Electric Charge

4.2.1 Electric Charge - Electric Fields

An electric field is a region of space around an electric charge where another electric charge will experience a force. It's a fundamental concept in understanding how electric charges interact.

What is an Electric Field?

Imagine an electric charge placed in space. This charge creates an invisible area around it – that's the electric field. This field exerts a force on any other electric charge that enters this region.

How Electric Fields are Created

Electric fields are created by electric charges. The magnitude and direction of the electric field depend on the magnitude and sign of the charge creating the field, and the distance from the charge.

Electric Field Lines

Electric field lines are a visual way to represent an electric field. They show the direction of the electric field at any point in space.

• Electric field lines originate from positive charges and terminate on negative charges.
• The closer the field lines are to each other, the stronger the electric field.
• The direction of the electric field at any point is tangent to the electric field line at that point.

Force on a Charge in an Electric Field

When a charge enters an electric field, it experiences a force. The direction of this force depends on the sign of the charge:

• Positive charge: A positive charge experiences a force in the same direction as the electric field.
• Negative charge: A negative charge experiences a force in the opposite direction to the electric field.

Mathematical Representation

The electric field, E, is a vector quantity. It is defined as the force per unit charge experienced by a test charge placed at a point in the field.

$$ \mathbf{E} = \frac{F}{q} $$

Where:

• E is the electric field vector (in N/C).
• F is the electric force vector (in Newtons).
• q is the magnitude of the test charge (in Coulombs).

The electric force, F, on a charge q in an electric field E is given by:

$$ \mathbf{F} = q\mathbf{E} $$

Example: Electric Field around a Positive Charge

Consider a positive point charge. The electric field lines radiate outwards from the positive charge. If a positive test charge is placed in this field, it will experience a force in the same direction as the field lines (away from the positive charge).

Example: Electric Field around a Negative Charge

Now consider a negative point charge. The electric field lines radiate inwards towards the negative charge. If a positive test charge is placed in this field, it will experience a force in the opposite direction to the field lines (towards the negative charge).

Summary

An electric field is a region of space where an electric charge experiences a force. Electric field lines visualize the direction of the field. The force on a charge in an electric field is directly proportional to the magnitude of the electric field and the magnitude of the charge.

Concept	Description
Electric Field	Region of space where a charge experiences a force.
Electric Field Lines	Lines that show the direction of the electric field.
Force on a Charge	The force experienced by a charge in an electric field, dependent on the field strength and charge magnitude.