Year 9 Science · Unit 3 · Lesson 19
Challenge Worksheet
Learning Goals
Read the graph
The bar chart below shows the current produced by three different resistors at four different voltages. Use it to answer the questions below.
Data: Simulated Ohm's Law investigation results, ohmic resistors at constant temperature.
(a) Which resistor produces the steepest increase in current as voltage increases? What does a steeper increase tell you about its resistance?
(b) For Resistor A, when voltage doubles from 4 V to 8 V, what happens to the current? Is this the behaviour expected from an ohmic conductor?
Evaluate the claim
A student claims...
"A light bulb must follow Ohm's Law because you can always measure the voltage across it and the current through it, then use R = V/I to calculate its resistance. Since you can calculate R for any values of V and I, Ohm's Law must apply."
(a) What part of the student's reasoning is correct? What can always be calculated for any component?
(b) Explain the flaw in the student's argument. What is the key difference between a material that truly obeys Ohm's Law and one where you can still calculate R = V/I but Ohm's Law does not apply?
(c) Describe what a V-I graph would look like for: (i) an ohmic conductor; (ii) a light bulb filament (non-ohmic). Use the idea of resistance staying constant or changing.
Wrap Up
In one sentence, what was the main idea of this lesson?