A LevelPhysicsEdexcelTopic Questions7. Electric & Magnetic FieldsCapacitance

Capacitance (Edexcel A Level Physics)

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1a
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The properties of capacitors make them useful in timing circuits.

The following circuit is used to provide an input Y to an integrated circuit.

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Initially, the capacitor is uncharged. The switch S1 is closed.

 

Sketch a graph to show how the potential at point Y varies with time.

q15a-nov-2020-9ph0-01-edexcel-as-a-level-phy

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1b
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When the potential at Y is 8.0 V, the switch S2 is closed.

i)
Calculate the time taken for the potential at Y to decrease to 2.0 V.

(3)





Time taken = ......................................................

ii)
Calculate the energy stored on the capacitor when the potential at Y is 2.0 V.

(2)




Energy stored = ......................................................

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1c
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When the potential at Y is 2.0 V, the switch S2 is opened.

Calculate the power dissipated by the resistance R1 when the potential at Y is 2.0 V.





Power dissipated = ......................................................

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2a
Sme Calculator3 marks

A ‘Gauss gun’ can be made from five ball bearings of equal mass and two magnets, as shown.

q18a-paper-1-june-2018-edexcel-a-level-physics

Pairs of ball bearings are placed to the right of two strong magnets. A single ball bearing is released from the left, as shown. The ball bearing is attracted to, and collides with, the first magnet. This and all subsequent collisions can be assumed to be elastic.

Explain what happens to make the last ball bearing on the right subsequently move off with a large velocity.

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2b
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A student set up the apparatus shown to measure the speed of the last ball bearing.
The ‘Gauss gun’ was placed at the end of a bench, so that the ball bearing left the gun and broke two strips of metal foil which formed part of an electric circuit.

q18b-june-2018-9ph0-01-edexcel-as-a-level-phy

As the ball bearing left the gun, it broke the first foil strip at its centre so that the capacitor started to discharge. When the ball bearing broke the second foil strip the capacitor discharge stopped.

i)
Calculate the energy stored in the capacitor when it was fully charged.

(2)




Energy stored = ................................

ii)
The voltmeter reading halved in the time taken for the ball bearing to travel between the two foil strips.

Show that the time taken for the ball bearing to travel between the two foil strips was about 0.1 s.

(2)

iii)
The two foil strips were 0.50 m apart.

Calculate the horizontal velocity of the ball bearing.

(2)




Horizontal velocity = ..................................

iv)
The student positioned the second foil strip with its centre 8.0 cm lower than the centre of the first foil strip.

Deduce whether the ball bearing broke the second foil strip at its centre.

Assume the ball bearing was travelling horizontally as it broke the first foil strip.

(2)

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1a
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The diagram shows two parallel metal plates with a potential difference (p.d.) of 100 V across them. Three equipotential lines are shown.

q13-nov-2021-9ph0-01-edexcel-as-a-level-phy

Draw lines to represent the electric field in the shaded area.

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1b
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A parallel plate capacitor consists of a thin layer of insulator of thickness d between two plates of conducting material of area A.

q13b-nov-2021-9ph0-01-edexcel-as-a-level-phy

The capacitor has a capacitance 0.1 μF and is charged to a p.d. of 100 V by connecting it to an electrical supply.

The capacitor is then disconnected from the supply and the p.d. between the two plates slowly decreases. This is because the insulator is not perfect and a small charge can flow through it.

The graph shows how the p.d. varies with time.

q13b-1-nov-2021-9ph0-01-edexcel-as-a-level-phy

The insulator is a type of plastic and should have a resistivity greater than 1014 Ω m.

Deduce whether the plastic used in this capacitor has a resistivity greater than this value.
A = 5.6 × 10−3 m2
d = 0.6 × 10−6 m

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