# Changing Wires Changing Circuits

In this worksheet, students will be helped to consider the effect of changing the length and thickness of wire in a circuit in terms of how much current flows and how components are affected.

Key stage:  KS 2

Curriculum topic:   Electricity

Curriculum subtopic:   Variations in Functions of Components

Difficulty level:

### QUESTION 1 of 10

Mrs. Bates's science class were working on electric circuits.

First of all, they were investigating how the length of a piece of wire affected different components in a circuit. They started by setting up a simple circuit using a cell and a bulb connected by two clips into which lengths of wire could be inserted to complete the circuit:

Mrs. Bates divided her class into ten groups and gave each group three different lengths of wire for them to test: 10cm, 20cm and 30cm.

In order to ensure that this was a 'fair test' investigation the groups would have to keep certain things the same. Tick all the ones you agree with from this list.

same length of wire

same thickness of wire

same type of wire

same type of bulb

same type of cell

same condition and wear of cell

What would the groups be comparing to see whether the length of wire affected the circuit?

speed of electric current

brightness of bulb

speed of motor

Which length of wire would you expect to have the greatest impact on how well the circuit works?

10 cm

20 cm

30 cm

What do you think is the most important reason for Mrs. Bates dividing her class into ten groups for this investigation?

so that everyone had a go

she had enough components for ten groups

to get enough meaningful results

Next Mrs. Bates introduced her class to a new piece of electrical equipment called an AMMETER.

She explained that ammeters measure the electrical current in a circuit - how fast it is travelling - and the higher the reading the higher the current.

She also explained that scientists measure the current in AMPS (shortened to 'A').

The symbol used in circuit diagrams for an ammeter is:

Which of these readings represents the highest current?

0.01A

0.05A

0.2A

Mrs. Bates explained to her class that they would be using the ammeter to investigate how much current flowed around their circuit as they changed the thickness of the wire.

She asked them to construct this circuit:

The students would be adding different thicknesses of wire between the clips, checking that the bulb came on and noting the reading of the current on the ammeter.

Which things do you think the students had to keep the same in this investigation to make sure it was a 'fair test'?

same length of wire

same thickness of wire

same type of wire

same type of bulb

same type of cell

same type of ammeter

same groups as before

Mrs. Bates had five ammeters and so divided her class into five groups to test the thicknesses of wire: thick, medium, thin.

Here are their results:

 GROUP Thick wire/A Medium wire/A Thin wire/A 1 2 3 4 5 0.2 0.2 0.2 2 0.2 0.1 0.1 0.1 1 0.1 0.06 0.05 0.05 5 0.03

One group seems to have made a mistake - which group?

1

2

3

4

5

What mistake do you think this group made?

they only wrote the significant figure from their reading

they could not read their ammeter display

they didn't connect their ammeter properly

Mrs. Bates then asked her class to draw a bar graph of the class's results, ignoring the ones that were wrong:

Looking at these results what do you conclude about the effect of the thickness of the wire in the current around a circuit?

the thicker the wire the greater the current

the thicker the wire the smaller the current

the thinner the wire the greater the current

What do you think would have happened to the brightness of the bulb as the wire thickness was changed from thick to medium to thin?

it became dimmer

it became brighter

its brightness stayed the same

• Question 1

In order to ensure that this was a 'fair test' investigation the groups would have to keep certain things the same. Tick all the ones you agree with from this list.

same thickness of wire
same type of wire
same type of bulb
same type of cell
same condition and wear of cell
EDDIE SAYS
In fact most things have to be as similar as possible! For example if one group's cell is old and nearly dead that will affect the results; if one group use copper wire and another group use constantan (resistance) wire, the results will be different. Obviously the length of wire is not right as that is what the class are investigating!
• Question 2

What would the groups be comparing to see whether the length of wire affected the circuit?

brightness of bulb
EDDIE SAYS
The only component in their circuit that can be used to measure whether the length of wire has had an effect is the bulb. They will need to decide on a 'measure' of brightness.
• Question 3

Which length of wire would you expect to have the greatest impact on how well the circuit works?

30 cm
EDDIE SAYS
The longer the wire the more resistance it creates: basically it's harder for the cell to push the current around the circuit. So the 30 cm wire will give the dimmest bulb.
• Question 4

What do you think is the most important reason for Mrs. Bates dividing her class into ten groups for this investigation?

to get enough meaningful results
EDDIE SAYS
They're all sensible suggestions but scientifically-speaking it's important that any investigation is carried out many times to see if the results are the same. At school that's not possible so the best alternative is to have lots of groups doing the same experiment with the same kit and then there's lots of data to compare.
• Question 5

Next Mrs. Bates introduced her class to a new piece of electrical equipment called an AMMETER.

She explained that ammeters measure the electrical current in a circuit - how fast it is travelling - and the higher the reading the higher the current.

She also explained that scientists measure the current in AMPS (shortened to 'A').

The symbol used in circuit diagrams for an ammeter is:

Which of these readings represents the highest current?

0.2A
EDDIE SAYS
Standard numbers - the highest number there is 0.2, so that's the highest current: 0.2A.
• Question 6

Mrs. Bates explained to her class that they would be using the ammeter to investigate how much current flowed around their circuit as they changed the thickness of the wire.

She asked them to construct this circuit:

The students would be adding different thicknesses of wire between the clips, checking that the bulb came on and noting the reading of the current on the ammeter.

Which things do you think the students had to keep the same in this investigation to make sure it was a 'fair test'?

same length of wire
same type of wire
same type of bulb
same type of cell
EDDIE SAYS
As before it is important to try to keep everything as near the same as possible across the groups. To be honest the type of ammeter probably doesn't matter as they're all set up to read the current, whereas similar bulbs and cells is important as they will affect the current. The thickness of the wire is what's under investigation, so that shouldn't be kept the same.
• Question 7

Mrs. Bates had five ammeters and so divided her class into five groups to test the thicknesses of wire: thick, medium, thin.

Here are their results:

 GROUP Thick wire/A Medium wire/A Thin wire/A 1 2 3 4 5 0.2 0.2 0.2 2 0.2 0.1 0.1 0.1 1 0.1 0.06 0.05 0.05 5 0.03

One group seems to have made a mistake - which group?

4
EDDIE SAYS
Clearly it's group 4 - their results are totally different to all the other groups.
• Question 8

What mistake do you think this group made?

they only wrote the significant figure from their reading
EDDIE SAYS
It looks as though they've ignored the 0s and decimal point and just gone for the significant figure, if you compare their readings with the rest of the class. It's probably not an inability to read the ammeter display and Mrs. Bates will have checked they'd connected it properly before they took their readings.
• Question 9

Mrs. Bates then asked her class to draw a bar graph of the class's results, ignoring the ones that were wrong:

Looking at these results what do you conclude about the effect of the thickness of the wire in the current around a circuit?

the thicker the wire the greater the current
EDDIE SAYS
It's clear from the graph that as the wire gets thinner the reading decreases. In fact if you imagine that electric current is rather like water flowing along a pipe, making the wire thin is similar to having a section of thin piping - it's harder for the water to get through so everything slows down. That's why the current reading decreased.
• Question 10

What do you think would have happened to the brightness of the bulb as the wire thickness was changed from thick to medium to thin?

it became dimmer
EDDIE SAYS
As the wire became thinner the current decreased. That means that the bulb was receiving less current so it\'ll be dimmer.
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