as shown on the
slide.
It may be that the switch and
variable resistor is inside the power
pack.
Investigate how the resistance of a;
1.
2.
Resistor
Filament lamp
Changes as you change the potential
difference of the power pack from 6V -> 0 -> 6V in steps of 1V
Draw a graph to show your results
(line graph with 0,0 in the centre of
the page.
Voltage (V)
Current (A)
Resistance
(Ω)
R
-6
-4
...
...
+6
Mr Powell 2012
Index
V
I
f/g/h ) Graphing Resistance
Now you have your raw data
work out the resistance of the
device by the following formula;
R = resistance (Ohms - )
I = Current (Amperes - A)
V = potential difference (Volts - V)
Split a sheet of graph paper into
4. Then construct and comment
on these graphs......
X- Axis
Y-Axis
Voltage
Current
Current
Voltage
Length
Resistance
V
R
I
Worked example
The current through a wire is 2.0 A
when the potential difference across it
is 12V.
Solution
Mr Powell 2012
Index
f/g/h ) Analysis
Look at the data on the this graph
and answer the following
questions...
1) When the p.d. Is 1V then 2V
what are the corresponding
currents?
2) What can you say about the
relationship between current
and voltage?
3) What does the gradient of
the graph represent?
4) Can you work out the
resistance of this wire?
Mr Powell 2012
Index
f/g/h ) Summary Questions
Mr Powell 2012
Index
P2.3.2 Electrical circuits (Part B)
P2.3.2 Electrical circuits (Part B)
P2.3.2 Electrical circuits (Part B)
f) The resistance of a component
can be found by measuring the
current through, and potential
difference across, the component.
f) The resistance of a component
can be found by measuring the
current through, and potential
difference across, the component.
f) The resistance of a component
can be found by measuring the
current through, and potential
difference across, the component.
g) The current through a resistor (at
a constant temperature) is directly
proportional to the potential
difference across the resistor.
g) The current through a resistor (at
a constant temperature) is directly
proportional to the potential
difference across the resistor.
g) The current through a resistor (at
a constant temperature) is directly
proportional to the potential
difference across the resistor.
h) Calculate current, potential
difference or resistance using the
equation:
V = IR
h) Calculate current, potential
difference or resistance using the
equation:
V = IR
h) Calculate current, potential
difference or resistance using the
equation:
V = IR
V is the potential difference in volts,
V
I is the current in amperes (amps),
A
R is the resistance in ohms, 
V is the potential difference in volts,
V
I is the current in amperes (amps),
A
R is the resistance in ohms, 
V is the potential difference in volts,
V
I is the current in amperes (amps),
A
R is the resistance in ohms, 
P2.3.2 Electrical circuits (Part C)
c) Circuit diagrams using standard symbols (see next slide):
d) VI graphs are used to show how the current through a
component varies with the potential difference across it.
e) The VI graphs for a resistor at constant temperature.
m) The resistance of a filament bulb increases as the temperature of
the filament increases. (explain resistance change in terms of ions
and electrons.)
o) & n) The current through a diode flows in one direction only. The
diode has a very high resistance in the reverse direction. LED as
example turn on in forwards direction only.
p) The resistance of a light-dependent resistor (LDR) decreases as
light intensity increases.
q) The resistance of a thermistor decreases as the temperature
increases.
Mr Powell 2012
Index
Circuit Symbols
Candidates will be
required to interpret and
draw circuit
diagrams.
Knowledge and
understanding of the use
of thermistors in circuits
e.g. thermostats is
required.
Knowledge and
understanding of the
applications of lightdependent resistors
(LDRs) is required, eg
switching lights on when
it gets dark
Mr Powell 2012
Index
Simple Circuits
Electrical circuits of many different types
are found around us in nearly every
device we have in the home, at work and
in school.
We can draw a picture like this for each
one but a real circuit diagram is a very
helpful way of showing how the
components in a circuit are connected
together.
Each component has its own symbol
which makes them simple to understand
when they get complex.
1) Can you draw a circuit diagram
with the proper symbols (use a
ruler)
2) Can you remember any special
rules about the potential
difference or current from you
previous studies?
Mr Powell 2012
Index
What is the symbol?
1
2
3
4
5
Mr Powell 2012
Index
Symbols6 II
7
8
9
10
cell
Low resistance, connect in series
Indicator / light source
No more semi circles!
resistor
thermistor
Electric motor
High resistance, connect in parallel
Resistance falls as temp rises
ammeter
Resistance falls as light level rises
Light emitting diode
Light dependent resistor
heater
Emits light when forward biased
of a specific value
voltmeter
Conducts when forward biased
diode
Variable resistor
Many cells = a battery
e) Resistor
As the voltage increases the current also
increases at the same rate. The resistance is
constant. (Directly Proportional)
This is what is called “ohms law”
True only for a resistor at a constant
temperature
Mr Powell 2012
Index
Mr Powell 2012
Index
m) Filament Lamps
The resistance of a filament lamp increases as the
temperature of the filament increases. The atoms
get very hot and vibrate so slow the electrons
down.
The resistance & gradient changes as the
temperature of the wire changes
Mr Powell 2012
Index
Mr Powell 2012
Index
O & n) Diode
The current through a diode flows in one
direction only. The diode has a very high
resistance in the reverse direction.
Often used in mobile phone transformers to
change A.C. to D.C. currents.
Mr Powell 2012
Index
p) LDR
The resistance of a light-dependent resistor
(LDR) decreases as light intensity increases. This
is weird as it is the opposite of what you might
expect of a normal resistor. The light frees the
electrons.
You might see two types of graph one normal
and one in logarithmic form to make a trend
easier to see!
Mr Powell 2012
Index
q) Thermistor
The resistance of a thermistor decreases as
the temperature increases. So the extra
heat allows electrons to flow.
This is weird and opposite to normal
resistors!
Mr Powell 2012
Index
Simple Circuits Practical
Connect a variable resistor in series with the
torch lamp and a battery, as shown in the
diagram. Adjusting the slider of the variable
resistor alters the amount of current flowing
through the bulb and therefore affects its
brightness. The torch lamp goes dim when
the slider is moved one way. (You can add an
ammeter to check the flow.)
We can also control currents to only allow
them to flow one way. The diode prevents
flow in one direction to protect the radio if
the cell it put in the wrong way.
1) What happens if the slider is
moved back again?
2) What happens if you have
two bulbs in your circuit?
2) What happens if you include a
diode in the circuit, try it both
ways around?
4) Why might you put a diode in
a radio circuit?
Mr Powell 2012
Index
Summary Questions
1.
2.
3.
4.
Cell
Switch
Bulb
Fuse

Diode should have the arrow in
the direction of pos to neg

Variable resistor or fixed resistor
Mr Powell 2012
Index
P2.3.2 Electrical circuits (Part C)
P2.3.2 Electrical circuits (Part C)
P2.3.2 Electrical circuits (Part C)
c) Circuit diagrams using standard
symbols (see next slide):
c) Circuit diagrams using standard
symbols (see next slide):
c) Circuit diagrams using standard
symbols (see next slide):
d) VI graphs are used to show how
the current through a component
varies with the potential difference
across it.
d) VI graphs are used to show how
the current through a component
varies with the potential difference
across it.
d) VI graphs are used to show how
the current through a component
varies with the potential difference
across it.
e) The VI graphs for a resistor at
constant temperature.
e) The VI graphs for a resistor at
constant temperature.
e) The VI graphs for a resistor at
constant temperature.
m) The resistance of a filament bulb
increases as the temperature of the
filament increases. (explain
resistance change in terms of ions
and electrons.)
m) The resistance of a filament bulb
increases as the temperature of the
filament increases. (explain
resistance change in terms of ions
and electrons.)
m) The resistance of a filament bulb
increases as the temperature of the
filament increases. (explain
resistance change in terms of ions
and electrons.)
o) & n) The current through a diode
flows in one direction only. The
diode has a very high resistance in
the reverse direction. LED as
example turn on in forwards
direction only.
o) & n) The current through a diode
flows in one direction only. The
diode has a very high resistance in
the reverse direction. LED as
example turn on in forwards
direction only.
o) & n) The current through a diode
flows in one direction only. The
diode has a very high resistance in
the reverse direction. LED as
example turn on in forwards
direction only.
p) The resistance of a lightdependent resistor (LDR) decreases
as light intensity increases.
p) The resistance of a lightdependent resistor (LDR) decreases
as light intensity increases.
p) The resistance of a lightdependent resistor (LDR) decreases
as light intensity increases.
q) The resistance of a thermistor
decreases as the temperature
increases.
q) The resistance of a thermistor
decreases as the temperature
increases.
q) The resistance of a thermistor
decreases as the temperature
increases.
Starter: What am I...
I like to live in a low pressure argon atmosphere
I am made of metal
I can conduct electricity easily
When I am skinny I like to resist current
I got hot in the right conditions
I glow a lot in the right conditions
I am a very curly
Mr Powell 2012
Index
P2.3.2 Electrical circuits (Part D)
i) The current through a component depends on its resistance. The greater the
resistance the smaller the current for a given p.d. across the component.
j) The p.d. provided by cells connected in series adds up.
k) For components connected in series:
 the resistance adds up.
 there is the same current through each component
 the total p.d. is shared
I) For components connected in parallel:
 the p.d. across each component is the same
 The current splits at branches
Mr Powell 2012
Index
1 Series Questions
1) A cell, a resistor, a lamp and an ammeter are connected in
series;
a)
The current through the battery is …………………… the current through
the ammeter.
b) The potential difference across the battery is …………………. the
potential difference across the resistor.
c) The current through the lamp is ……………… the current through the
resistor.
d) The potential difference across the lamp is ……………… the potential
difference across the battery.
greater than
less than
the same as
Mr Powell 2012
Index
Series PD
3.0 V
3 V
4
3 V
4
V
V
A
V
In a series circuit
the current is the
same
everywhere
V
V
3 V
4
3 V
4
0.1 A
In a series circuit
the PD is shared
among the
components
Mr Powell 2012
Index
2 Potential Difference Series.....
2) the cell has a potential difference
of 3.0 V and the resistor has a
resistance of 8.0 . The ammeter
reading is 0.2 A.
a)
Calculate the potential
difference across the resistor?
b) Calculate the potential
difference across the lamp?
Answers
a)
V = IR so 0.2A x 8  = 1.6V
b) 3V – 1.6V = 1.4V
Energy / PD Rule
 In a series circuit the
energy is shared
between components
 V = IR
Mr Powell 2012
Index
3 Potential Difference Series.....
3) A battery, an ammeter, a 10 
resistor and a 15  resistor are
connected in series. The ammeter
reading is 0.36 A. Calculate the
potential difference across:
a)
the 10  resistor.
b) the 15  resistor.
Answers
c)
a)
the battery.
d) What would be the resistance of
a single resistor that would have
the same current if it was
connected on its own to the
same battery?
V = IR so 0.36A x 10  = 3.6V
b) V = IR so 0.36A x 15  = 5.4V
c)
Vs = 3.6V + 5.4V = 9V
d) V=IR or V/I = R 9V/0.36A = 25 
Mr Powell 2012
Index
4 Potential Difference Series.....
4) A 6.0 V battery, a 10  resistor and
a 20  resistor are connected in
series with each other.
a)
Draw out a circuit diagram
Answers
a)
All connected in series
b) Calculate the total resistance of
the two resistors in series.
b) RT = R1 + R2 = 10 +20  = 30 
c)
c)
Calculate the current in the
circuit.
V=IR or V/R = I I = 6V / 30  = 0.2A
d) V = IR , 0.2A x 20  = 4V
d) Calculate the potential
difference across the 20 
resistor.
Mr Powell 2012
Index
5 Parallel Questions.....
2) the cell has a potential difference of 2.0 V and
the resistor has a resistance of 5.0 . The
ammeter reading is 0.9 A.
a)
Show that the current through the resistor
is 0.4 A.
b)
The ammeter reading is 0.9 A. Calculate the
current through the lamp.
Resistors in Parallel Rules
c)
Calculate the resistance of the lamp in this
circuit.
Answers
a)
V = IR so V/R = I so 2V /5  = 0.4A
 Each branch has P.D. of cell
 Current splits at branches
according to resistance
b) 0.9A – 0.4A = 0.5A
c)
V = IR so V/I = R 2V/0.5A = 4 
Mr Powell 2012
Index
6 Parallel Questions.....
3) A 12 V battery is connected to a 10 
resistor in parallel with a 15  resistor, as
shown. Calculate the current through:
a)
the 10  resistor.
b) the 15  resistor.
c)
Answers
a)
the battery.
d) What would be the resistance of a
single resistor that would have the
same current if it was connected on
its own to the same battery?
1
1
1
 
RT R1 R2
V = IR so V/R = I so 12V /10  =
1.2A
b) V = IR so V/R = I so 12V /15  =
0.8A
c)
0.8A + 1.2A = 2 A
d) V = IR , V/I = R 12V / 2A = 6 
Or 1/R T=1/10+1/15 = 0.167 RT = 6 
Mr Powell 2012
Index
P2.3.2 Electrical circuits (Part D)
P2.3.2 Electrical circuits (Part D)
i) The current through a component depends on its
resistance. The greater the resistance the smaller the
current for a given p.d. across the component.
i) The current through a component depends on its
resistance. The greater the resistance the smaller the
current for a given p.d. across the component.
j) The p.d. provided by cells connected in series adds up.
j) The p.d. provided by cells connected in series adds up.
k) For components connected in series:

the resistance adds up.

there is the same current through each
component

the total p.d. is shared
k) For components connected in series:

the resistance adds up.

there is the same current through each
component

the total p.d. is shared
I) For components connected in parallel:

the p.d. across each component is the
same

The current splits at branches
I) For components connected in parallel:

the p.d. across each component is the
same

The current splits at branches
P2.3.2 Electrical circuits (Part D)
P2.3.2 Electrical circuits (Part D)
i) The current through a component depends on its
resistance. The greater the resistance the smaller the
current for a given p.d. across the component.
i) The current through a component depends on its
resistance. The greater the resistance the smaller the
current for a given p.d. across the component.
j) The p.d. provided by cells connected in series adds up.
j) The p.d. provided by cells connected in series adds up.
k) For components connected in series:

the resistance adds up.

there is the same current through each
component

the total p.d. is shared
k) For components connected in series:

the resistance adds up.

there is the same current through each
component

the total p.d. is shared
I) For components connected in parallel:

the p.d. across each component is the
same

The current splits at branches
I) For components connected in parallel:

the p.d. across each component is the
same

The current splits at branches
Pracs / Demos
Suggested ideas for practical work to develop skills and understanding include the
following:
■ using filament bulbs and resistors to investigate potential difference/current
characteristics
■ investigating potential difference/current characteristics for LDRs and thermistors
■ setting up series and parallel circuits to investigate current and potential difference
■ plan and carry out an investigation to find the relationship between the resistance
of thermistors and their temperature
■ investigating the change of resistance of LDRs with light intensity.
Mr Powell 2012
Index