Chapter 22 - Electric Fields and Magnetism

Question 1

Define a field in physics.

Answer 1

A field is a region in which an object will experience a force at a distance.

Question 2

Define Electric Field Strength, in terms of Force.

Answer 2

The electric field strength of an electric field at a point in space is defined as the force experienced per unit positive charge at that point. Electric Field Strength, E, is:

E = F ÷ Q
Electric Field Strength = Force ÷ Positive Charge
NC⁻¹ = N ÷C

Question 3

Is Electric Field Strength vector or scalar?

Answer 3

Electric Field Strength is a vector quantity.

Question 4

Define an Electric Field.

Answer 4

An Electric Field is a field created by charged objects.

Question 5

What direction does an Electric Field travel?

Answer 5

An Electric Field travels from positive to negative, denoted by Electric Field lines.

Question 6

State Coulomb’s Law.

Answer 6

According to Coulomb’s Law, any two point charges exert and electrostatic (electrical) force on each other that is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

Question 7

What is the equation of Coulomb’s Law?

Answer 7

The equation of Coulomb’s Law.

F =  Qq / 4πε₀r²
Force = (Charge 1 x Charge 2) ÷ (4 x Pi x Permittivity of Free Space x radius²)
N = (C x C) ÷ (4 x πx C²N⁻¹m⁻² x m²)

Question 8

Define Electric Field Strength in terms of the radius of a sphere.

Answer 8

Electric Field Strength, E, at a distance, r, from the centre of the sphere is equal to the force F experienced by a positive ‘test’ charge divided by the charge q on the test charge. Therefore,

E = Q ÷4πε₀r²
Energy = Charge ÷(4 x Pi x Permittivity of Free Space x radius²)
NC⁻¹ = C ÷ (4 x πx C²N⁻¹m⁻² x m²)

Question 9

Describe Electric Field Strength in terms of Potential Difference.

Answer 9

The Electric Field Strength of Parallel Plates is defined as:

E = V ÷ d
Electric Field Strength = Potential Difference ÷Distance Between Plates.
Vm⁻¹ = V ÷m

Question 10

Define Capacitance in terms of Permittivity.

Answer 10

Capacitance is defined as:

C = εA ÷d
Capacitance = (Permittivity x Area) ÷distance between plates.
F = (C²N⁻¹m⁻² x m²) ÷ m

Question 11

Define Electric Potential Energy.

Answer 11

Electric Potential Energy is:

E = Qq ÷4πε₀r

Electric Potential Energy = (Charge 1 x Charge 2) ÷(4 x Pi x Permittivity of Free Space x Radius

J = (C1 x C2) x (4 x πx C²N⁻¹m⁻² x m)

Question 12

How do you conduct an experiment to detect an electrical field.

Answer 12

To detect an electrical field generated by an object:

• Momentarily charge the foil with the object (by touching them together.)
• Suspend a gold foil from an insulator next to the object.
• If the foil begins to repel from the object, the object will have an electric field.
• The closer the foil, the more it will repel.