Year 9 Science · Unit 3 · Lesson 3

Calculating Energy Conservation

Foundation Worksheet

Name
Date
Class

Learning Goals

Warm Up

Recall 5 marks

True or False? Fix the false ones

Circle T or F for each statement. If the statement is false, rewrite it correctly on the line below.

Efficiency can exceed 100% if a device is designed well enough.

Correct it:

T
F

If the useful energy output of a device is 800 J and the input is 1,000 J, the efficiency is 80%.

Correct it:

T
F

Waste energy permanently disappears and cannot be measured or accounted for.

Correct it:

T
F

If efficiency is 40% and input is 1,000 J, the waste energy is 600 J.

Correct it:

T
F

The word equation "Input energy = Useful output + Waste output" is a restatement of the law of conservation of energy.

Correct it:

T
F

Your Turn

Recall 10 marks

Sort it!

Three energy scenarios are described below. Write each energy value from the pool into the correct column in the table.

600 J (waste heat from hair dryer) 1,000 J (electrical input to hair dryer) 400 J (useful thermal output of hair dryer) 500 J (chemical input to camp stove) 350 J (useful thermal energy to pot) 150 J (waste heat from camp stove) 200 J (electrical input to LED globe) 50 J (useful light output of LED globe) 150 J (waste heat from LED globe) 2,000 J (chemical input to petrol engine)

Input energy

Useful output energy

Waste energy

Show What You Know

1. A lamp receives 200 J of electrical energy and produces 50 J of light. Calculate (a) the waste energy and (b) the efficiency of the lamp. Show your working.

Recall 2 marks

2. A student says: "The efficiency of my phone charger is 95%, so hardly any energy is wasted, it's basically perfect." Do you agree? Explain using the definition of efficiency.

Recall 2 marks

Wrap Up

In one sentence, what was the main idea of this lesson?

HSCScience · Year 9 Science · Unit 3 · Lesson 3 · Foundation Worksheet