Electricity
Can you fill in the
symbols for the
circuit components
using page 176 and
181
Today’s lesson
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Electrical symbols
Charge
Series and Parallel circuits
Understand that current is the rate of flow
of charge
• Recall and use: Q = It
• Looking at current in different circuits
• Conventional current
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cell
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energy
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electron
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lamp
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cell
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energy
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electron
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Can you copy
this please?
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lamp
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Electrons
Hi, I’m Eleanor the
electron.
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Coulomb of charge (electrons)
Think of it as a “bag of electrons” (containing
6000000000000000000 electrons!)
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Current
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I’m counting
how many
coulombs of
electrons go
past me every
second
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The number of
Coulombs flowing
A
past a point in the
circuit every second.
I = Q/t
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1 Amp = 1 coulomb per second
Current
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Can you copy
this please?
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I’m counting
how many
coulombs of
electrons go
past me every
second
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The number of
Coulombs flowing
A
past a point in the
circuit every second.
I = Q/t
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1 Amp = 1 coulomb per second
Let’s build some
circuits!
Do experiments 31.4
to 31.10 page 256257
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In a series circuit
Current is the same at any point in the circuit
2.5 A
2.5 A
2.5 A
2.5 A
In a series circuit
Current is the same at any point in the circuit
2.5 A
2.5 A
2.5 A
2.5 A
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Can you copy
this please?
Today’s lesson
• Looking at current in different circuits
• Recall and use: Q = It
• Understand that voltage is the number of
joules per coulomb transferred
• Looking at voltage in different circuits
In a parallel circuit
The current splits (total current stays the
same)
2.5 A
2.5 A
1.25 A
1.25 A
In a parallel circuit
The current splits (total current stays the
same)
2.5 A
2.5 A
1.25 A
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1.25 A
Can you copy
this please?
Milliamps!
1 A = 1000 mA
1 mA = ?
Milliamps!
1 A = 1000 mA
1 mA = 0.001 A
Stand
up!
Voltage(emf)
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V
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I’m checking the
difference in
energy (per
coulomb) between
the 2 red arrows
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1 Volt = 1 Joule per coulomb
Voltage (p.d.)
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I’m checking the
difference in
energy (per
coulomb) before
and after the lamp
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V
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1 Volt = 1 Joule per coulomb
Voltage
Voltage is the amount of energy transferred
(changed) per coulomb of charge.
Let’s build
some
circuits!
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Stand
up!
In a series circuit
The sum of the voltages across the lamps
equals the voltage across the cells
9V
3V
3V
3V
In a series circuit
The sum of the voltages across the lamps
equals the voltage across the cells
9V
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3V
3V
3V
Can you copy
this please?
Stand
up!
In a parallel circuit
In a simple parallel circuit, voltage across
each lamp equals the voltage across the
cells
5V
5V
5V
In a parallel circuit
In a simple parallel circuit, voltage across
each lamp equals the voltage across the
cells
5V
5V
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5V
Can you copy
this please?
Today’s lesson
• Understand the term resistance
• Recall and use: V =IR
Stand
up!
Resistance
Measures how difficult it is for current to
flow. Measured in Ohms (Ω)
V
Resistance = voltage/current
A
R = V/I
Resistance
Measures how difficult it is for current to
flow. Measured in Ohms (Ω)
V
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A
Can you copy
this please?
Resistance = voltage/current
R = V/I
Ohm’s Law
• V = IR
V
I
X
R
Let’s
measure a
resistance!
Resistance of a lamp
Vary the voltage and current using a variable resistor
(rheostat). Plot a graph of resistance against current
V
Resistance = voltage/current
A
R = V/I
Resistance of a lamp
V(V) I(A)
R(Ω)
R(Ω)
I(A)
Homework!
Read pages 176 and 177
Answer questions on page 177
Due Wednesday 25th November
Resistance of a lamp
• As the current in a lamp increases, it gets
hotter, and its resistance increases. Why?
Resistance of a lamp
• As the current in a lamp increases, it gets
hotter, and its resistance increases.
Copy please.
Let’s try some
resistance
questions
Today’s lesson
• Understand the term power
• Recall and use: P =VI
• Recall and use E = VIt
Power
The amount of energy used by a device
per second, measured in Watts (Joules
per second)
A
V
Power = voltage x current
P = VI
Power
The amount of energy used by a device
per second, measured in Watts (Joules
per second)
A
V
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Can you copy
this please?
Power = voltage x current
P = VI
Power of a lamp
Measure the power of the lamp at it’s operating voltage.
What is the electrical energy being turned into?
A
V
Power = voltage x current
P = VI
Example
• A 200 W television is plugged into the
110V mains. What is the current in the
television?
P
V I
X
Example
• A 200 W television is plugged into the
110V mains. What is the current in the
television?
• I = P/V = 200/110 = 1.8A
P
V I
X
Example
• A kettle uses 240V and 8A. What is its
power?
P
V I
X
Example
• A kettle uses 240V and 8A. What is its
power?
• P = VI = 240x8 = 1920W (=1.9kW)
P
V I
X
Remember
Power is the amount of energy used by a
device per second, measured in Watts
(Joules per second)
A
V
Power = voltage x current
P = VI
Total energy
So the total energy transformed by a lamp
is the power (J/s) times the time the lamp
is on for in seconds,
E = VIt
E = energy transformed (J)
V = Voltage (also called p.d.)
I = current (A)
t = time (s)
Example
• A kettle uses 240V and 8A. What is its
power?
• P = VI = 240x8 = 1920W (=1.9kW)
• How much energy does the kettle use in 5
minutes?
P
V I
X
Example
• A kettle uses 240V and 8A. What is its
power?
• P = VI = 240x8 = 1920W (=1.9kW)
• How much energy does the kettle use in 5
minutes?
• E = VIt = 240x8x300 = 576000 J
P
V I
X
Simple!
Let’s try some questions!