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Station 2
Ohms Law
Outcomes:
 State Ohms Law
 Given voltage drop and current through a resister, calculate its resistance
 Given voltage drop and resistance, calculate current through a resistor
 Given current through a resistor and its resistance, calculate voltage drop
Suggested Activities:
Construct a circuit to include a battery, resister (such as a lamp) and an
ammeter. Explore what happens when other resistors are added i.e. more lamps.
Could add batteries to explore voltage and current readings. This would show
relationships between current, voltage and resistance and discover that the
amount of current in a circuit is directly proportional to the voltage and is
inversely proportional to the resistance. This leads to an understanding of Ohms
Law.
Explanation:
Electrical resistance is the ratio of the voltage to the current. The unit of
measurement for electrical resistance is the ohm (). The mathematical
relationship comparing voltage (V), current (I), and resistance (R) is called
Ohm’s law and is written as:
R = V/I
Ohm’s law is more commonly written in the form:
V = IR
You can use Ohm’s law to calculate resistance.
Source: Discovering Science 9 & Dept. of Education, NL, Science 9 Curriculum Guide
Sample Calculation:
1. What is the resistance of a flashlight bulb if there is a current of 0.75 A through the
bulb when connected to a 3.0 V battery?
Use the formula:
R = V/I
R = 3.0V / 0.75A
= 4.0 
State your answer:
The resistance of the flashlight bulb is 4.0 .
Practice Problems:
1. The current through a load in a circuit is 1.5 A. If the potential difference across the load is
12 V, what is the resistance of the load?
Answer: 8 
2. The resistance of a car headlight is 15 . If there is a current of 0.80 A through the
headlight, what is the voltage across the headlight?
Answer: 12 V
3. A 60 V potential difference is measured across a load that has a resistance of 15 . What
is the current through this load?
Answer: 4 A
Source: Discovering Science 9 & Dept. of Education, NL, Science 9 Curriculum Guide