Topic 7 - Electric and Magnetic Fields

Question 1

What is the relationship between flow of electrons and flow of current?

Answer 1

• Current flows in opposite direction to electrons

Question 2

What is an electric field?

Answer 2

• Region where charged particle experiences a non-contact force

Question 3

What is electric field strength?

Answer 3

• Force per unit charge experienced by object in electric field
• Constant in unifrom field
• Varies in radial field

Question 4

What is Coulomb’s law?

Answer 4

• Force between two point charges is directly proportional to prdocut of charges
• Force is inversely proportional to square of distance between charges

Question 5

What is electric potential?

Answer 5

Potential energy per unit charge of a positive point charge at that point in the field.

Question 6

What does the distance between field lines display?

Answer 6

Magnitude of force

Question 7

What are equipotential surfaces?

Answer 7

• Surface with equal electric potential at all points
• Therefore no work done on charge moving

Question 8

What is capacitance?

Answer 8

Charge stored per unit potential difference

Question 9

What does the area under a graph of charge against p.d represnt?

Answer 9

Energy stored by capacitor

Question 10

Explain the capacitor charging graphs for current, potential difference and charge against time

Answer 10

• Current: exponential decay
• Potnetial difference: exponential curve reaching same as terminal p.d
• Charge: excponential curve

Question 11

What is th area under a current against time charging graph equal to?

Answer 11

Charge

Question 12

What is the gradient on a charge against time charging graph equal to?

Answer 12

Current

Question 13

How do capacitors work?

Answer 13

• Capacitor connected to power supply
• Negative charge (electrons) build up on one side of the plate
• Electrons on other plate are repelled moving to positive terminal
• This created p.d and charge on both plates
• Current decreases as electrostatic repulsion increases

Question 14

Explain the capacitor discharging graphs for current, potential difference and charge against time

Answer 14

• All exponential decay curves

Question 15

What is the time constant?

Answer 15

• Product of resistance and capacitance
• Represents time taken to charge/discharge capacitor to a certain percentage of its max

Question 16

What is magnetic flux density?

Answer 16

• Measure of strength of magnetic field in Tesla
• Magnetic flux per unit area

Question 17

What is magnetic flux?

Answer 17

• Describes the magnetic field lines through a given area
• Φ = BA

Question 18

What is magnetic flux linkage?

Answer 18

• Magnetic flux multiplied by the number of turns