# A Torch and How it Works

In this worksheet, students will investigate the workings of a torch.

Key stage:  KS 2

Curriculum topic:   Electricity

Curriculum subtopic:   Variations in Functions of Components

Difficulty level:

### QUESTION 1 of 10

This worksheet tests your knowledge of how a torch works.

A battery-operated torch is an example of a simple circuit.

Most torches use metal strips within the circuit, instead of wires.

Look at this diagram of Leon's torch.

How many cells are there in the torch?

1 cell

2 cells

3 cells

Look at this diagram of Leon's torch.

As drawn, is the switch on or off?

on

off

Why do you think there is a metal spring in the torch?

To make it easier to remove the cells from the torch.

To keep the cells close to each other so they make a good contact.

To stop the cells from bouncing around in the torch and making noise.

Some torches have to have a case made of metal, or they do not work.

Why do you think this is?

The case protects the torch better than plastic.

The metal case helps the torch to work underwater.

The case acts as one of the wires in the circuit.

Each cell in Leon's torch can deliver 1.5 volts.

What voltage does the bulb require to glow normally?

zero volts

1.5 volts

3 volts

4.5 volts

In fact, when Leon pushes the switch to turn the torch on, he finds the torch won't work.

What do you think might be the problem?  Tick any of the following reasons that you think might be causing the torch not to work.

batteries are in the wrong way round

batteries have run down

bulb has 'blown'

wrong voltage bulb

batteries are the wrong size

switch is jammed

wires inside are damaged

the spring is rusty

the glass torch is broken

Leon's fingers are wet

Leon takes the bulb out of the torch and he tries it in this circuit:

When he closes the switch, the bulb doesn't come on.  Tick TWO reasons.

the circuit is not complete

the blub has blown

the wires are the wrong way round

the cell is the wrong way round

Once Leon has made sure the circuit works, he tries out the bulb from the torch and finds it's blown.

He finds another one that has 0.75V marked on the bulb, but it fits his torch.

Predict what you think will happen when he turns on the torch.

the bulb will work fine

the bulb will be a lot brighter than before

the bulb will 'blow'

Leon goes and rummages in his parents' electrical box of bits and pieces and he finds another bulb that fits his torch.

He puts it in but when he pushes the switch, he finds that the bulb his very dim.  Sigh!

What might be the problem?  Tick any reasons you think might be causing the dim bulb.

the voltage on the bulb is higher than 3V

the batteries are nearly flat

the switch has broken

he's forgotten to put the reflector in

he's left one of the cells out

Leon tries some new batteries and ... "hey presto!" - his torch works fine.  He's very happy.

He goes into his little brother, Tyler's, bedroom. It's quite dark in the bedroom.  Leon puts the torch in his mouth and turns it on.

Tyler shrieks, "What's that?  It's all red."

What do you think might be the reason that it looked red when Leon popped the torch in his mouth and turned it on?

Leon had cut his mouth with the torch

he had put a red bulb in it by mistake

the light showed the blood vessels inside his cheek

Tyler saw a reflection of Leon's Liverpool football shirt

• Question 1

Look at this diagram of Leon's torch.

How many cells are there in the torch?

2 cells
EDDIE SAYS
There are two C-sized cells shown in the diagram.
• Question 2

Look at this diagram of Leon's torch.

As drawn, is the switch on or off?

off
EDDIE SAYS
The switch is not touching the copper strips together. The copper strips act as wires in the torch. So, the switch is OFF.
• Question 3

Why do you think there is a metal spring in the torch?

To keep the cells close to each other so they make a good contact.
EDDIE SAYS
The cells are heavy and can easily come away from the back of the bulb. The spring keeps the cells touching each other by pushing them together and also against the contact of the bulb.
• Question 4

Some torches have to have a case made of metal, or they do not work.

Why do you think this is?

The case acts as one of the wires in the circuit.
EDDIE SAYS
In metal-cased torches, the case is used as one of the wires. Electricity cannot travel through plastic.
• Question 5

Each cell in Leon's torch can deliver 1.5 volts.

What voltage does the bulb require to glow normally?

3 volts
EDDIE SAYS
Each cell supplies 1.5V so the bulb receives a total of 3V and will glow normally. If less voltage is supplied the bulb will be dimmer or it might not light at all. If too much voltage is supplied then the bulb could break.
• Question 6

In fact, when Leon pushes the switch to turn the torch on, he finds the torch won't work.

What do you think might be the problem?  Tick any of the following reasons that you think might be causing the torch not to work.

batteries are in the wrong way round
batteries have run down
bulb has 'blown'
wrong voltage bulb
wires inside are damaged
the spring is rusty
EDDIE SAYS
There are loads of reasons! A rusty spring won't form an electrical contact (rust is an insulator) and most of the others should make sense to you. It won't stop the torch working if the glass is broken or his fingers are wet. The switch can't be jammed as he's pushed it OK and the batteries cannot be the wrong size as that would be immediately obvious.
• Question 7

Leon takes the bulb out of the torch and he tries it in this circuit:

When he closes the switch, the bulb doesn't come on.  Tick TWO reasons.

the circuit is not complete
the blub has blown
EDDIE SAYS
So, if there's a gap in the circuit or the bulb has blown, it won't light up. In fact, if the little filament wire inside the bulb breaks (that's when the bulb 'blows'), that creates a gap in the circuit anyway. By the way, wires cannot be the wrong way round and there's only one cell and that will happily push current either way, so the circuit will work.
• Question 8

Once Leon has made sure the circuit works, he tries out the bulb from the torch and finds it's blown.

He finds another one that has 0.75V marked on the bulb, but it fits his torch.

Predict what you think will happen when he turns on the torch.

the bulb will 'blow'
EDDIE SAYS
The cells in the torch are pushing out 3V. The bulb is marked at just a quarter of this voltage, so it won't last very long! It might just glow very brightly for a moment before it blows, but in all likelihood, it'll just go "phut" straight away!
• Question 9

Leon goes and rummages in his parents' electrical box of bits and pieces and he finds another bulb that fits his torch.

He puts it in but when he pushes the switch, he finds that the bulb his very dim.  Sigh!

What might be the problem?  Tick any reasons you think might be causing the dim bulb.

the voltage on the bulb is higher than 3V
the batteries are nearly flat
he's forgotten to put the reflector in
EDDIE SAYS
Leon's having a bad time with this torch! It's quite probable that the voltage on the bulb is higher than the 3V of the cells, but then again the cells might be on their way out and if he's forgotten to put the reflector back in, the light won't be focussed.
• Question 10

Leon tries some new batteries and ... "hey presto!" - his torch works fine.  He's very happy.

He goes into his little brother, Tyler's, bedroom. It's quite dark in the bedroom.  Leon puts the torch in his mouth and turns it on.

Tyler shrieks, "What's that?  It's all red."

What do you think might be the reason that it looked red when Leon popped the torch in his mouth and turned it on?

the light showed the blood vessels inside his cheek
EDDIE SAYS
Big brothers, honestly! In fact, you can try this yourself. In a darkened room and with a powerful torch, if you put it into your mouth, and look in the mirror, or if you shine it through the webbing between your thumb and index finger, the red colour you see is the light shining through your blood vessels. Weird, but true!
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