Electric and Magnetic Fields

Question 1

What is a force field?

Answer 1

A region in which a non-contact force is experienced by a corresponding-interacting particle

Question 2

What is an electric field?

Answer 2

A region in which a charged particle will experience a non-contact force

Question 3

What is electric field strength?

Answer 3

The force per unit charge experienced by a charged particle when placed at a specific point in the field

Question 4

State the equation used to find the force a charged particle experiences in an electric field?

Answer 4

F = EQ
Force = Electric Field Strength x Charge

Question 5

Which law determines the magnitude of the electric force between two charges?

Answer 5

Coulomb’s Law

Question 6

State Coulomb’s Law in words.

Answer 6

The force between two charges is directly proportional to the product of their charges and inversely proportional to the square of their separation

Question 7

State Coulomb’s Law equation.

Answer 7

F = kQ₁Q₂ / r²
where k = 1/4πε₀

Question 8

Describe the electric field pattern around a positive point charge.

Answer 8

A radial field, acting outwards

Question 9

Describe the electric field pattern around a negative point charge.

Answer 9

A radial field, acting inwards

Question 10

Describe the uniform electric field between two parallel plates.

Answer 10

Straight lines moving from the positive plate to the negative one, equally spaced

Question 11

What equation is used to calculate the electric field strength between two parallel plates?

Answer 11

E = V /d
Electric Field Strength = Potential Difference / Separation

Question 12

What is electric potential?

Answer 12

The amount of energy required to move a positive test charge from infinity to a given point in an electric field

Question 13

How do you calculate the electric potential for a radial field?

Answer 13

V = kQ/r
where k = 1/4πε₀

Question 14

What are equipotentials?

Answer 14

Lines in an electric field that have the same electric potential

Question 15

How do you calculate the work done in moving a charge along an equipotential?

Answer 15

No work is done since the electric potential doesnt change, therefore no force is acting

Question 16

What is ε₀?

Answer 16

Permittivity of free space ε₀ = 8.85 × 10−12 F m−1

Question 17

What does a capacitor do?

Answer 17

It stores charge in a circuit

Question 18

What two factors determine how much charge can be stored by a capacitor?

Answer 18

1. Potential Difference across the capacitor
2. Capacitance

Question 19

What is capacitance?

Answer 19

A measure of how much charge can be stored by a capacitor per unit potential difference across it

Question 20

State the equation used to calculate capacitance.

Answer 20

Q=CV —-> C = Q/V
Capacitance = Charge / P.d

Question 21

What is the unit of capacitance?

Answer 21

Farads (F), CV⁻¹

Question 22

What is represented by the area under a capacitor’s charge - potential difference graph?

Answer 22

The energy stored by the capacitor

Question 23

What is the represented by the gradient of a capacitor’s charge - potential graph?

Answer 23

The capacitance of the capacitor

Question 24

What are 3 equations to work out the energy stored by a capacitor?

Answer 24

W = 1/2 QV
W = 1/2 CV²
W = 1/2 Q²/C

Question 25

Describe a charge-time graph for charging a capacitor, what does the gradient represent?

Answer 25

The charge increases rapidly to start with and then exponentially increases by a smaller amount. The gradient = Q/t = current

Question 26

Describe a current-time graph for charging a capacitor, what does the area represent

Answer 26

It decreases dramatically do start with (looks like a y = 1/x graph)Area = It = charge

Question 27

Describe a voltage-time graph for charging a capacitor?

Answer 27

Increases dramatically to start with and then drops off

Question 28

What value is the product of the resistance and capacitance?

Answer 28

RC = τ (tau) the time constant

Question 29

What does the time constant tell you?

Answer 29

The time it takes for the capacitor to reach 63% of its full charge and the time taken for it to discharge to 37% of its full-charge