DSE Physics | Specific Heat Capacity Lesson-Prep Guide (Tutor Edition)

DSE Physics | Specific Heat Capacity Lesson-Prep Guide (Tutor Edition) | E = mc dT and Heating Time

2026-11-01

Tutor lesson-prep guides · Secondary Physics

Students can write E = mc dT but cannot explain why the sea stays cooler than the land. Heat water and oil with the same heater and “large specific heat capacity” becomes something they have seen.

Objectives — Students can: (1) compute heat energy with E = mc dT; (2) turn energy into time using power and efficiency; (3) explain one example each of conduction, convection and radiation, and match the three features of a vacuum flask to the transfer route each one blocks.

01 Prerequisites (3-minute check)

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

Skill	Quick check	Pass mark
Power	What does 1 W mean?	One joule per second
Mass units	What is 500 g in kg?	0.5 kg
Temperature change	From 20 to 40 degrees Celsius, what is dT?	20 degrees

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-8 min	Demo: water and oil	Same heater, who heats faster?	Predict, then test
8-22 min	E = mc dT	Units of each symbol	Obtain 42 kJ
22-36 min	Energy to time	Power and efficiency	Obtain 105 s
36-48 min	Three transfer routes	Conduction, convection, radiation	One example each
48-56 min	Vacuum flask	Match each feature to a route	Name all three
56-60 min	Exit check	Three questions, marked at once	Independent work

03 Teaching script (read it out)

Scene 1: Heating curves: steeper means smaller capacity

The same 500 W heater warms oil faster than water because oil has a smaller specific heat capacity. Warming 0.5 kg of water by 20 degrees takes 0.5 times 4200 times 20 = 42000 J.

Ask them: why does the daytime breeze blow from sea to land? Water heats slowly, land air rises first.

Scene 2: From energy to time: use the net power

500 W means 500 J every second, so 42000 J needs 84 s in an ideal case. With 80% efficiency it is 42000 divided by (500 times 0.8) = 105 s.

Watch this: losses mean more time, so you divide by efficiency, never multiply.

Scene 3: Conduction, convection, radiation: three routes, three blocks

Conduction moves energy by particle collisions and is best in metals. Convection moves it with the fluid itself. Radiation is electromagnetic and needs no medium, working best from dark rough surfaces. A vacuum flask blocks all three: the vacuum stops conduction and convection, the silvered walls reflect radiation, the stopper stops convection at the top.

Interview-style prompt: why is a down jacket warm? Trapped air cuts conduction and convection; the jacket does not generate heat.

04 Question types and worked steps

Type	Example	Steps	Answer
Calculation	E = mc dT	0.5 x 4200 x 20	42000 J
Calculation	Ideal heating time	E divided by P	84 s
Calculation	Time with efficiency	E divided by (P x efficiency)	105 s
Application	Three features of a flask	One route each	Vacuum, silver, stopper

Sanity check (teach this): The unit of c is J per kg per K, so mass must be in kg and dT is a difference: never add 273. Check the order of magnitude – a few hundred grams of water rising tens of degrees is tens of thousands of joules.

05 Independent practice (3 questions)

Question	Answer	What to watch
Energy to warm 0.5 kg of water by 20 degrees	42000 J	E = mc dT
Time with a 500 W heater	84 s	E divided by P
Time at 80% efficiency	105 s	Net power is 400 W

06 Common mistakes and what to say

Mistake	Student writes	Say this
Using grams for mass	Writing 500 instead of 0.5	c is per kilogram, so 500 g must become 0.5 kg.
Adding 273 to dT	Using 293 K as the difference	Only the difference matters: 20 degrees is 20 K.
Multiplying by efficiency	84 times 0.8	Losses make it slower, so divide by efficiency.
Thinking radiation needs a medium	Saying a vacuum cannot lose heat	Radiation is electromagnetic; that is how the Sun reaches us.

07 Homework (paper, section and question numbers)

DSE Physics practice paper (heat section) — Questions 7-10
Secondary Physics chapter index — All chapters

08 Exit check (last 5 minutes)

Question	Answer	Decision
Energy to warm 0.5 kg by 20 degrees	42000 J	Three correct: move on to change of state
Heating time at 500 W	84 s	One wrong: re-teach units
What does the silvered wall do?	Reflects radiation	Two or more wrong: restart act one

09 Tutor FAQ

Must students memorise c?

Only water, 4200 J per kg per K. Other values are given in the question.

Why does metal feel cold?

It conducts heat away from your finger quickly; it is not at a lower temperature. That is the standard conduction answer.

Can efficiency exceed 100 per cent?

No. If it does, joules and kilowatt-hours have been mixed.

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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.