Ohm’s Law Lab (60 points)
Warning: Do not touch any live wires or leads. Show your circuit to your teacher before
connecting the power supply.
Purpose: Investigate relationship between current, voltage and resistance.
Materials: Voltmeter, Ammeter, 2 resistors (100  and 250 ), power supply, switch, wires, board
:
Procedure: Set up equipment as shown above. Use 100 and 250  resistances. Make sure you show
your circuit to the teacher for approval before connecting the power supply. Increase carefully the
voltage to read 2 V to 6 V. Use a switch in the circuit and close the switch only for as long as you
need to note the ammeter and voltmeter readings.
Plot a graph between current ‘I’ (A) on the x-axis and V (V) on the y-axis. You will get two straight
lines, whose two slopes will be equal to the actual resistances.
Put away everything neatly after you are done. (5 points)
Data: (20 points)
Theoretical
Resistance ‘R’ ()
Voltage (V)
100
2
100
3
100
4
100
5
100
6
250
2
250
3
250
4
250
5
250
6
1000 mA = 1 A
Current ‘I’ (mA)
Measured Resistance
()
V/I
Find the slopes of the two lines plotted in the graph (25 points)
V (V)
I (mA)
Conclusion: (10 points)
1. How does the resistance of a wire depend (a) on its length? (b )On its area of cross section?
2. How does temperature affect resistance of a material?
3. (a) Are electrons free to move in an insulator? (b) How about metals? (c) What metals are the
best conductors
4. The power supplies can carry up to several amperes of current. Is that dangerous?
5.
(a) What are super conductors? (b) What are semi-conductors? Give examples of both.