4.1 and 4.2 - Electricity: Charge, Current, Energy, Power and Resistance

Question 1

Current

Answer 1

The rate of flow of charged particles

The product when 1 C passes through a component in 1 second

Question 2

Charge

Answer 2

Q = It

1 Coloumb is the charge that flows past a point in one second when there is a current of 1 Amp.

Question 3

Kirchhoff’s First Law

Answer 3

The sum of the charges flowing INTO a circuit junction must be equal to the sum of the charges leaving it.

Question 4

Conductors

Answer 4

A substance that contains a very large number of free conduction electrons per unit volume.

Question 5

Insulators

Answer 5

A substance that contains very few free conduction electrons per unit volume.

Question 6

Semiconductors

Answer 6

A substance that have values of ‘n’ (number of free conduction electrons per unit volume) between those of conductors and insulators.

Question 7

e.m.f. (electromotive force)

Answer 7

The energy GAINED per unit charge by charges passing through the supply, when a form of energy is transferred to ELECTRICAL ENERGY carried by the charges. Measured in Volts (V) / Joules per Coulomb (JC-1)

Question 8

p.d. (potential difference)

Answer 8

The energy TRANSFERRED per unit charge by the charges passing through the component (transfers electrical energy into other forms). Measured in Volts (V) or Joules per Coulomb (JC-1).

Question 9

Ohm’s Law

Answer 9

States that the CURRENT through a conductor is DIRECTLY PROPORTIONAL to the POTENTIAL DIFFERENCE across it, provided that physical conditions, such as temperature, remain CONSTANT.

Question 10

Graph of Ohm’s Law (I-V)

Answer 10

A proportional, straight line graph.

Question 11

Graph of Resistance against Length

Answer 11

Proportional

Question 12

Graph of Resistance against Cross Sectional Area

Answer 12

Reciprocal

Question 13

Graph of Resistance against Temperature for a METAL WIRE (conductor)

Answer 13

Proportional but the line doesn’t start from 0.

Question 14

Graph of Resistance against Temperature for a THERMISTOR (semiconductor)

Answer 14

Reciprocal but the line touches on the y-axis

Question 15

I-V graph of a resistor at constant temperature

Answer 15

Ohm’s Law graph (proportional)

Question 16

I-V graph of a filament lamp

Answer 16

CUBIC. However, at one point, the lamp does show Ohm’s Law but then curves and plateaus.

Question 17

I-V graph of a Diode/LED

Answer 17

INFINITE RESISTANCE (line touches zero) then instantaneous decrease in resistance (line goes up)

Question 18

I-V graph of a Thermistor

Answer 18

Reciprocal

Question 19

I-V graph of a LDR

Answer 19

Line touches the y-axis and then slopes downards reciprocally.

Question 20

Resistivity

Answer 20

p = RA/l

The ratio of the product of resistance and cross-sectional area of a component and its length.

Question 21

Name each variable of the following equation:

Pt = Po [1 + a(T-To)]

Answer 21

Pt = resistivity of the material at a temperature, T
Po = restivity value that is quoted at To (usually 20 C)
a = temperature coefficient
T = temperature of material
To = reference temperature at which the resistivity of material is quoted (20 C / 293 K)

Question 22

Power

Answer 22

The rate at which energy is transferred from one form to another.

Question 23

Kilowatt-Hour (kWh)

Answer 23

1000 watts for 3600 seconds (3 600 000 J)