Current of electric

Question 1

Define electric current

Answer 1

Electric current is the rate of flow of charged particles.

Question 2

State drift velocity formula

Answer 2

I = nAvq
n = no. of charge carriers per unit volume
A = cross sectional area of conductor
v = drift velocity
q = charge by each charge carrier

Question 2

Define charge

Answer 2

Charge is the product of current and time, if the current is steady.
(Q = It )

Question 3

Define potential difference

Answer 3

The potential difference across a device is the electrical energy converted to other forms of energy per unit charge passing through the device.
( V = W/Q )

Question 3

Define electromotive force

Answer 3

Electromotive force of a source is the electrical energy, converted from other forms of energy per unit charge, transferred by the source in driving unit charge round a complete circuit.

Question 4

Define power

Answer 4

Power is the rate at which work is done.

Question 5

Define resistance *

Answer 5

Resistance of a conductor is the ratio of the potential difference across the conductor to the current flowing through it.
( R = V/I )

Question 5

Ohm’s Law

Answer 5

Ohm’s Law states that the current I through a metallic conductor is proportional to the potential difference V across its ends under constant physical conditions.

Question 5

State power equations

Answer 5

P = dW / dt
P = IV
P = I²R (power loss)
P = V²/R

Question 6

Ohmic conductor I-V graph (y x)

Answer 6

It is a characteristic straight line passing through origin.
Since I increases proportionately with V, ratio V/I is constant, resistance is constant.

Question 7

Filament lamp I-V graph

Answer 7

It is a characteristic S-shaped curve that passes through the origin.
(line extend top right and bottom left to X infinity)

Question 8

Semiconductor diode I-V graph

Answer 8

It is a characteristic asymmetrical curve. Forward bias is a exponential curve which begin shortly after the threshold voltage. Reverse bias is a horizontal line from the origin followed by a near vertical line.

Question 9

Thermistor I-V graph

Answer 9

It is a reverse S-shaped curve that passes through the origin.
(line extend top right and bottom left to y infinity)

Question 10

Define resistivity

Answer 10

Resistivity is a measure of how strongly a material opposes electric current, It characterises the resistance of materials at a fixed temperature regardless of the materials’ dimensions.

Question 11

graph of terminal potential against I

Answer 11

I = 0 , V = emf
straight line graph with negative gradient