Electric Fields

Question 1

How does electrostatic force vary with distance?

Answer 1

Inverse square law (∝ 1/r²).

Question 2

What assumption can be made about air when calculating electrostatic force?

Answer 2

Air can be treated as a vacuum.

Question 3

For a charged sphere, where can the charge be assumed to act?

Answer 3

At the centre.

Question 4

Compare gravitational and electrostatic forces between subatomic particles.

Answer 4

Electrostatic force is much stronger.

Question 5

How are electric fields represented?

Answer 5

By electric field lines

Question 6

What do electric field lines show?

Answer 6

The direction of force on a positive test charge.

Question 7

Define electric field strength.

Answer 7

Force per unit charge at a point in a field.

Question 8

What is a uniform electric field?

Answer 8

A field where field lines are parallel and equally spaced.

Question 9

Where is a uniform electric field produced?

Answer 9

Between parallel plates.

Question 10

What is the trajectory of a charged particle entering a uniform field at right angles?

Answer 10

Parabolic.

Question 11

Why is the motion parabolic?

Answer 11

Constant force causes constant acceleration perpendicular to motion.

Question 12

What type of field surrounds a point charge?

Answer 12

A radial field.

Question 13

Define absolute electric potential.

Answer 13

Work done per unit charge in bringing a charge from infinity to a point.

Question 14

Where is electric potential zero?

Answer 14

At infinity.

Question 15

What are equipotential surfaces?

Answer 15

Surfaces of constant electric potential

Question 16

How much work is done moving a charge along an equipotential surface?

Answer 16

Zero.

Question 17

How does V vary with r?

Answer 17

Inverse relationship (∝ 1/r).

Question 18

How does E vary with r in a radial field?

Answer 18

Inverse square relationship (∝ 1/r²).

Question 19

What does the area under a graph of E against r represent?

Answer 19

Change in electric potential (ΔV).