10.1 Describing Fields

Which of the following best describes the direction of gravitational field lines around a massive object?

A. Radially outwards from the object

B. Radially inwards towards the object

C. Parallel to the surface of the object

D. Perpendicular to the surface of the object

The gravitational field strength at a distance r from the centre of a planet is g. What would be the gravitational field strength at a distance 2r from the centre?

A. g

B.g/2​

C. g/4​

D. 2g

Which of the following statements about electric field lines is FALSE?

A. They originate from positive charges and terminate at negative charges.

B. They never cross each other.

C. Their density represents the magnitude of the electric field.

D. They are always straight lines.

What is the electric field strength halfway between two equal and opposite point charges?

A. Zero

B. Equal to the field due to one of the charges

C. Double the field due to one of the charges

D. Infinite

How does the electric field strength vary with distance from an infinite plane of positive charge?

A. It remains constant.

B. It decreases linearly.

C. It decreases with the inverse square of the distance.

D. It increases with the inverse square of the distance.

a) A point mass M is placed at the origin of a coordinate system. Describe the pattern and direction of the gravitational field lines around this point mass. [2]

b) If a test mass m is placed at a distance r from the point mass M, calculate the gravitational field strength experienced by the test mass. [3]

a) Describe the difference in the electric field lines around a positive point charge and a negative point charge. [2]

b) For a point charge Q placed at the origin, calculate the electric field strength at a point located at a distance r from the charge. [3]

a) An infinite plane sheet has a uniform surface charge density sigma. Describe the behaviour and direction of the electric field lines above and below the sheet. [2]

b) Calculate the electric field strength due to the infinite plane sheet at any point above or below the sheet. [3]

a) Define the term 'gravitational field strength' at a point in space. [2]

b) Earth has a gravitational field strength of approximately 9.81 N/kg. If another planet has twice the mass of Earth but the same radius, what would be its gravitational field strength? [3]

c) How does the gravitational field strength vary as you move away from the surface of a planet? [2]

a) What is the significance of electric field lines crossing each other? [2]

b) Describe the electric field pattern around a positive and negative point charge placed close to each other. [3]

c) How does the electric field strength vary around an infinite plane sheet with a uniform charge density? [2]