RPA

Question 1

RPA 5 - Variables

Answer 1

Independent variable = Length, L, of the wire (m)
Dependent variable = The current, I, through the wire (A)
Control variables:
Voltage through the wire
The material the wire is made from

Question 2

RPA 5 - Aims of the Experiment

Question 3

RPA 5 - Equipment List

Answer 3

Question 4

RPA 5 - Resolution of measuring equipment:

Answer 4

Metre ruler = 1 mm
Micrometer screw gauge = 0.01 mm
Voltmeter = 0.1 V
Ammeter = 0.01 A

Question 5

RPA 5 - Method of measuring wire diameter

Answer 5

Measure the diameter of the constantan wire using a micrometer. The measurement should be taken between 5-10 times randomly along the wire.
Calculate the mean diameter from these values

Question 6

RPA 5 - Method of measuring wire diameter

Answer 6

• Set up the equipment so the wire is taped or clamped to the ruler with one end of the circuit attached to the wire where the ruler reads 0.
• Attach the flying lead to the test wire at 0.25 m
• Set the power supply at a voltage of 6.0 V.
• Read and record the current from the ammeter, then switch off the current immediately after the reading
• This is to prevent the wire from heating up and changing the resistivity
• Vary the distance between the fixed end of the wire and the flying lead in 0.25 m intervals (0.25 m, 0.50 m, 0.75 etc.) until the full length of the 2.0 m wire.
• Record the current for each length at least 3 times and calculate an average current, I
• For each length, calculate the average resistance of the length of the wire using the equation R = V / I

Question 7

RPA 5 - results analysis

Answer 7

Question 8

RPA 5 - Evaluating the Experiment - systematic errors

Answer 8

The end of the wire that is attached to the circuit (not the flying lead) must start at 0 on the ruler
Otherwise, this could cause a zero error in your measurements of the length

Question 9

RPA 5 - Evaluating the Experiment - random errors

Answer 9

• Only allow small currents to flow through the wire
• The resistivity of a material depends on its temperature. The current flowing through the wire will cause its temperature to increase and affect its resistance and resistivity. Therefore the temperature is kept constant and low by small currents
• The current should be switched off between readings so its temperature doesn’t change its resistance
• Make at least 5-10 measurements of the diameter of the wire with the micrometer screw gauge and calculate an average diameter to reduce random errors in the reading

Question 10

RPA 5 - Evaluating the Experiment - Safety Considerations

Answer 10

• When there is a high current, and a thin wire, the wire will become very hot.
• Make sure never to touch the wire directly when the circuit is switched on
• Switch off the power supply right away if you smell burning
• Make sure there are no liquids close to the equipment, as this could damage the electrical equipment