12.4 Components and their characteristics

Question 1

What is a cell

Answer 1

A source of electrical energy

Question 2

What is a battery

Answer 2

A combination of cells

Question 3

What is the symbol for an indicator the same as

Answer 3

For a light source including filament lamp but NOT an LED

Question 4

What is a diode

Answer 4

Allows current in one direction ONLY

LED emits light when it conducts

Question 5

What is the direction in which a diode conducts referred to

Answer 5

As its forward direction

Question 6

What is the direction opposite to which a diode conducts referred to

Answer 6

As its reverse direction

Question 7

What are diodes used for

Answer 7

The protection of dc circuits for example, in case the voltage supply is connected the wrong way around

Question 8

What is a resistor

Answer 8

A component designed to have a certain resistance

Question 9

How does the resistance of a thermistor change as temperature increases

Answer 9

The resistance decreases if it is an intrinsic semiconductor such as silicon

Question 10

How does the resistance of a light-dependent resistor (LDR) change as light intensity increases

Answer 10

The resistance decreases

Question 11

What does LDR stand for

Answer 11

Light-dependent resistor

Question 12

What does LED stand for

Answer 12

Light-emitting diode

Question 13

How to measure the variation of current with pd for a component

Answer 13

Use either a potential divider to vary the pd from zero or a variable resistor to vary the current to a minimum

Question 14

What is the advantage of using a potential divider than a variable resistor

Answer 14

The current through the component and the pd across it can be reduced to zero which isn’t possible when using a variable resistor

Question 15

What is the shape of the IV graph of a wire

Answer 15

A straight line through the origin

Question 16

What is the shape of the IV graph of a filament bulb

Answer 16

Curve with a decreasing gradient because its resistance increases as it becomes hotter

Question 17

What is the shape of the IV graph of a thermistor

Answer 17

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.

Question 18

How does the resistance of a metal change when temperature increases

Answer 18

The resistance increases

Question 19

Why does the resistance of a metal increase as temperature increases

Answer 19

This is because the positive ions in the conductor vibrate more when its temperature is increased. The charge carriers therefore cannot pass through the metal as easily when a pd is applied across the conductor.

Question 20

Why is a metal said to have a positive temperature coefficient

Answer 20

Because its resistance increases with increase of temperature

Question 21

How does the resistance of an intrinsic semiconductor change with an increase in temperature

Answer 21

The resistance decreases as the number of harge carriers (conduction electrons) increases when the temperature is increased. Therefore, a thermistor made from an intrinsic semiconductor has a negative temperature coefficient