Energy Efficiency and Real-Life Use

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Energy Efficiency and Real-Life Use — Free MYP2 Sciences Practice Questions

1QuestionCalculating Efficiency PercentConcept Practice

3 marks~5 minCriterion A

The bar graph below shows the efficiency of three light bulbs. Efficiency (%) is the percentage of electrical energy converted into useful light energy.

Identify which bulb has the highest efficiency. [1]

Explain why the incandescent bulb has the lowest efficiency. [1]

The LED efficiency is about 80% and the incandescent efficiency is about 10%. Compare the energy wasted as heat by each bulb. [1]

Solutions

2QuestionEnergy Labels and Appliance RatingsAssessment Practice

5 marks~8 minCriterion C

Four refrigerator models were tested. Efficiency (how much of the energy put in becomes useful output) is calculated as:

\text{Efficiency} = \frac{\text{useful output (J)}}{\text{total input (J)}} \times 100\%

Model	Energy input (J)	Useful output (J)	Labelled rating
A	800	600	$A^{+++}$
B	1200	720	$A^{+}$
C	1500	750	B
D	2000	800	D

Energy rating thresholds:

A^{+++}

≥ 70%,

A^{+}

≥ 55%, B ≥ 45%, C ≥ 35%, D < 35%.

Calculate the efficiency of Model A. [1]

Calculate the efficiency of each remaining model (B, C, and D). [2]

Compare the calculated efficiencies of all four models with their labelled ratings. Identify which model has an inconsistent rating and explain why. [2]

Solutions

3QuestionCalculating Efficiency PercentAssessment Practice

6 marks~9 minCriterion D

A 60 W incandescent bulb has an efficiency of 2%. A 12 W LED bulb has an efficiency of 80%. Both bulbs are used for 4 hours each day.

Efficiency is the percentage of energy input that becomes useful light energy.

Calculate the energy wasted per day by each bulb in watt-hours (Wh). Show your working. [2]

Explain one environmental benefit and one financial benefit of switching from the incandescent bulb to the LED bulb. [2]

Compare efficiency with two other factors a consumer should consider when choosing a light bulb. [2]

Solutions

4QuestionCalculating Efficiency PercentAssessment Practice

5 marks~8 minCriterion B

An electric toy car is tested with different numbers of toy passengers. Efficiency (%) shows how much input energy becomes useful output energy.

Number of passengers	0	1	2	3
Input energy (J)	100	120	150	180
Output energy (J)	90	100	110	115

Calculate the efficiency percentage for each number of passengers using:

\text{efficiency} = \frac{\text{output energy}}{\text{input energy}} \times 100\%

[2]

Describe the pattern in efficiency as the number of passengers increases. [1]

Estimate the efficiency for 4 passengers and explain your reasoning using the pattern you identified. [2]

Solutions

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