IGCSE Online Tutorial - Jesmul Sir's Portal

# IGCSE Online Tutorial - Jesmul Sir's Portal

## Physics GCSE: Static and Current Electricity

Exam-Style Questions
1.      Two identical strips of nylon are charged with static electricity and hung from string so that they can swing freely.

a) How could they have been charged?

(1 mark)

b) If the two strips are brought near each other, what would happen?

(2 marks)

c) Static can be used in paint spraying. Powdered paint is blown out of the paint gun at high speed and rubs against the side of the gun.
All the powder has a positive charge. Why does the paint spread out into a fine spray?

(2 marks)

d) Why don't you have to turn the bicycle frame around?

(1 mark)

e) Why is so little of the paint wasted?

(1 mark)

f) Another factory makes microprocessor for computers. They don't want static to build up on the workers.

Why do they want to avoid static charge building up?

(2 marks)

g) The factory is to have a new carpet fitted. Explain why they should not choose a nylon carpet.

(1 mark)

(Marks available: 10)

Answer outline and marking scheme for question: 1

a) Rub the strips with a cloth of some kind.

(1 mark)

b) They would repel (push apart) because they have the same charge. A force of repulsion moves them apart.

(2 marks)

c) As they would have the same charge they would repel and would be trying to spread out as much as they could.

(2 marks)

d) The charged paint would be attracted around the back anyway.

(1 mark)

e) Paint doesn't miss the frame because it is attracted to it.

(1 mark)

f) Sparks from the static charge would damage the delicate components.

(2 marks)

f) Nylon carpets would easily get charged up.

(1 mark)

(Marks available: 10)

2.      a) A circuit is built with a bulb, a variable resistor and an Ammeter.
How does adjusting the variable resistor effect the brightness of bulb X?

(1 mark)

b) How does adjusting the variable resistor effect the reading on the Ammeter P?

(1 mark)

c) The variable resistor is replaced by a second bulb Y which is identical to bulb X.
If the battery supplies 6V, how much will the potential difference be across each of the bulbs?

(1 mark)

d) The bulbs both go out. Give two possible reasons for this.

(2 marks)

e) The circuit is repaired and is made into a parallel circuit with a third bulb.
If the reading on Ammeter Q is 3A, then how much current is passing through bulbs X and Y?

(2 marks)

f) What would be the reading on Ammeter P?

(1 mark)

g) Calculate the resistance of bulb Z.

(2 marks)

(Marks available: 10)

Answer outline and marking scheme for question: 2

a) The brightness will change.

(1 mark)

b) The reading will go up or down.

(1 mark)

c) Each bulb will have 3V across it.

(1 mark)

d) One of the bulbs is broken / A wire has come loose / The battery is running down.

(2 marks)

e) Two bulbs in series will have twice the resistance so the current will be half. 1.5A

(2 marks)

f) Ammeter P will read 4.5A (3A+ 1.5A)

(1 mark)

g) R=V/I. R=6V/3A=2 ohms

(2 marks)

(Marks available: 10)

3.      a) A kettle has a power rating of 2000W. It takes 6 minutes (0.1 hours) for it to boil the water when it is full.

What is the kettle's power rating in kiloWatts?

(1 mark)

b) How many units of electricity have been used?

(2 marks)

c) If each unit costs 6p, then how much does it cost to boil the water in the kettle?

(1 mark)

d) In an experiment Sasha coiled up a thin piece of Nichrome wire and placed it in a container of water. He turned on the electricity and measured to see if the water temperature was affected.

How would Sasha measure the electrical power going into the coil?

(2 marks)

e) In five minutes the temperature went up by 6 degrees centigrade. State 2 changes that Sasha could make to get a bigger temperature rise.

(2 marks)

f) At the same time, Sasha built another circuit that included a Thermistor.
The reading on the Ammeter was 0.2A. The thermistor was lowered into the water heated by the previous circuit. Explain in terms of current and resistance why the ammeter reading would change.

(2 marks)

(Marks available: 10)

Answer outline and marking scheme for question: 3

a) 2kW

(1 mark)

b) units used = 2kW x 0.1h = 0.2kWh

(2 marks)

c) cost = 0.2kWh x 6p = 1.2p

(1 mark)

d) Measure the current and the p.d. / Using an Ammeter and Voltmeter.

(2 marks)

e) Increase the supplied voltage. / Shorten the coiled up wire.

(2 marks)

f) If heated the resistance of the Thermistor lowers.

(1 mark)

As the resistance lowers more current will flow - higher meter reading.

(1 mark)

(Marks available: 10)

4.      a) Brian has bought an old metal lamp in a junk shop. He is trying to check the wiring. He opens the plug and finds the following:
What is wrong with the wiring in the plug?

(1 mark)

b) What danger would this wiring pose?

(2 marks)

c) Brian took apart his modern plastic lamp to see how to put the metal lamp right.

He could not find an earth wire. Why was one not fitted?

(2 marks)

d) The lamp plugs into the mains which provides 240V. If Brian fits a 60W bulb what current would be drawn?

(2 marks)

e) Should the plug have a 13A or a 3A fuse?

(1 mark)

f) Explain your choice and say whether it protects well enough.

(2 marks)

(Marks available: 10)

Answer outline and marking scheme for question: 4

a) The live wire is in the earth terminal and the earth wire in the live terminal.

(1 mark)

b) The live current would flow down the earth wire, which is connected to metal casing so there would be a risk of a shock.

(2 marks)

c) There are no exposed metal parts. (double insulated) / So no earth wire is needed.

(2 marks)

c) I=P/V

I=60W / 240V=0.25A

(2 marks)

d) A 3A fuse should be fitted.

(1 mark)

e) 3A is the lowest fuse rating available above the current drawn. 3A is a lot more than 0.25A so there could be a fault that might not blow the fuse.

(2 marks)

(Marks available: 10)