Electrodynamics

Question 1

Faraday’s law

Answer 1

The emf induced is directly proportional to the rate of change of magnetic flux (flux linkage).

Question 2

AC

Answer 2

Alternating current. Current which reverses direction periodically.

Question 3

Commutator

Answer 3

A device which ensures that the direction of the current in a coil is reversed every half revolution.

Question 4

Conventional current

Answer 4

The rate of flow of positive charge from the positive terminal of the cell to the negative terminal.

Question 5

DC

Answer 5

Direct current. Current flowing in one direction only.

Question 6

Electromagnetic induction

Answer 6

Occurs when a current is induced in a closed conducting loop when there is a change in the magnetic flux passing through the surface area of the conducting loop.

Question 7

Induced emf

Answer 7

The total amount of electrical energy supplied per unit positive charge.

Question 8

Magnetic fields

Answer 8

Produced by magnets or by moving electrical charges. Magnetic field lines are drawn to represent the direction of the magnetic field at a point. The symbol for magnetic field is B and its unit is the Tesla (T).

Question 9

Magnetic flux density

Answer 9

A representation of the magnitude and direction of the magnetic field.

Question 10

Magnetic flux

Answer 10

The product of the magnetic field (B) and the cross-sectional area (A) that the field lines pass through in an enclosed loop:Φ = BAcosθ

Question 11

Magnetic flux linkage

Answer 11

The product of the number of turns on a coil and the flux through a coil (NФ).

Question 12

Lenz’s law

Answer 12

The induced current flows in a direction so as to set up a magnetic field to oppose the change in magnetic flux.

Question 13

Diode

Answer 13

A component that only allows current to flow in one direction.

Question 14

Generator

Answer 14

A device which converts mechanical energy into electrical energy.

Question 15

Motor

Answer 15

A device which converts electrical energy into mechanical energy.

Question 16

What is the purpose of a split-ring commutator

Answer 16

To keep the torque on a DC motor from reversing every time the coil moves through the plane perpendicular to the magnetic field, a split-ring device called a commutator is used to reverse the current at that point.

Question 17

What do motors do?

Answer 17

Convert electrical energy into mechanical energy.

Question 18

What does a generator?

Answer 18

Convert mechanical energy into electrical energy

Question 19

Function of a diode

Answer 19

The most common function of a diode is to allow an electric current to pass in one direction (called the diode’s forward direction), while blocking it in the opposite direction (the reverse direction).

Question 20

Factors which affect the power of motor

Answer 20

Increasing the strength of the magnetic field
Increasing the strength of the current through the coils
Increasing the number of windings in the coils
Wrapping the coil around an iron ore
Using several coils wound at slightly different angles on the armature.

Question 21

How to increase induced emf of AC generator

Answer 21

Increase magnetic field strength
Increase enclosed surface area of conducting loop
Used curved magnets (Keep coil moving perpendicular)
Rotate coil/loop at a faster rate
Increase number of windings

Question 22

How does a transformer work?

Answer 22

Alternating current is sent to the primary coil by applying an AC voltage across the primary
coil.
This alternating current will cause a change in the magnetic field around the conductor
wound around the primary coil.
The change in magnetic field aroung the primary coil will cause a change in the magnetic flux
experienced by the secondary coil.
According to Lenz’s Law: The induced emf in the secondary coil will be of such a nature as to
induce a current within the secondary coil that forms a magnetic field to oppose the change
experienced in magnetic flux.
The input power and the output power will ALWAYS be equal in magnitude.

Question 23

Advantage of AC

Answer 23

AC voltages can be stepped up or down using transformers.
AC voltages can be stepped up and electrical power can be transmitted over long distances
in power lines at low current to minimize the power loss due to heating.
It is easier and cheaper to convert AC to DC.
AC motors can produce a higher power output than DC motors.