Current of Electricity and DC Circuits

Question 1

Electric current

Answer 1

The rate of flow of charge.

Question 2

Potential difference between two points*

Answer 2

The p.d. across two points in a circuit is the work done per UNIT CHARGE when electrical energy is transferred to non-electrical energy when the charge passes from one point to the other.

Question 3

Electromotive force of a source*

Answer 3

The e.m.f. of a source is the work done per unit charge when non-electrical energy is transferred into electrical energy when the charge is moved round a complete circuit.

Question 4

Resistance

Answer 4

The resistance of a component is defined as the RATIO of the potential difference V across the component to the current I passing through it.

Question 5

Ohmic resistor

Answer 5

As potential difference V increases, current I increases proportionately. Thus resistance R remains constant.

Question 6

Filament lamp

Answer 6

As potential difference V increases, current I increases initially. Further increase of V causes a less than proportionate increase in I, so R increases with increasing V.

This is because for a metal, as temperature increases, n will not increase significantly but the amplitude of atomic vibration increases. So R increases

Question 7

Semiconductor diode

Answer 7

As V increases, temperature of the semiconductor increases. Electrons in semiconductor are more likely to have sufficient energy to escape from a particular atom if the temperature is higher, which increases n significantly. At the same time, there is also an increase in rate of interaction of electrons with the vibrating atoms. However, as the increase in n predominates over the rate of interactions of electrons with the lattice, the overall effect is that R decreases.

In the reverse-biased region, there is no current flow through the diode until the breakdown voltage.

Question 8

Negative Temperature Coefficient (NTC) Thermistor

Answer 8

An NEGATIVE TC thermistor’s resistance falls as the temperature rises. As the temperature increases, the number of charge carriers per unit volume in the material increases, reducing its resistance. As such, its I-V characteristic is the same as that for a semiconductor diode for positive values of V and I.