Page 136 - Physics Coursebook 2015 (A level)

Cambridge International AS Level Physics
End-of-chapter questions
1 Figure 8.4 on page 118 shows apparatus used to investigate the field between a pair of charged, parallel plates.
a Explain why the piece of gold foil deflects in the manner shown. [1]
b State and explain what would be observed if the gold foil momentarily touched the negatively
charged plate. [2]
2 A charged dust particle in an electric field experiences a force of 4.4 × 10−13 N. The charge on the
particle is 8.8 × 10−17 C. Calculate the electric field strength. [2]
3 Calculate the potential difference that must be applied across a pair of parallel plates, placed
4 cm apart, to produce an electric field of 4000 V m−1. [2]
4 A potential difference of 2.4 kV is applied across a pair of parallel plates. The electric field strength between the plates is 3.0 × 104 V m−1.
a Calculate the separation of the plates. [2]
b The plates are now moved so that they are 2.0 cm apart. Calculate the electric field strength
produced in this new position. [2]
5 A variable power supply is connected across a pair of parallel plates. The potential difference
across the plates is doubled and the distance between the plates is decreased to one-third of the
original. State by what factor the electric field changes. Explain your reasoning. [3]
6 Figure 8.17 shows a positively charged sphere hanging by an insulating thread close to an earthed metal plate.
metal plate
positively charged sphere
Figure 8.17 For End-of-chapter Question 6.
a Copy Figure 8.17 and draw five lines to show the electric field near the plate and the sphere. [3]
b Explain why the sphere is attracted towards the metal plate. [2]
c The sphere is now replaced with a similar negatively charged sphere.
i Explain what would be observed when the sphere is brought near to the earthed metal plate. [2]
ii Describe any changes to the electric field that would occur. [1]
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