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# Investigate the resistance if 12 volt bulb when the current changes.

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Introduction

Aim: to investigate theresistance if 12 volt bulb when the current changes.

Prediction: I predict that as the current increases the temperature of the lamp will also increase; therefore the resistance will also increase. I know this because I have read it in the AQA syllabus.

###### Plan

Safety: I need to ensure the safety of myself and others by making sure that the experiment is conducted accurately and safely.

• Apparatus should be placed in a safe place and put away safely.
• Electrical plugs should be switched off after use.
• The area should be kept dry and taps should be switched off.

Variables: I will only be changing the current by moving the variable resistor.

I will repeat the experiment twice so that I can be sure of my readings and see if anything has changed or gone wrong.

Middle  1. I will do a preliminary test to find the range of current in amps. I will do this by moving the variable resistor to its lowest and highest points and noting down the amps. In this case the lowest point is 0.5 and the highest is 1.6 amps.
1. I will start with 0.5 amps, working systematically, I will note down the voltage every 0.1 amps. I will do this until I reach the highest point which is 1. 6 amps. I will then repeat this to see if my results have changed or are the same.

Fair test: To make this investigation a fair test I will use the same equipment and the same method every time I repeat the experiment so that nothing will change. I will also wait until the lamp cools down so that it is at the same temperature that it was when I first used it.

##### Obtaining evidence

A table of my results:

 Current (amps) Voltage (volts) Voltage (volts) Experiment 1 Experiment 2 0.5 1 1 0.6 1.5 1.5 0.7 2 2 0.8 3 3 0.9 4 4 1 5 4.5 1.1 5.5 6 1.2 7 7 1.3 8 8 1.4 9 9 1.5 10 10 1.6 11 11

Conclusion

To  make this experiment  more accurate I could have used electronic equipment which would accurately measure the volts and amps so that there would be no human errors.  To extend this investigation I could have used different types of bulbs with a different size of maximum voltage. I could have taken more readings, perhaps repeated the experiment a few more times and used a wider range of current.

Using my graph I can see that there are two anomalies; the other results are all close to the line of best fit. These two anomalies are near the higher end of the graph and are not near the line of best fit. The reason for these odd results may be because there was human error involved or factors such as the temperature of the lamp. With the time that I was given I think that enough results were taken to support the conclusion.

To help me with my investigation I used the following secondary resources:

• AQA syllabus
• Modular science for AQA

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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