Definitions 6.1+

Question 1

Capacitance

Answer 1

The quantity of charge which can be stored per unit potential difference across the plates of the capacitor.

Question 2

Farad

Answer 2

Equivalent to one coulomb per volt

Question 3

Exponential Decay

Answer 3

The quantity decreases at a rate that is proportional to the magnitude of the quantity at that time.

Question 4

Time constant

Answer 4

The time it takes for the charge remaining on a capacitor to decrease to 37% (1/e) of its initial value.

Question 5

Electric field

Answer 5

The region around a body in which other charged bodies will feel a force due to the electric charge of the body.

Question 6

Electric field lines

Answer 6

Show the shape of the field and the direction of the field line at a point in the direction in which a small positive charge would move when placed at that point.

Question 7

Electric field strength

Answer 7

Force per unit positive charge (N/C) or (V/m)

Question 8

Coulombs law

Answer 8

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

Question 9

Permittivity of free space

Answer 9

Physical constant related to the size of the force between electrical charges in free space (a vacuum). It has the value 8.85 x 10^-12 (C^2 m^-2 N^-1)

Question 10

Permittivity

Answer 10

A constant related to the size of the capacitance of a capacitor.

Question 11

Relative permittivity

Answer 11

Is the factor by which the capacitance of a capacitor with that material between its plates is increased relative to the capacitance of a capacitor with air or vacuum between its plates.

Question 12

Electric potential

Answer 12

Work done per unit positive charge to move that charge from infinity to a point in an electric field.

Question 13

Electrical potential energy

Answer 13

Work done to move that charge from infinity to a point in an electric field.

Question 14

Magnetic field

Answer 14

Region around a permanent magnet or moving charge in which another body with magnetic properties will feel a force.

Question 15

Magnetic field lines

Answer 15

Show the shape and the direction. The direction of the field line at a point shows the direction in which a plotting compass would point.

Question 16

Magnetic flux

Answer 16

Product of magnetic flux density and the area at right angles to the flux.Φ=BAcosθ

Question 17

Magnetic flux density

Answer 17

A measure of strength of the magnetic field.

Question 18

One weber (Wb)

Answer 18

Is the magnetic flux when a magnetic field of magnetic flux density one tesla passes at right angles through an area of one square metre.

Question 19

Fleming’s left hand rule

Answer 19

Shows the direction of the force on a conductor carrying a current in a magnetic field.

Question 20

Velocity selector

Answer 20

A device using perpendicular magnetic and electric fields to select charged particles travelling at a specific velocity which leave the region of crossed fields undeflected.

Question 21

Electromagnetic induction

Answer 21

Process of inducing an e.m.f in a conductor when there is a change in magnetic flux linkage across the conductor.

Question 22

Induced e.m.f

Answer 22

Is the e.m.f produced by electromagnetic induction

Question 23

Magnetic flux linkage

Answer 23

The product of the magnetic flux through the coil and the number of turns on the coil. Magnetic flux linkage = NΦ

Question 24

Faraday’s Law

Answer 24

The magnitude of the induced e.m.f is equal to the rate of change of flux linkage.

Question 25

Lenz’s law

Answer 25

States that the direction of any induced e.m.f or induced current is in a direction that opposes the flux change that causes it.

Question 26

Search coil

Answer 26

A small, flat coil used to determine the strength of a magnetic field.

Question 27

Generator

Answer 27

Device used to generate electricity, in which the work done to turn the coil with the magnetic field is transferred to electrical energy. The rotation of a coil within a magnetic field produces a constantly changing flux linkage through the coil. This in turn produces a constantly changing e.m.f. in the coil.

Question 28

Alternating current (a.c.)

Answer 28

Electrical current that reverses its direction with a constant frequency.
e.g. UK mains supply is a.c. with a frequency of 50Hz

Question 29

Transformer

Answer 29

Device that can either increase or decrease the size of an alternating voltage with little loss of power.

Question 30

Efficiency

Answer 30

The ratio of useful output energy to total input energy, useful energy expressed as a percentage.
(useful output energy ÷ total input energy) x 100%