4.3 Uniform electric fields

Question 1

What can be said for most of the lines of force in a uniform electric field

Answer 1

The electric lines of force are equally spaced except around the edges but usually, we deal with the area where the lines of force are equally spaced

Question 2

When you move a charged object in a uniform electric field, how does the force vary

Answer 2

The force remains constant; E = F/Q and the value of E is the same everywhere in a uniform electric field

Question 3

What is the method of demonstrating a uniform electric field

Answer 3

• cut a small strip of aluminium foil
• attach it to the bottom of an uncharged insulating rod
• hold the rod vertical and lower the end with the foil into the space with the charged plates
• move the ruler so the foil is at different positions between the charged plates
  if the field is uniform the force on the foil will be constant

Question 4

What is a more direct way of showing a uniform electric field

Answer 4

• apply a p.d to two metal plates dipped in insulating liquid
• sprinkle thread onto the liquid and they will line up end to end to show the shape of the field

Question 5

For a uniform electric field what is another equation for the electric field strength

Answer 5

E = V/d

V is the electric potential between the two plates and d is the distance

Question 6

There are two ways of charging objects meaning there are two ways of producing electric fields, what are these ways

Answer 6

charging by frictional contact and charging by using a battery or d.c supply

Question 7

Define equipotential lines

Answer 7

Where the electric field is perpendicular to the lines along which the voltmeter readings are constant

Question 8

What is the work done in moving a charged object along an equipotential line

Answer 8

Zero

Question 9

How do you calculate the work done in moving a charged object between two equipotential lines

Answer 9

change in work done = charge x change in voltage

Question 10

What are the charges of the upper atmosphere and the earth’s surface and what is the direction of the field

Answer 10

the upper atmosphere carries a permanent positive charge and the earth’s surface carries a permanent negative charge. The field is directed downwards towards the earth’s surface