19.2 CHAPTER 19. ELECTRIC CIRCUITS
- Get your teacher to check the circuit before turning the power on.
- Measure the current.
- Add one more 1,5 Vcell to the circuit and measure the current again.
- Repeat until you have four cells and you have completed your table.
- Draw a graph of voltage versus current.
Results:- Does your experimental results verify Ohm’sLaw? Explain.
- How would you go about finding the resistance of an unknown resistor using only a
power supply, a voltmeter and a known resistor R 0?
Activity: Ohm’s Law
If you do not have access to the equipment necessary for the Ohm’s Lawexperiment, you
can do this activity.
Voltage, V (V) Current, I (A)
3,0 0,4
6,0 0,8
9,0 1,2
12,0 1,6- Plot a graph of voltage (on the x-axis) and current (on the y-axis).
Conclusions: - What type of graph do you obtain (straight line, parabola, other curve)
- Calculate the gradient of the graph.
- Do your experimental results verify Ohm’s Law? Explain.
- How would you go about finding the resistance of an unknown resistor using only a
power supply, a voltmeter and a known resistor R 0?
An important relationship between the current,voltage and resistance ina circuit was discoveredby
Georg Simon Ohm andis called Ohm’s Law.
DEFINITION: Ohm’s Law
The amount of electriccurrent through a metalconductor, at a constanttemperature,
in a circuit is proportional to the voltage across the conductor. Mathematically, Ohm’s
Law is written:
V = R· I.Ohm’s Law tells us thatif a conductor is at a constant temperature, the current flowing through the
conductor is proportional to the voltage across it. This means that if weplot voltage on the x-axis of a
graph and current on the y-axis of the graph, we will get a straight-line. The gradient of the
straight-line graph is related to the resistance of the conductor.