Name: _______________________________
Date: _____________________
SNC 1D
Discovering Ohm’s Law
Introduction
For a circuit to be complete it must include connecting wires, a power source, and a load. The
power source provides coulombs with energy which is measured in ________. The coulombs decrease
in energy as they pass through the load, providing the load with energy to create light, heat or perform
some sort of action. The connecting wires create a path allowing the coulombs to flow through the
circuit. The amount of coulombs moving through a point in the circuit in a certain amount of time is
referred to as the __________. ___________ is measured by an ammeter which is connected inside the
circuit. __________ (potential difference) is the amount of energy per coulomb of charge between 2
different points in the circuit. It is measured by a voltmeter which is connected across two points in a
circuit outside of the circuit (connected in parallel).
In this lab, you will be changing the voltage and then recording the current changes. The independent
variable is __________________________ and the dependent is _____________________________.
Purpose:
To identify both qualitatively and quantitatively how voltage affects current and to draw a conclusion
about Ohm’s law.
Materials:
Ammeter
Wires
Voltmeter
25  resistor
Power source
Switch
Method: (Following along with the methods as your teacher performs the steps)
*SAFETY CONCERNS*:
Make sure the switch is open before you connect the meters and that you do not create a short circuit
(ie. Make sure you have a load)
Build a series circuit with: 25 Ω resistor, 1 ammeter, wires, power source, and a switch.
Connect a voltmeter across the resistor.
Turn the power source on to its lowest voltage and close the switch.
Measure the voltage with the voltmeter and the current with the ammeter. Record your measurements in
Table 1.
E) Increase the voltage slightly and repeat each step until you have 5 measures recorded.
A)
B)
C)
D)
Observations – Fill in the table below
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Table 1: ______________________________________________________________
Voltage (V)
Current (A)
Data Analysis and discussion
1) Open Excel and plot the data on an xy graph. The x data is voltage and y data is current. This
will be done with the teachers guidance.
2) What qualitative statement can you make about the effect of voltage on current?
_______________________________________________________________________________
_______________________________________________________________________________
3) Make a quantitative statement about the effect of voltage on current.
__As the voltage was doubled, the current____________________________________________
_______________________________________________________________________________
4) Slope can be calculated by dividing the rise (y2-y1) by the run (x2-x1). Since there is a (0,0)
point, we can get the slope by dividing y (voltage) by x (current). Complete the following table
using your values.
Table 1: ______________________________________________________________
Voltage (V)
Current (A)
2
V/I
5) Make a qualitative statement about how voltage affects the the V / I results.
_______________________________________________________________________________
_______________________________________________________________________________
6) What do you think this V / I value tells us about the resistor?
_______________________________________________________________________________
_______________________________________________________________________________
7) Make a conclusion about Ohm’s Law.
_______________________________________________________________________________
_______________________________________________________________________________
8) What is the formula for Ohm’s law?
Ohm’s Law Questions
1) A refrigerator draws a current of 12 A and uses 110 V. Find it’s resistance. Use GRASP.
2) Find the current of a 6.0 V flashlight if has a resistance of 30 Ω. Use GRASP.
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