Electric Current

Question 1

The Coulomb (C)

Answer 1

The total charge (Q) supplied by a current of 1A in the time (t) of one second.

Question 2

The Volt (V)

Answer 2

The energy per unit charge.

Question 3

Potential Difference (V)

Answer 3

The electrical energy (J) transferred per unit charge (C) when the electrical energy is converted into another form of energy.

Question 4

Electromotive Force (e.m.f., V)

Answer 4

The amount of energy supplied per unit charge.

Question 5

Internal Resistance

Answer 5

The source of emf has an inherent resistance to current flow termed internal resistance.

Question 6

Resistance (Ω)

Answer 6

Defined as the ratio of Potential Difference to Current, as in the equation V/I.

Question 7

The Ohm (Ω)

Answer 7

The current through a conductor is proportional to the potential difference across it provided the physical conditions remain constant.

The constant of proportionality is termed Resistance whose SI unit is known as the Ohm.

Question 8

Resistivity (Ωm)

Answer 8

Is given by the equation ρ = R A / l where R is resistance, A is cross-sectional area and is l length. Easier to recall as Resistivity = ρ l /A.

Question 9

Kilowatt-hour (KWh)

Answer 9

Is a unit of energy defined as 1000 watts for 3600 seconds, or kW x h (kWh).

Question 10

Kirchoff’s First Law (not 2nd law, so must be Current, or 1 looks like I)

Answer 10

The sum of the currents entering any junction is always equal to the sum of the currents leaving the junction.

Question 11

Kirchoff’s Second Law (not Seccond = Ccurrent as for Flemings Hand rules)

Answer 11

In any closed loop circuit, the sum of the emf’s is equal to the sum of the potential differences (pd’s).

The conservation of energy when applied to electricity provides this law. Recall that emf is the energy per unit charge (J/Q) transferred into electrical energy. The charge cannot return to the emf source with surplus energy otherwise it would grow each time.