Components and their characteristics

Question 1

To measure the variation of current with pd for a component use either:

Answer 1

• A potential divider to vary the pd from zero
• A variable resistor to vary the current to a minimum
• Then plot a current over pd graph

Question 2

The resistance of a metal increases with increase of temperature.

Answer 2

This is because the positive ions in the conductor vibrate more when it’s temperature is increased. The charge carriers therefore cannot pass through the metal as easily when a pd is applied across the conductor. A metal is said to have a positive temperature coefficient because it’s resistance increases with increase of temperature.

Question 3

The resistance of an intrinsic semiconductor decreases with increase of temperature.

Answer 3

• This is because the number of charge carriers increases when the temperature is increased.
• A thermistor made from an intrinsic semiconductor therefore has a negative temperature coefficient.
• Its percentage change of resistance per kelvin change of temperature is much greater than for a metal.
• For this reason, thermistors are often used as a temperature sensitive components in a temperature sensor.

Question 4

To investigate the characteristics of a diode:

Answer 4

• One set of measurements is made with the diode in its forward direction and another set in its reverse direction.
• The current is very small when the diode is reverse biased and can only be measured using a milliammeter.

Question 5

Cell

Answer 5

A cell is a source of electrical energy. A battery is a combination of cells

Question 6

Indicator

Answer 6

The symbol for an indicator is the same as that for a light source except a LED.

Question 7

Diode

Answer 7

• A diode allows current in one direction only.
• An LED emits light when it conducts.
• The direction in which the diode conducts is referred to as its forward direction.
• The opposite direction is referred to as the reverse direction.
• Diodes can be used to protect DC circuits if the voltage supply is connected the wrong way.

Question 8

Resistor

Answer 8

A resistor is a component designed to have a certain resistance.

Question 9

Thermistor

Answer 9

The resistance of a thermistor decreases with increasing temperature, if the thermistor is an intrinsic semiconductor such as silicon.

Question 10

Light Depenedebt Resistor

Answer 10

The resistance of an LDR decreases with increasing light intensity.

Question 11

Wire Graph

Answer 11

A wire gives a straight line through the origin. This means that any point on the line, the value of V/I is the same. The resistance of the wire does not change when the current changes. The gradient is equal to the reciprocal of resistance.

Question 12

Filiament bulb graph

Answer 12

A filiament bulb gives a curve with decreasing gradient because its resistance increases as it becomes hotter.

Question 13

Thermistor graph

Answer 13

A Thermistor at constant temperature gives a straight line. The higher the temperature, the greater the gradient of the line, as the resistance falls with increase of temperature. The same result is obtained for a light-dependent resistor in respect of light intensity.

Question 14

Diode graph

Answer 14

• In the forward-biased direction there is a high resistance up to about 0.6 V (small I rising gradually). At 0.6 V resistance decreases and there is a sharp increase in current.
• In the reverse-biased direction there is a high resistance and zero current.