Required Practical 16 - I-V Characteristics

Question 1

How does the length of a piece of wire affect its resistance?

Answer 1

First, the total length of the wires will affect the amount of resistance. The longer the wire, the more resistance that there will be

In the same manner, the wider the wire, the less resistance that there will be to the flow of electric charge.

Question 2

What is the appropriate hypothesis for this required practical?

Answer 2

The resistance of a piece of wire should increase with length because the moving electrons that make up current have to travel through more wire

and they’ll collide with more atoms while travelling

so will lose more energy in the process of doing so

Question 3

What is the equipment needed for this required practical?

Answer 3

• Meter ruler
• Resistance wire attached to metre ruler with resistance tape
• Crocodile clips to clip circuit to wire
• Ammeter in series with a switch, resistor and battery
• Voltmeter in parallel on the opposite side

Question 4

Why are crocodile clips used in this practical?

Answer 4

Changing the position of one crocodile clip can change the length of wire connected as part of the complete electric circuit, hence changing the resistance to be measured

Question 5

Which kind of wire is best to use?

Answer 5

Best to use a thin piece of resistance wire (e.g. 0.1mm - diameter Constantan or similar)

Question 6

What is the purpose of a fixed resistor?

Answer 6

It limits the maximum current through the wire to safe levels
E.g. below 1 amp

Question 7

What will happen if the current gets too high, what is the solution for this?

Answer 7

The wire starts to get quite hot

This poses a safety risk to experimenter

Opening the switch between readings to stop the flow of current through the wire further reduces the risk of burning

Question 8

Give the method for this required practical

Answer 8

1. Connect 20cm of wire to the below circuit using crocodile clips
2. Measure and record the p.d. (potential difference) across the wire (V) and the current through it (I)
3. Calculate the resistance of the wire (using V = IR, rearrange to give R = V/I)
4. Repeat steps 2 - 3 for a number of different lengths of wire (30, 40, 50, 60, 70, 80, 90 cm)