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# design of a variable resistor

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Introduction

International School of Phnom Penh                                                5199

Candidate name: HOZUMI Haruka                                          Page  of

Candidate Number                                                             Science

Design of a Variable Resistor

Aim: Our aim is to find the most suitable length and thickness of wire for the variable resistor with a broken wire. We will determine the difference in resistance between three copper wires with different diameter, and three wires with different lengths (10cm, 15 cm 20 cm).

We chose these lengths. We thought that three different lengths would be enough to

Hypothesis:

Diameter: We think that larger the diameter of copper wire, it will have more resistance because copper wire generally has higher resistance. Since it is largest, it will have more resistance.

Length: We think that the longer the wire, the resistance will be higher because the electricity has to travel longer distance.

We think that

We chose these diameters because

Apparatus:

• Copper wires (3 diameter size, all 10cm)
• Copper wires (3 different lengths – 10cm, 15cm, 20cm)
• Power cell
• Ammeter
• Variable resistor
• Volt meter
• Wires (to connect)
• Scissor
• Ruler
• Calculator
• Crocodile clips

Independent variables:

• Diameter of wires – for testing diameter
• Lengths of wires – for testing lengths

Controlled Variables:

• Length of the wires (for testing diameter) – we will make the wires as straight as we can, and use a ruler to cut them in same size (length). The lengths have to be same because if it is different, the test would not be fair.
• Diameter of the wires (for testing lengths) – we will use the same type (size). The diameters have to be same because if it is different, the test would not be fair.
• All the wires should be straight so that the electricity can travel easy.
• Voltage – we will keep the power cell to 3 V to make the experiments fair.
• Use the same apparatus (variable resistor, ammeter, volt meter) to make the experiments fair.

Dependent variables:

• Resistance - We will measure by using the volt meter and ammeter. We will use the Ohm’s Law (Voltage = Current * Resistance)with a calculator to find the resistance.

Middle

0.046

Testing a copper wire with diameter of       3rd experiment

Diameter (   mm)

Ammeter (amp)

Voltage (V)

Resistance (Ohm)

4.7

0.28

0.05957447

4.75

0.28

0.05894737

4.8

0.3

0.0625

Average resistance of the 3 Wires with Different Thickness (Diameter)

 Diameter (mm) Resistance (Ohm) 0.06174412 0.059712123 0.05657483

Difference

mm – mm =0.002031997

mm – mm =0.003137293

Average difference = 0.002584645

Lengths

Testing Copper wire with length of               1st experiment

Lengths (cm)

Ammeter (amp)

Voltage (V)

Resistance (Ohm)

10 cm

4.6

0.3

0.06521739

15 cm

4.65

0.32

0.0688172

20 cm

4.55

0.32

0.07032967

Testing Copper wire with length of                 2nd experiment

Lengths (cm)

Ammeter (amp)

Voltage (V)

Resistance (Ohm)

10 cm

4.7

0.3

0.06382979

15 cm

4.7

0.3

0.06382979

20 cm

4.65

0.32

0.0688172

Testing Copper wire with length of         3rd

Conclusion

To improve our methods, we could have used longer wires (for the diameter experiment) to see bigger differences. For the lengths experiment, we could have used three different lengths with more difference. (e.g. 15, 30, 45), also to see larger differences. We also can use ammeter and volt meter with bigger space between each numbers.I think the first suggested improvement, which is to change the lengths of the wires would make more differences in resistances between the three wires. The second suggested improvement, which is to use bigger ammeter/volt meter (ones with bigger space between each numbers) will make the results clearer. It will give the accurate results since it is easier to see.To follow up this investigation, I can now do an experiment with different types of wires (e.g. copper, lead, nickel, etc) to test which type has the highest resistance and which has the lowest.This will be useful. Variable resistors are important since it is used in many places such as in science lab and in household electrical equipments. If we know the resistance of each types of wires, we will know how long or big (thickness) of the wire is suitable for the replacement of the variable resistors. If we know the resistance of different types of wires, we can also find the cost-effective way to make variable resistors.

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