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

Simple!

Let’s try some questions!