Primary General Studies｜Energy and Saving Electricity: Tutor Prep Guide

2026-11-13

Tutor lesson-prep guides · Primary General Studies

Students can say that saving energy matters, yet none of them know how many units their home uses in a month. Saving energy stays a slogan because it never becomes a number. This lesson does one thing: power multiplied by time gives units, and units multiplied by price give money. Once a student computes 180 units and 216 dollars for one air conditioner, saving energy becomes something they control.

Objectives — Students can: (1) compute energy use as power in kW multiplied by hours, and convert units into a cost; (2) explain that most Hong Kong electricity comes from burning fossil fuels, so saving energy also cuts emissions; (3) name four ways to save energy (efficient appliances, less run time, adjusted settings, standby off) with one home example each; (4) give two limits of solar and wind power and explain why fossil fuels remain necessary.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Multiplying decimals	What is 1.5 times 4	Answers 6
Units	How many kilowatts is 1,000 watts	Answers 1 kW
Everyday electricity	Name two appliances that use electricity at home	Names air conditioner, fridge, lights

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0–6 min	Opening estimate	Ask how many units a home uses monthly	Write an estimate to revisit
6–18 min	Where power comes from	Fuel, turbine, transmission	Explain why saving energy cuts pollution
18–34 min	What a unit is	1,500 W for 4 hours equals 6 units	Compute a second appliance
34–44 min	Four ways to save	Four categories, one home example each	Write three actions for their room
44–54 min	Limits of renewables	Two limits each for solar and wind	Explain why they cannot replace all
54–60 min	Exit check	Three quick questions, name the error type	Answer independently

03 Teaching script (read it out)

Scene 1: Electricity comes from fuel, not from the socket

Break the picture first: a socket is only an interface. Power is generated at a plant, in Hong Kong mainly by burning coal and natural gas to drive turbines. Write three steps on the board: fuel burns, turbine turns, power is transmitted. Then ask what burning produces: carbon dioxide and pollutants. So saving energy has two meanings, money and emissions, and this sentence must be said twice because students remember only the money. Mention nuclear imports and renewables in one line without detail; the point is that most power still comes from burning.
Students do: draw the three-step chain and write one emission beside step one.

Students say: one sentence on why saving energy is also environmental protection.

Scene 2: A unit of electricity: one multiplication carries the lesson

One unit is 1 kW used for 1 hour, so there is only one formula: power in kW multiplied by hours gives units. Air conditioner: 1,500 W is 1.5 kW, run for 4 hours, giving 1.5 times 4 equals 6 units. At an assumed 1.2 dollars per unit that is 7.2 dollars a night, and 180 units or 216 dollars across 30 days. Students must press the calculator themselves; the tutor does not write the answer first. Then the lamp comparison: a 12 W LED for 5 hours is 0.06 units, a 60 W filament lamp for the same 5 hours is 0.30 units, a saving of 0.24 units or 80 percent. Same job, one fifth of the electricity, which persuades far better than telling students to switch lights off. Close on units: divide watts by 1,000 for kW, and minutes by 60 for hours.
Students do: pick one appliance at home and compute its daily units and monthly cost.

Students say: the formula in one sentence they can remember.

Scene 3: Four ways to save, and why renewables cannot do it alone

Group saving actions into four kinds with one home example each: efficient appliances (inverter air conditioner, LED lamps); less run time (sleep timer, switch off on leaving); adjusted settings (cooling at 25.5 degrees, keep the fridge door shut); standby off (television and chargers). Students sort the actions themselves, because exam questions give an action and ask which category it belongs to. Then renewables: solar depends on weather and daylight and needs large areas; wind depends on wind speed and faces siting and noise limits. Hence the practical order is reduce first, replace second, add renewables third.
Students do: sort six actions into the four categories and write three they can do today.

Students say: one limit each for solar and wind, and why saving energy still matters.

04 Question types and worked steps

Type	Example	Steps	Answer
Calculation	A 1,500 W air conditioner runs 4 hours: how many units	Watts divided by 1,000, then multiplied by hours	The unit must be stated
Comparison	Two lamps over the same 5 hours: percentage saved	Compute both, then difference over original times 100	The percent sign is required
Classification	Sort five actions into four saving methods	Ask which of the four each action changes	Reasons accompany the sorting
Explanation	Why solar cannot fully replace fossil fuels	Two limits plus one conclusion	Named limits, not “not enough”

Sanity check (teach this): One formula, power times hours, carries every calculation, so students do not memorise several. The price is assumed at 1.2 dollars and must be labelled as assumed so nobody mistakes it for a real bill. The lamp comparison uses identical run time so the percentage reflects power alone. Each of the four saving methods needs a home example, or students memorise names without meaning. Renewables stop at two limits, which is the primary scope.

05 Independent practice (3 questions)

Question	Answer	What to watch
Units	A 600 W rice cooker runs half an hour: how many units	Checks the divide by 1,000 happens first
Cost	The same half hour at 1.2 dollars per unit	Checks units and decimals
Sorting	Three actions they can take, each sorted	Checks coverage of the four categories

06 Common mistakes and what to say

Mistake	Student writes	Say this
Watts multiplied directly	“1,500 times 4 is 6,000 units”	“Divide watts by 1,000 first. 1.5 kW for 4 hours is 6 units.”
Minutes used as hours	“It ran 30 minutes, so multiply by 30”	“30 minutes is half an hour, so use 0.5.”
Saving energy means saving money only	“We save energy to cut the bill”	“The bill is one part. Less electricity means less fuel burned and fewer emissions.”
Solar can replace everything	“With enough solar we need no power station”	“No sun at night or in rain, and panels need space. So we reduce use first.”

07 Homework (paper, section and question numbers)

P5 General Studies paper with answers — Questions 4 and 6: energy sources and saving methods
P6 General Studies paper with answers — Questions 3 and 8: electricity calculations and renewable limits

08 Exit check (last 5 minutes)

Question	Answer	Decision
Define one unit of electricity	1 kW used for 1 hour	Re-teach if wrong
How many units for 1,500 W over 4 hours	6 units	Demonstrate the sum if wrong
One limit of solar power	No generation at night or in heavy cloud, or large area needed	Supply it if missing

09 Tutor FAQ

Should real tariffs be used?

No. Tariffs carry tiers and surcharges that primary students cannot handle. An assumed 1.2 dollars per unit keeps the focus on multiplication and units.

Should nuclear power be taught here?

One sentence that part of Hong Kong supply is imported nuclear is enough. The lesson is about measurable electricity use and the two meanings of saving energy.

What if the class is weak at decimals?

Stay on the whole-number case, 1 kW for 1 hour, until it is secure. Do not push four examples when the multiplication is not yet reliable.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.

Practice papers　Paper 1 (basics)　·　Paper 2 (intermediate)　·　Paper 3 (challenge)　·　Paper 4 (error clinic)