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Solved problems for the chapter:

Electric Fields and Force

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Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:electric_fields_and_force/4979/

Example 1.

Two charged bodies are placed 30 cm apart. They act on each other with an electric force. What happens to the magnitude of the electric force if we reduce the distance between the bodies?

The electric force remains the same.
The electric force decreases.
The electric force increases.

Example 2.

A negatively charged straw is lying on a table. What happens when we bring a negatively charged plastic rod close to it?

Two metal plates are attached to each other. One plate is charged with a large quantity of negative charge and the other with a large quantity of positive charge. A negatively charged metal ball hanging on a string is placed between them as shown in the figure below. What happens to the ball after it is allowed to fall?

Draw the lines of force around a:

positive point charge,
negative point charge.

A steel rod is negatively charged. Where is the electric charge located in the rod? Explain.

Draw the electric field lines between:

two negative charges.
positive and negative charges.

In each case, is an electric field present between the charges?

Identify the correct statements in the list below:

An electric force acts when charged bodies are in contact.
The electric force of a charge acts in the space around the charge.
No electric force exists between positive and negative charges.
An electric force acts at the centre of gravity of a body.
The higher the charge on a body, the greater the electrical force it exerts on other charged bodies around it.

When a charged body with a charge of magnitude and another with a charge of magnitude are placed together, an electric force acts between them. Is this force repulsive or attractive? Explain.

Two styrofoam beads are attached to strings and suspended freely as shown in the figure below. What can we say about the charge on the beads?

10.

A balloon is charged negatively by rubbing it against a woolen jacket. Why does the balloon stick to the wall if we place it against the wall? Note that the wall is electrically neutral.

11.

Describe how the electrosope works. What happens if we charge it with a negatively charged rod?

12.

Describe how we can charge conductors by induction. What happens to the charge on the bodies?

13.

Which statement describes the direction of an electric field at a point?

the direction of the force on a negative charge
the direction of the force on an N pole
the direction of the force on a positive charge
the direction of the force on an S pole

14.

Which diagram shows the electric field pattern and direction around a positive point charge?

15.

A negatively charged plastic rod P is placed above a positively charged plastic rod Q.

What are the directions of the electrostatic forces on rod P and on rod Q?

	electrostatic force on rod P	electrostatic force on rod Q
A	downwards	downwards
B	downwards	upwards
C	upwards	downwards
D	upwards	upwards

16.

Which diagram shows the electric field pattern around a positive charge?

17.

The diagrams represent two different electric fields.

A single electron is located in each of the fields. Which row gives the correct direction of the force on the electron and the field in which there is a larger force on it?

	direction of the force	larger force
A		field 1
B		field 2
C		field 1
D		field 2

18.

The diagram shows point X between two charged plates.

Which diagram shows the electric field pattern near point X?

19.

Which statement about electric charges is correct?

Like charges attract and unlike charges attract.
Like charges attract and unlike charges repel.
Like charges repel and unlike charges attract.
Like charges repel and unlike charges repel.

20.

Which diagram represents the electric field due to a negatively-charged conducting sphere?

21.

The diagrams each show a positive point charge. Which diagram represents the pattern and the direction of the electric field due to the charge?