Electricity

Question 1

Back EMF

Answer 1

EMF induced in the spinning coil of an electric motor or in any coil in which the current is changing (e.g. the primary coil of a transformer). A back EMF acts against the change of applied pd.

Question 2

Charge carriers

Answer 2

Charged particles that move through a substance when a pd is applied across it

Question 3

Circuit rule for current (Kirchhoffs 1st Law)

Answer 3

1. The current passing through two or more components in series is the same through each component.
2. At a junction, the total current in = the total current out

Question 4

Circuit rules for PD (Kirchhoffs 2nd law)

Answer 4

1. For two or more components in series, the total pd across all the components is equal to the sum of the pd’s across each component.
2. The sum of the emf’s round a complete loop in a circuit = The sum of the pd’s round the loop.

Question 5

critical temperature of a superconducting material

Answer 5

temperature at and below which its resistivity is zero.

Question 6

electrical conductor

Answer 6

an object that can conduct electricity

Question 7

electrically insulating materials

Answer 7

an electrical insulator is a material that cannot conduct electricity; a thermal insulator is a material that is a poor conductor of heat

Question 8

electrolysis

Answer 8

process of electrical conduction in a solution or molten compound due to ions moving to the oppositely charged electrode

Question 9

electrolyte

Answer 9

a solution or molten compound that conducts electricity

Question 10

electromotive force (emf)

Answer 10

the amount of electrical energy per unit charge produced inside a source of electrical energy

Question 11

free electrons

Answer 11

electrons in a conductor that move about freely inside the metal because they are not attached to a particular atom.

Question 12

Internal resistance

Answer 12

Resistance inside a source of electrical energy; the loss of pd per unit current in the source when current passes through it

Question 13

Light dependent resistor (LDR)

Answer 13

Resistor which is designed to have a resistance that changes with the light intensity

Question 14

Negative Temperature coefficient

Answer 14

The resistance of a semiconductor decreases when its temperature is increased

Question 15

Ohm’s Law

Answer 15

The pd across a metallic conductor is proportional to the current as long as the physical conditions do not change

Question 16

Positive Temperature Coefficient

Answer 16

The resistance of a metal increases when its temperature is increased

Question 17

Potential Difference

Answer 17

The work done or energy transfer per unit charge between two points when charge moves from one point to the other

Question 18

Potential Divider

Answer 18

Two or more resistors in series connected to a source of pd

Question 19

Resistance

Answer 19

pd/current

Question 20

Resistivity

Answer 20

Resistance per unit length x area of cross section

Question 21

semiconductor

Answer 21

substance in which the number of charge carriers increases when the temperature is raised

Question 22

simple electric motor

Answer 22

electric motor with an armature consisting of a single coil of insulated wire

Question 23

superconductor

Answer 23

material that has zero electrical resistance

Question 24

thermistor

Answer 24

resistor which is designed to have a resistance that changes with temperature