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ElectricityCan you fill in the symbols for the
circuit components using page 176 and
181
Today’s lesson
• 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
energy
electron
lamp
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cell
energy
electron
lamp
Can you copy this please?
Electrons
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Hi, I’m Eleanor the electron.
Coulomb of charge (electrons)
Think of it as a “bag of electrons” (containing 6000000000000000000 electrons!)
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Current
The number of Coulombs flowing past a point in the circuit every second.
I = Q/t
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A
I’m counting how many
coulombs of electrons go
past me every second
1 Amp = 1 coulomb per second
Current
The number of Coulombs flowing past a point in the circuit every second.
I = Q/t
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A
I’m counting how many
coulombs of electrons go
past me every second
1 Amp = 1 coulomb per secondCan you copy this please?
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Let’s build some circuits!
Do experiments 31.4 to 31.10 page 256-
257
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
☺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
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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I’m checking the difference in energy (per
coulomb) between the 2 red arrows
1 Volt = 1 Joule per coulomb
Voltage (p.d.)☺
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V
I’m checking the difference in energy (per
coulomb) before and after the lamp
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 circuitThe sum of the voltages across the lamps
equals the voltage across the cells
9 V
3 V 3 V 3 V
In a series circuitThe sum of the voltages across the lamps
equals the voltage across the cells
9 V
3 V 3 V 3 V
☺Can you copy this please?
Stand up!
In a parallel circuitIn a simple parallel circuit, voltage across each lamp equals the voltage across the cells
5 V
5 V
5 V
In a parallel circuitIn a simple parallel circuit, voltage across each lamp equals the voltage across the cells
5 V
5 V
5 V
☺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)
VA
Resistance = voltage/current R = V/I
Resistance
Measures how difficult it is for current to flow. Measured in Ohms (Ω)
Resistance = voltage/current R = V/I
☺Can you copy this please?
Ohm’s Law
• V = IR
V
RI X
Let’s measure a resistance!
Resistance of a lamp
AV
Resistance = voltage/current R = V/I
Vary the voltage and current using a variable resistor (rheostat). Plot a graph of resistance against current
Resistance of a lamp
V(V) I(A) R(Ω)
I(A)
R(Ω)
Homework!
Read pages 176 and 177Answer questions on page 177Due 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)
VA
Power = voltage x current P = VI
Power
The amount of energy used by a device per second, measured in Watts (Joules per second)
VA
Power = voltage x current P = VI
☺Can you copy this please?
Power of a lamp
AV
Power = voltage x current P = VI
Measure the power of the lamp at it’s operating voltage. What is the electrical energy being turned into?
Example
• A 200 W television is plugged into the 110V mains. What is the current in the television?
PIV 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
PIV X
Example
• A kettle uses 240V and 8A. What is its power?
PIV X
Example
• A kettle uses 240V and 8A. What is its power?
• P = VI = 240x8 = 1920W (=1.9kW)
PIV X
Remember
Power is the amount of energy used by a device per second, measured in Watts (Joules per second)
VA
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 = VItE = 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?
PIV 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 PIV X
Let’s try some questions!
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