Thomas Edison 1847-1931

3V

1.5V1.5V

What happens if the bulbs have different resistances?

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3V

2

In a SERIES circuit, the total RESISTANCE is the sum of all of the resistances added together, so 2 + 3 = 5

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3

So, what is the current through the 2 bulb?

Remember, V = IR

6 = I x 2

6/2 = 3A

N

Circuit 1* Circuit 2

Two different circuits – what is different?

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Circuit 3

N

Circuit 1* Circuit 2 Circuit 4

Build the following circuits and record the brightness of the bulbs

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N

Circuit 1* Circuit 3Circuit 2 Circuit 4

N

N

N

N

N

N

N

N

N

Build the following circuits and record the brightness of the bulbs

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Conclusion: In a parallel circuit, the potential difference across all components is the same.

A3

A2

A1A1 , A2 and A3 are ammeters.

Remember: In a parallel circuit, the total current in the branches is the same as the current in the rest of the circuit.Or . . A1 = A2 + A3

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In a parallel circuit, the current splits between the branches.

Example 1.Ammeter A2 reads 0.18 amps and ammeter A3 reads 0.24 amps. What does ammeter A1 read ?

A1 = 0.42 amps

A1 = 0.18 + 0.24

A1 = A2 + A3

A3

A2

A1

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Example 2.Ammeter A1 reads 0.36 amps and ammeter A3 reads 0.22 amps. What does ammeter A2 read ?

A1 = A2 + A3

A2 = 0.14 amps

A2 = 0.36 ▬ 0.22

0.36 = A2 + 0.22

A3

A2

A1

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Conclusion:

Current is the shared between the branches of a parallel circuit.

Potential Difference is equal across the components in a parallel circuit.

Resistance depends on the current flowing through the component (as PD is the same). The bigger the resistance, the smaller the current.

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What happens if we change the resistance of each bulb?

Calculate the current through each bulb. (V = IR)

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6V

1

2

3

I = V/R = 6/1 = 6A

I = V/R = 6/2 = 3A

I = V/R = 6/3 = 2A

Total I = 6 + 3 + 2 = 11A

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Answer Exam Style Questions

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Flow of current.

• In a torch the current flows around in one direction – we call this d.c. (direct current).

• Electricity in the home uses a.c. (alternating current) which changes direction repeatedly.

• The frequency of an a.c. supply is the number of cycles it passes through per second. In the UK is 50Hz (50 times per second).

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Potential Difference

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Plugs

• Need a live wire (its PD changes every second)

• Need a neutral wire (connected to an Earth at the local sub station).

• Some items also have an additional Earth (metallic items in particular).

• The case is made of an insulator.

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Plugs

Which pin is longer and why?

The Earth is longest – so the appliance is Earthed first.

What alloy is used to make the contacts inside the plug?

Brass (it is harder than copper)

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Wire a plug

Green & Yellow – Earth

Blue (or black) – Neutral

Brown (or red) - Live

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Fuses

Lengths of wire, which when get to hot melt and break the circuit.

A fuse provides NO protection against electrocution more than 20mA which can be lethal and so items must be EARTHED.

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Circuit breaker.It is an electromagnetic switch that open (cuts off) when the current is too high.

It can be reset once the fault has been corrected.

They are faster than fuses.

They can be reset quicker.

Are you now able to….

I still feel unsure. I need some more help to understand.

I feel ok. I need to do some more work to check my understanding.

I am happy and feel I understand and can explain the main points.