Physics - Electric circuits

Question 1

Draw the symbol for a cell

(which is the same as a battery in a circuit)

Answer 1

Question 2

Draw the symbol for a switch

draw it OPEN, not CLOSED!

Answer 2

Question 3

Draw the symbol for a LAMP

Answer 3

Question 4

Draw the symbol for a VOLTMETER

Answer 4

Question 5

Draw the symbol for an AMMETER

Answer 5

Question 6

Draw the symbol for a RESISTOR

Answer 6

Question 7

Draw the symbol for a VARIABLE RESISTOR

Answer 7

Question 8

Draw the symbol for a FUSE

Answer 8

Question 9

Draw the symbol for a LED

(Light Emitting Diode)

Answer 9

Question 10

Draw the symbol for a THERMISTOR

and what does a thermistor do?

Answer 10

A thermistor is a resistor which changes it’s resistance depending upon the temperature

Question 11

Draw the symbol for a LDR

(Light Dependent Resistor)

and what does it do?

Answer 11

An LDR is a resistor which changes it’s resistance depending upon how much light is shining on it.

Question 12

Draw the symbol for a DIODE

Answer 12

Question 13

Describe electrical CURRENT

Answer 13

The symbol ‘I’ is used for electrical current.

Current is the flow of electrons around an electrical circuit.

It is measured in amperes, symbol ‘A’

It is measured by an ammeter, which needs to be in series

Question 14

What is VOLTAGE

Answer 14

Voltage is a measure of how much electrical energy a certain amount of electrons can transfer as they flow around a circuit.

The higher the voltage, the more electrical energy is supplied to the circuit.

Voltage is measured in Volts, symbol ‘V’

Measured by a voltmeter, connected in PARALLEL

Question 15

Two bulbs - B1 and B2 - are connected together along with a battery (cell).

Describe how they are fastened together -

are they in series or in parallel?

And what happens if bulb B1 breaks?

Answer 15

B1 and B2 are connected in series

If bulb B1 breaks then bulb B2 will not work

Question 16

Describe how bulbs B1, B2 and B3 are connected.

What happens to bulb B2 and B3 if bulb B1 breaks?

Answer 16

B1 and B2 are in series

B3 is in parallel to B1 & B2

If B1 breaks then B2 will not work but B3 will still work

Question 17

What happens to

voltage (volts) and current (amps)

in a circuit where two bulbs are in series?

Answer 17

The voltage is split across both bulbs. So, in the picture, if the voltage from the battery is 6V, and the voltmeter V₁ shows 3V, then the voltmeter V₂ will also show 3V (3V+3V=6V)

The current through both bulbs in series is the same

Question 18

What happens to

voltage (volts) and current (amps)

in a circuit where two bulbs are in parallel?

Answer 18

The current is split across B1 and B2

The voltage is the same through both bulbs

Question 19

Give some uses of a variable resistor

Answer 19

A variable resistor (rheostat) is a resistor for which it is possible to alter/vary the resistance. This allows you to control the current in a circuit.

Examples:

1. DIfferent heat settings on a hairdryer
2. A dimmer switch on the lights in a room
3. The volume control on a radio

Question 20

Explain Ohms Law

Answer 20

It is the equation which links resistance, voltage and current.

…. so if you know two of the three, you can work out the third.

Question 21

Define

electrical power

Answer 21

This is the rate (per second) of energy transfer

It is measured in watts

There is an equation to calculate it

Power = voltage (volts) x current (amps)

Question 22

Give an example of how a light dependent resistor is used

Answer 22

The resistance changes according to the amount of light.

They can be used to automatically switch on street lights

Question 23

Give an example of how a thermistor is used

Answer 23

The resistance changes according to the temperature.

They can be used to set off fire alarms if the temperature in a room goes too high