Page 381 - Physics Coursebook 2015 (A level)

Chapter 23: Coulomb’s law
2 Two parallel plates are 4cm apart and have a potential difference of 2.5kV between them.
a Calculate the electric field strength between the plates. [2]
b A small piece of dust carrying a charge of +2.4 nC moves into the space between the plates.
i Calculate the force on the dust particle. [2]
ii The mass of the dust particle is 4.2 μg. Calculate the acceleration of the particle towards the
negative plate. [2]
3 A small sphere carries a charge of 2.4 × 10−9 C. Calculate the electric field strength at a distance of:
a 2 cm from the centre of the sphere [2]
b 4 cm from the centre of the sphere. [2]
4 A conducting sphere of diameter 6.0 cm is mounted on an insulating base. The sphere is connected to a power supply which has an output voltage of 20 kV.
a Calculate the charge on the sphere. [3]
b Calculate the electric field strength at the surface of the sphere. [2]
5 The nucleus of a hydrogen atom carries a charge of +1.60 × 10−19 C. Its electron is at a distance of
1.05 × 10−10 m from the nucleus. Calculate the ionisation potential of hydrogen. [3] (Hint: This is equal to the work per unit charge needed to remove the electron to infinity.)
6 a Define electric field strength. [2] b Two charged conducting spheres, each of radius 1.0 cm, are placed with their centres 10 cm apart,
as shown in Figure 23.18.
Sphere A carries a charge of +2 × 10−9 C.
Figure 23.19 shows how the electric field strength between the two spheres varies with distance x.
x
sphere A sphere B
Figure 23.18 For End-of-chapter Question 6.
7.0 6.0 5.0 4.0 3.0 2.0 1.0
0 0 2.0
i Calculate the field produced by sphere A at the 5.0 cm mark. [2]
ii Use your result to b i to calculate the charge on sphere B. [3]
c i
ii Suggest and explain how the potential at the surface of sphere A would compare before and after
Sphere B is now removed. Calculate the potential at the surface of sphere A. [2] sphere B was removed. [2]
4.0 6.0 8.0 x / m × 10–2
Figure 23.19 Variation of electric field strength with distance x from the centre of sphere A.
369
E / V m–1 × 103