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Year 9 Advanced Science
Calculation involving Ohm’s Law
Name: _________________________________________
Background information:
For many devices, the resistance is constant regardless of the current. In this case, the potential difference is directly
proportional to the current:V = I · R
This is known as Ohm's law. Any device that follows Ohm's law is called an "ohmic" device;
A device that does not obey Ohm's law is said to be "non-ohmic".
A resistor is a device that provides a fixed resistance in a circuit.
A light bulb is a non-ohmic device.
The filament of a normal bulb is made from tungsten. Tungsten’s resistance will increase with temperature.
When a voltage is applied across the filament current flows through it, the temperature will increase so the resistance
also increases. Then current then decreases proportional to the change in resistance.
If the voltage applied is increased then the initial current also increases, but it still decreases as the temperature rises.
Complete the following questions using Ohm’s Law
1. Define Ohm’s Law.
2. Which of the following graphs depict ohm's law. Circle the correct answer. Draw the curve for a light
bulb with non-ohmic relationship.
3. A resistance of 10 Ω is placed across a 9 V battery. What current flows through the battery?
4. A resistor has a resistance of 10Ω, what voltage is needed to cause a 500 mA current to flow through the circuit?
5. What is the overall resistance of a CD portable player if it is operated by a 3 V battery and 0.75 A flow through its
6. A 9 volt battery supplies power to a cordless curling iron with a resistance of 18 ohms. How much current is flowing
through the curling iron?
7. A 240 volt wall outlet supplies power to a strobe light with a resistance of
2200 ohms. How much current in milliamperes (mA) is flowing through the
strobe light? Why the resistance is so large in a strobe light?
8. What value of resistor would be used to permit a current of 0.2A to flow using a 6V supply?
9. What supply voltage would be needed to provide a current of 1.2A through a 40 ohm resistor?
10. What current would flow through a resistor of 40 ohms connected to a 10V supply?
11. Find the size of resistor which would limit the current to a value of 0.02A when connected to an 8V
12. What current would flow through a resistor of 1.2 kΩ connected to a 240V supply?
13. Calculate the current in milliamperes (mA) which will flow when a total resistance of 500 ohms is
placed in a circuit which has a 15 Volt supply.
14. The resistance of a wire is directly proportional to its length. If 200 km of wire has resistance of 10 Ω,
what is the voltage or potential difference between the end if the wire is 200m in length and the ammeter
reading is 1200A.
15. A resistor allows a current of 0.6A to flow when connected to a 9.6V volt supply. What current would
flow if the same resistor was connected to a 12.8V supply?
First of all, find the resistance of the resistor first:
16. Name 3 factors that affect the resistance of a conductor such as a wire.
17. When components are connected in series, their total resistance is the sum of their individual
Find the total resistance of these 3 resistors connected in series.
18. Explain why the lamps become dimmer when more are connected in series. What happens when the
lamps are connected in parallel?