17) Current of Electricity

Question 1

Define current.

Answer 1

Current is the rate of flow of charges.

Question 2

What is the SI unit of current?

Answer 2

Ampere (A)

Question 3

What is the instrument used to measure current in a circuit?

Answer 3

Ammeter

Question 4

What is the relationship between I, Q and t?
(in other words the formula)
[Please recall what I, Q and t represents]

Answer 4

Q = It

Question 5

How should the ammeter be connected in a circuit?

Answer 5

connected in series

Question 6

Define electromotive force (e.m.f.).

Answer 6

Electromotive force (e.m.f.) is the amount of work done by a source (e.g. battery, cell) in driving a unit charge around a complete circuit.

Question 7

Define potential difference (p.d).

Answer 7

Potential difference (p.d.) across a component in a circuit is the work done to drive a unit of charge through the component.

Question 8

What is the SI unit of electromotive force (e.m.f.)?

Answer 8

Volt (V)

Question 9

What is the SI unit of potential difference (p.d)?

Answer 9

Volt (V)

Question 10

What is the instrument used to measure voltage across a component in a circuit?

Answer 10

voltmeter

Question 11

What is the relationship between V, W and Q?
(in other words the formula)
[Please recall what V, W and Q represents]

Answer 11

W = VQ

Question 12

How should the voltmeter be connected in a circuit?

Answer 12

connected in parallel to the component

Question 13

Define resistance.

Answer 13

Resistance of a component is the ratio of voltage to current in a component.

Question 14

What is the relationship between R, V and I?
(in other words the formula)
[Please recall what R, V and I represents]

Answer 14

R = V / I

Question 15

What is the SI unit of resistance?

Answer 15

ohm (Ω)

Question 16

What are the factors that affect the resistance of a wire?

[There are 4 factors.]

Answer 16

1) length of wire (l)
2) cross-sectional area of wire (A)
3) resistivity of the material (ρ)
4) temperature of wire

Question 17

Define Ohm’s Law.

Answer 17

Ohm’s law states that the current through a metallic conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and other physical conditions remains constant.

Question 18

Explain why the filament lamp does not obey Ohm’s law.

Answer 18

As current flows through the filament lamp, it heats up and increases the resistance of the filament lamp.

Question 19

What are the 2 factors on a VI graph that shows an electrical component obeys Ohm’s law?
(i.e. what are the 2 things to look out for in a VI graph?

Answer 19

1) The graph must be a straight line.

2) The line must pass through the origin.

Question 20

State how the length of wire affects the resistance.

Answer 20

The longer the wire, the larger the resistance.

Question 21

State how the thickness of wire affects the resistance.

thickness also means cross-sectional area of wire

Answer 21

The thicker the wire, the lower the resistance.

The thinner the wire, the higher the resistance.

Question 22

State how temperature of a wire affects its resistance.

Answer 22

The higher the temperature, the larger the resistance.

Question 23

State the formula to find the total resistance of resistors connected in series.

Answer 23

Rt = R1 + R2 + R3

Question 24

State the formula to find the total resistance of resistors connected in parallel.

Answer 24

1/Rt = 1/R1 + 1/R2 + 1/R3