P2.4.1 Household Electricity

P2 Physics

KS4 ADDITIONAL SCIENCEMr D Powell

Mr Powell 2012Index

Connection

• Connect your learning to the content of the lesson

• Share the process by which the learning will actually take place

• Explore the outcomes of the learning, emphasising why this will be beneficial for the learner

Demonstration

• Use formative feedback – Assessment for Learning

• Vary the groupings within the classroom for the purpose of learning – individual; pair; group/team; friendship; teacher selected; single sex; mixed sex

• Offer different ways for the students to demonstrate their understanding

• Allow the students to “show off” their learning

Activation

• Construct problem-solving challenges for the students

• Use a multi-sensory approach – VAK• Promote a language of learning to

enable the students to talk about their progress or obstacles to it

• Learning as an active process, so the students aren’t passive receptors

Consolidation

• Structure active reflection on the lesson content and the process of learning

• Seek transfer between “subjects”• Review the learning from this lesson and

preview the learning for the next• Promote ways in which the students will

remember• A “news broadcast” approach to learning

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P2.4.1 Household Electricity (Part A)

a) Cells and batteries supply current that always passes in the same direction. This is called direct current (d.c.).

b) An alternating current (a.c.) is one that is constantly changing direction.

c) Mains electricity is an a.c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz) and is about 230 V.

d) Most electrical appliances are connected to the mains using cable and a three-pin plug.

e) The structure of electrical cable.

f) The structure and wiring of a three-pin plug.

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P5.1 – Alternating Current p164

a) Cells and batteries supply current that always passes in the same direction. This is called direct current (d.c.).

b) An alternating current (a.c.) is one that is constantly changing direction.

c) Mains electricity is an a.c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz) and is about 230 V.

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Signal Generator & Oscilloscope - Video

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Signal Generator & Oscilloscope

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D.C. versus A.C.

Direct Current

If the _______flows in only one direction it is called ______ _______, or dc. Batteries and cells supply ___ _____electricity. The diagram shows the trace from an oscilloscope showing the signal from a DC supply. The voltage is ___V.

Alternating Current

If the _______ constantly changes direction it is called ___________ current, or ac. Mains electricity is an ____ ______ supply. The UK mains supply is about 230V. It has a frequency of ___ Hz (50 Hertz), which means that it changes direction __ times a second. The diagram shows an oscilloscope screen displaying the signal from an ac supply. The peak voltage is ___V.

Scale = 1V/cm

Scale = 300V/cm

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1 AC Problems

1) An a.c. source is connected to an oscilloscope. The waveform of the alternating potential difference from the source is displayed on the oscilloscope screen as below.

a) The Y-gain setting of the oscilloscope is 0.5 V/cm. Determine the amplitude of the alternating potential difference.

The time-base setting of the oscilloscope is 0.02 seconds per cm.

b. Show that the time for one cycle of the waveform is 0.06 s.

c. Calculate the frequency of the alternating potential difference.

a) 0.5V/cm x 2cm = 1V

b) 1 cycle is 3 cm so ;3 x 0.02 s/cm = 0.06s

c) 1/T = f so 1/0.06s = 16.67s-1 or 17 Hz

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2 AC Problems...

2) An a.c. source is connected to an oscilloscope. The waveform of the alternating potential difference from the source is displayed on the oscilloscope screen as below.

a) The Y-gain setting of the oscilloscope is 2.0 V/cm. Determine the amplitude of the alternating potential difference.

The time-base setting of the oscilloscope is 0.010 seconds per cm.

b) Determine the frequency of the alternating potential difference.

c) The a.c. supply is disconnected and a horizontal flat trace across the middle of the screen is seen. Sketch the trace that you would expect to see if the a.c. supply was replaced by a battery of p.d. 3.0 V.

a) 2V/cm x 2.5cm = 5V

b) 1 cycle is 2 cm so ; 2 x 0.01 s/cm = 0.02s 1/T = f so 1/0.02s = 50s-1 or

50 Hz

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P5.2 – Cables and Plugs – p166

d) Most electrical appliances are connected to the mains using cable and a three-pin plug.

e) The structure of electrical cable.

f) The structure and wiring of a three-pin plug.

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Sockets – Ring Mains

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3 Pin Plug

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Plug Features

Copper is used for the wires because it is a good electrical conductor and soft or malleable. This means it bends when you flex the wire.

Plastic is a good electrical insulator and therefore prevents anyone touching the cable from receiving an electric shock.

Brass (copper/ zinc) is used for the pins as it is a hard and durable alloy metal.

Two-core cables are used for appliances which have plastic cases(e.g. hairdryers, radios).

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Plug Features II

The brown wire is connected to the live pin.

The blue wire is connected to the neutral pin.

The green-yellow wire (of a three-core cable) is connected to the earth pin.

The plug contains a fuse between the live pin and the live wire. The fuse melts and cuts the live wire off if too much current passes through it.

A two-core cable does not have an earth wire.

P2.4.1 Household Elect (Part A)

a) Cells and batteries supply current that always passes in the same direction. This is called direct current (d.c.).

b) An alternating current (a.c.) is one that is constantly changing direction.

c) Mains electricity is an a.c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz) and is about 230 V.

d) Most electrical appliances are connected to the mains using cable and a three-pin plug.

e) The structure of electrical cable.

f) The structure and wiring of a three-pin plug.

P2.4.1 Household Elect (Part A)

a) Cells and batteries supply current that always passes in the same direction. This is called direct current (d.c.).

b) An alternating current (a.c.) is one that is constantly changing direction.

c) Mains electricity is an a.c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz) and is about 230 V.

d) Most electrical appliances are connected to the mains using cable and a three-pin plug.

e) The structure of electrical cable.

f) The structure and wiring of a three-pin plug.

P2.4.1 Household Elect (Part A)

a) Cells and batteries supply current that always passes in the same direction. This is called direct current (d.c.).

b) An alternating current (a.c.) is one that is constantly changing direction.

c) Mains electricity is an a.c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz) and is about 230 V.

d) Most electrical appliances are connected to the mains using cable and a three-pin plug.

e) The structure of electrical cable.

f) The structure and wiring of a three-pin plug.

Mr Powell 2012Index

P2.4.1 Household Electricity (Part B) – 5.3 Fuses p168

g) If an electrical fault causes too great a current, the circuit is disconnected by a fuse or a circuit breaker in the live wire.

h) When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit. Some circuits are protected by Residual Current Circuit Breakers (RCCBs).

J) Appliances with metal cases are usually earthed.

k) The earth wire and fuse together protect the wiring of the circuit.

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A.C. In Plugs

The ………………………… of the live terminal varies between a large ……………….. value and a large ………………… value.

However, the …………………….. terminal is at a potential difference close to …………., which is zero.

The diagram shows an oscilloscope screen displaying the signals from the mains supply.

The ……….. trace is the ……….. terminal and the blue trace the neutral terminal.

The mean voltage of the mains supply is about …………, the peak voltage is higher. (325V) We use ………… in normal calculations.

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A.C. In Plugs

The potential difference of the live terminal varies between a large positive value and a large negative value.

However, the neutral terminal is at a potential difference close to earth, which is zero.

The diagram shows an oscilloscope screen displaying the signals from the mains supply.

The red trace is the live terminal and the blue trace the neutral terminal.

Note: although the mean voltage of the mains supply is about 230V, the peak voltage is higher. We use 230V in normal calculations.

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Summary Questions

neutral

liveparallel

Earth

series

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How is it all connected?

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Heater Circuit

3 Pin Plug / Mains

Inside 3 Pin Plug

Appliance

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Circuit Breakers

A circuit breaker is an electromagnetic switch that opens (i.e. ‘trips’) and cuts the current off if the current is greater than a certain value.

It can then be reset once the fault that made it trip has been put right.

Circuit breakers are sometimes fitted in ‘fuse boxes’ in place of fuses.

They work faster than fuses and can be reset quicker.

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Facts Fuses

Fuses are thin pieces of wire which resist a large current

They melt when too much current flows

Circuit is broken

Have to be replaced

Facts Circuit Breakers Circuit breakers are designed to flip over when too large a current flows

They break the circuit

Rely on magnetic forces

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Fuses & Earth Wire - Faults

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How Science Works

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Summary Questions

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Fuses Extra Questions

1. A short-circuit in an electrical cable or appliance happens if a live wire ……………… an earthed metal part or a neutral wire. When a short-circuit happens, the current in the live wire ……………… and ……………… the fuse wire in the appliance plug. When the fuse wire ………………, it causes a gap in the circuit which ……………… the live wire, so no current passes through the appliance any more.

2. The recommended fuse for the mains plug of a certain hairdryer is a 3 A fuse. When the hairdryer is used one day, the fuse melts.

3. What would happen if the fuse was replaced with a new 3 A fuse without repairing the hairdryer?

4. Why would it be dangerous to replace the fuse with a 5 A fuse or a 13 A fuse?

breaks cuts off melts rises touches

P2.4.1 Household Elect (Part B)

g) If an electrical fault causes too great a current, the circuit is disconnected by a fuse or a circuit breaker in the live wire.

h) When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit. i) Some circuits are protected by Residual Current Circuit Breakers (RCCBs).

J) Appliances with metal cases are usually earthed.

k) The earth wire and fuse together protect the wiring of the circuit.

P2.4.1 Household Elect (Part B)

g) If an electrical fault causes too great a current, the circuit is disconnected by a fuse or a circuit breaker in the live wire.

h) When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit. i) Some circuits are protected by Residual Current Circuit Breakers (RCCBs).

J) Appliances with metal cases are usually earthed.

k) The earth wire and fuse together protect the wiring of the circuit.

P2.4.1 Household Elect (Part B)

g) If an electrical fault causes too great a current, the circuit is disconnected by a fuse or a circuit breaker in the live wire.

h) When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit. i) Some circuits are protected by Residual Current Circuit Breakers (RCCBs).

J) Appliances with metal cases are usually earthed.

k) The earth wire and fuse together protect the wiring of the circuit.

P2.4.1 Household Elect (Part B)

g) If an electrical fault causes too great a current, the circuit is disconnected by a fuse or a circuit breaker in the live wire.

h) When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit. i) Some circuits are protected by Residual Current Circuit Breakers (RCCBs).

J) Appliances with metal cases are usually earthed.

k) The earth wire and fuse together protect the wiring of the circuit.