Electric potential

This question is about lightning.

Sheet lightning occurs when there is an electrical discharge between the upper and lower regions of a thunder cloud. The upper regions are positive and the lower regions are negative.

The thunder cloud can be modelled as an ideal parallel plate capacitor with circular horizontal plates.

The data for the capacitor comes from the cloud.

The diagram shows the plates of the model capacitor superimposed on the cloud.

Draw on the diagram to show the electric field lines between capacitor plates.

Suggest why the actual electric field lines of the cloud would differ from what you have drawn.

Calculate the capacitance C of the model capacitor.

Assume the permittivity of the material of the cloud is the same as the permittivity of free space.

Calculate the magnitude of the charge Q on one of the plates of the model capacitor.

Fork lightning is an electrical discharge that occurs between the bottom of the cloud and the surface of the Earth.

Another cloud has a charge of 155 C and is at a height of 2.0 km.

The surface of the Earth has an electrical potential V of 0 V.

Assume the cloud acts as a point charge.

Calculate the magnitude of the electrical potential V between the cloud and the surface of the Earth.

A fork lightning strike has a duration of 25 ms. The cloud discharges at a constant rate. The cloud is uncharged after the strike.

Calculate the number of electrons reaching the ground in 1.0 ms.

The diagram below shows two oppositely charged spheres.

The magnitude of the charge on each sphere is the same. The point P is on the line joining the centres of the spheres and is the same distance from the centre of each sphere.

Which statement is correct?

A A negatively charged particle at P will move to the right.

B The direction of the electric field at P is to the left.

C The electric potential at P is zero.

D The magnitude of the electric field strength at P is zero.

Your answer

The diagram below shows the arrangement of the 3 protons inside the nucleus of lithium-6

The separation between each proton is about 1.0 × 10⁻¹⁵ m.

Calculate the magnitude of the repulsive electric force F experienced by the proton P

Explain how protons stay within the nucleus of lithium-6.

A spherical metal dome shown below is charged to a potential of −12 kV.

The dome is supported by a cylindrical plastic rod. The radius of the dome is 0.19 m.

Show that the magnitude of the total charge Q on the dome is 2.5 × 10⁻⁷ C.

The dome discharges slowly through the plastic rod. It takes 78 hours for the dome to completely discharge.

1 Show that the mean current I in the plastic rod is about 9 × 10⁻¹³ A.

2 The average potential difference across the plastic rod during discharge is 6000 V. The rod has cross-sectional area 1.1 × 10⁻⁴ m² and length 0.38 m.

Calculate the resistivity of the plastic.

=........ m

An electron is released at a distance r from the surface of a positively charged sphere. It is attracted towards the centre of the sphere and moves until it touches the surface.

Which of the following statements is/are correct?

1 The area under the F against r graph is equal to work done on the electron.

A Only 1

B Only 1 and 2

C Only 1 and 3

D 1, 2 and 3

Your answer

The structure of atoms was deduced in the early 1900s by Rutherford and his co-workers from the scattering of alpha-particles by a very thin sheet of gold.

Rutherford assumed that the scattering of the alpha-particles was due to electrostatic forces. Fig. 23 shows a detector used to record the number N of alpha-particles scattered through an

At = 0°, N was too large to be measured. The table below summarises some of the collected data.

/ °	lg (N)
150	1.5
75	2.3
60	2.7
30	3.9
15	5.1
0	N too large

Show that the number of alpha-particles scattered through 15° is about 4000 times more than those scattered through 150°.

Use the evidence from the table to explain the structure of the atom.

A proton with kinetic energy 0.52 MeV is travelling directly towards a stationary nucleus of cobalt-59 (⁵⁹₂₇Co) in a head-on collision.

Explain what happens to the electric potential energy of the proton-nucleus system.

Calculate the minimum distance R between the proton and cobalt nucleus.

Fig. 20.1 shows a positively charged metal sphere and a negatively charged metal plate.

On Fig. 20.1, draw a minimum of five electric field lines to show the field pattern between the

sphere and the plate.

Define electric potential at a point in space.

A metal sphere is given a positive charge by connecting its surface briefly to the positive terminal of a power supply. The electric potential at the surface of the sphere is + 5.0 kV. The sphere has radius 1.5 cm.