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Ohm’s Law
SNC 1DW
Name: _________________
Purpose:
To determine the relationship between current, voltage and resistance in an electric
circuit.
Materials: ammeter
power supply
voltmeter
switch
resistor of known resistance
connecting wires
Procedure:
1. Build the circuit shown below.
º
º
A
A
V
2. Turn the dial on the power supply to zero (counter clockwise) and turn on the switch.
Watch the voltmeter and slowly turn the dial until the meter reads 1V.
3. Record the current at this voltage in the observation table on the next page.
TURN OFF THE POWER SUPPLY WHILE RECORDING YOUR VALUES! If the
resistor gets too hot, it will melt and not give you the correct results.
4. Turn the power supply back on and turn the dial until the voltmeter reads 2V. Again,
record the current at this voltage.
5. Repeat steps 3-4 until you have completed the observation table on the next page.
Observations:
Colour of Resistor: _______________
Voltage across the
resistor (V)
1
Current through the resistor
(mA)
(A)
Resistance = Voltage (V)
Current (A)
2
3
4
5
7
9
Analysis and Communication:
1. What is the purpose of the ammeter in the circuit?
_____________________________________________________________________
2. What is the purpose of the voltmeter in the circuit?
_____________________________________________________________________
3. a) Name the unit used to measure current. ______________________
b) Name the unit used to measure voltage. ______________________
4. What happens to the current if the voltage increases?
_____________________________________________________________________
5. a) On graph paper, plot the values of voltage and current. Plot voltage (V) on the yaxis (vertical) and current (I) on the x-axis (horizontal).
b) Calculate the slope of the line on your graph. Show work.
c) The slope of the line tells you the amount of ________________ in the circuit.