Bright Lights

What happens when there is more than one bulb in a circuit?

This is a special online experiment which will try to answer this question. But before you can start, you need to know a little about circuits and light bulbs. Click the play arrow to see a short animation which tells you what you need to know.

You're going to carry out an investigation to find out what happens when there is more than one bulb in a circuit. But instead of using a laboratory, you'll be doing your experiment in cyberspace. If you do the experiment well, you'll score enough points to see a photo gallery.

Which circuit will have the brightest bulb or bulbs?

Click 'Select' to choose one picture

  • A circuit with one battery and one bulb

  • A circuit with one battery and two bulbs

  • A circuit with one battery and three bulbs

On this screen you will plan how to make a fair test to find out what happens when there is more than one bulb in a circuit. To help you think about this, click 'True' or 'False' for each statement.

  • For a fair test the only thing you should change is the number of bulbs.

  • You should use the same battery to test each set of bulbs.

  • The bulbs do not have to be the same type in each circuit.

Here are three ways the test could be set up. Look at the pictures carefully then click 'Select' on the one which you think is closest to a fair test.

  • Make the three circuits and leave them on then see how long the battery lasts.

  • Make the circuit with one bulb, test it then add a second bulb, test it then add a third bulb and test it.

  • Make the three circuits separately and compare how bright the bulbs are.

You are going to make a circuit with one battery and one bulb to start with, then add a second bulb, then add a third bulb. To help you think about this, answer each question by clicking 'True' or 'False':

  • The same type of wire should be used in each circuit.

  • You should leave each circuit on for a long time to test.

  • The length of the wires does not matter.

In good science investigations, measurements are taken to find out what is happening. How can you measure the brightness of the bulbs in this experiment?

Click 'Select' to pick one answer.

  • Look at the bulbs and see which ones are brightest.

  • Measure how far away you can see the bulbs in each circuit.

  • Count how many pieces of white paper you can see the bulbs through.

You are going to use white paper to measure but which type is best?

Click 'Select' to pick one answer.

  • Thin white paper.

  • Medium white paper.

  • Thick white paper.

You’re ready to start. This is what you must do next in order to collect evidence to say what happens when there is more than one bulb in a circuit:

  • Test the circuit with one bulb first.
    Click on 'Connect' to attach the wire to the battery and complete the circuit.

  • The bulb is now on. You need to find out how bright it is by screening it with sheets of paper.
    Click 'Add paper' to form a screen with the first sheet.

  • The light is still showing.
    Keep clicking 'Add paper' until you can’t see it at all.

It is very important to write down results during an experiment. You’ll have to type them into a chart or table of some sort. Click magnify to view each table, then press 'Select' to choose the one which you think is best.

You’ve done top work so far. The experiment is running now. You need to record how many pieces of paper it took to block the light in the circuit with one bulb. Click the right place in the table and type the answer. Then click on 'OK'.

Table

C
Number of bulbs Number of pieces of paper need to block the light
1
2  
3  
  • Now test the circuit with two bulbs. To do this click 'Test circuit'.

  • The circuit with two bulbs is now working. Next you need to click 'Add paper' to form a screen and measure how bright the bulbs are.

  • Very interesting! Next you need to record the results in the table again. To do this, click the table in the right place and add the number of pieces of paper that blocked the light.

  • Now test the circuit with three bulbs. To do this click 'Test circuit'.

  • The circuit with three bulbs is now working. Next you need to click 'Add paper' to form a screen and measure how bright the bulbs are.

  • Very interesting! Next you need to record the results in the table again. To do this, click the table in the right place and add the number of pieces of paper that blocked the light.

Table

C
Number of bulbs Number of pieces of paper need to block the light
1 4
2 2
3 1

The experiment results are now all in, but what have you found out? You can display the results in a graph to see the pattern of outcomes. Click magnify to see the graphs below in more detail. Then click 'Select' to choose the one which is labelled correctly:

The graph needs a title plus numbers and labels on the axes. Click magnify to see the graphs below and then click 'Select' to choose the graph which shows the results of your experiment correctly:

You’re nearly finished! You just need to decide what the results tell us about the brightness of different numbers of bulbs in a circuit – this is called making a conclusion. First, click magnify to have a look at the results table and the graph.

When you have looked at the results and graph, click 'True' or 'False' for each question below:

  • The more bulbs in this circuit, the brighter they are.

  • The single bulb was brighter than the two bulbs together.

  • The three bulbs in a circuit with one battery were very dim.

Click on the statement that the results of your experiment support

  • The more bulbs in a circuit with one battery, the less bright they will be.

  • The three bulbs in a circuit are always dim.

At the start of the experiment you predicted that the bulbs in the one bulb circuit would glow the brightestthat the bulbs in the two bulb circuit would glow the brightestthat the bulbs in the three bulb circuit would glow the brightest. Do you still think this is the case?

Well done: you’ve carried out an experiment and found evidence that in some circuits, adding bulbs makes them dimmer. Here are three final questions to think about - maybe you can discuss them with your friends or teacher. See what Kate and Dev have to say about them.

  • Was this a fair test?

  • Does it matter what kind of battery or bulbs you use?

  • Why are three bulbs dimmer in this kind of circuit?

The test was fair because the same circuit was used with the same battery each time.
Yes it does matter. There are different kinds of batteries and some are too powerful for the small bulbs you used here.
The two-bulb and three-bulb circuits had dimmer bulbs because they had to share the battery’s electricity. This was because you used what is called a series circuit, with all the bulbs in a line.
The circuit with the three bulbs in was a little longer than the other two because more wires were needed but this would not really affect the result.
The important thing was that you used the same bulbs and the same battery in each part of the test.
You could make a parallel circuit with one battery and three bulbs where all the bulbs glow as brightly as a single bulb would because they are wired directly to the battery.

Congratulations, you’ve done it!

Bad luck, you didn't make it!

You scored enough to see the real life light bulbs gallery.
Click 'Next' to go to the gallery, or 'Try again' to have another go.

You needed to score 18 out of 25 to see the real life light bulbs gallery.
Click 'Try again' to have another go.

There are circuits with light bulbs everywhere. Most of them are wired so the bulbs don’t get dim if there is more than one! Here are some examples of the different ways they are used.

Question

The experiment is under way. The circuit with one bulb needed four pieces of paper to block out the light.

Do you need to record this information?

Click 'Yes' or 'No':

Table of Results

You score: Two points