What does d.c. stand for? What does a.c. stand for? What do you currently know about the electricity you get from a household plug? Voltage, frequency.

• What does d.c. stand for?

• What does a.c. stand for?

• What do you currently know about the electricity you get from a household plug? Voltage, frequency etc….

Starter

6.1 Alternating Current

• By the end of today:– You should know what is meant by

direct and alternating current.

– You should be able to recall the frequency of mains electricity.

– Most will be able to describe in detail how an oscilloscope can be used to measure the frequency.

5.1 Electric Circuits

• What is ac and dc?• http://www.bbc.co.uk/learningzone/clips/

direct-current-vs-alternating-current/4557.html

• Why is ac used?• http://www.bbc.co.uk/learningzone/clips/a-

short-history-of-direct-and-alternating-current/1870.html

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Direct

Alternating

What about this?

What is the peak-to-peak voltage?

How long (in seconds) is it for one complete wave?

Learning Tasks….1. Silently read pages 184-1852. Define, as fully as possible:

• Frequency• Live Wire• Neutral Wire• Oscilloscope• Y gain control• Time base control

3. What is the frequency and voltage of a mains circuit?

4. Summary questions 1 and 2 page 185

6.2 Cables and Plugs

In pairs devise five questions that could have the answer:

A 3 pin plug.

• By the end of today:– You will be able to name all the parts of

a plug and describe their function.

– You will be able to explain why they are made of certain materials.

– You will have had a go at wiring a plug

6.2 Cables and Plugs

6.2 Cables and Plugs

Blue wire NeutralBrown wire LiveGreen and Earthyellow stripes

Remember!

BLUE bottom Left

BROWN bottom Right

STRIPED goes Top

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Component Function Material Reason

Case

Pins

Fuse

Cable Grip

Outer Cable

Inner wire

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page 6.2 Cables and Plugs

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/electricity/mainselecact.shtml

By the end of this lesson (or finished for homework)

Produce a guide for the

incompetent on ‘how to

wire a plug’.

You choose how

to present your

work.

Why does a three pin plug have three pins?

Why is one pin longer than the others?

–Pages 188-189–What is a fuse used for? How does it work?

Draw a quick diagram with your explanation.

–What is a circuit breaker used for? How does this work?

–Why do we ‘earth’ large electrical devices?–SQ 1 and 2

6.4 Power and Potential

Difference

Power Power (watts) = Energy Transformed (joules)

Time (seconds)

This means the more powerful something is, the more energy is transferred every second.

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Power Power (watts) = Energy Transformed (joules)

Time (seconds)

For example:

If a bulb transforms 300 J of electrical energy into light in 3 second, the power is:

P = Energy Transformed ÷TimeP = 300 (J) ÷ 3 (s)P = 100 W

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Power in a circuit Power = Current x Potential Difference

(watts, W) = (ampere, A) x (volts, V)

P = I x V

For example:

If a bulb has a p.d. across it of 3.0V, and a current flowing through it of 2.0A then the power is:

P = I x VP = 2.0 (A) x 3.0 (V)P = 6.0 W

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6.5 Energy and Charge

Charge in a circuit Charge = Current x Time

(coulomb, C) = (ampere, A) x (seconds, s)

For example:

How much charge flows if a current of 2.0 A flows for 60 seconds?

Charge = Current x TimeCharge = 2.0 (A) x 60 (s)Charge = 120 C

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Energy in a circuitEnergy Transformed = Potential Difference × Charge

(joules, J) = (volts, V) x (coulomb, C)

For example:

How much energy is transformed when the p.d. is 30V and the charge is 2.0 C?

Energy = Potential Difference × Charge Energy = 30 (V) x 2.0 (C)Energy = 60 J

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