Year 9 Science · Unit 3 · Lesson 20
Challenge Worksheet
Learning Goals
Read the graph
The bar chart shows the current drawn by five common Australian household appliances, all connected to 240 V mains. Use the graph to answer the questions.
Data: Calculated from I = V ÷ R for appliances at 240 V Australian mains supply.
(a) The Australian household circuit safety limit is 10 A. Which appliance(s) exceed this limit? What would happen if they were switched on?
(b) The TV (240 Ω) draws far less current than the microwave (34.3 Ω) even though both use 240 V. Use Ohm's Law to explain this difference.
Find the mistake
A student wrote this explanation of circuits
"To measure voltage, you connect a voltmeter in series with the component. In a series circuit, each component gets the same voltage from the battery. Ohmic conductors are different from normal conductors because their resistance increases with temperature. Finally, if one branch of a parallel circuit breaks, the entire circuit stops working because there is no longer a complete path."
1. There are four errors in the student's explanation, one from each lesson (L17, L18, L19, L19/L18). List all four errors clearly.
2. Write a corrected version of each error. For each correction, name the scientific principle that makes the original statement wrong.
Wrap Up
In one sentence, what was the main idea of this lesson?