Reducing unwanted energy transfers

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Reducing thermal energy loss in homes

**35%** of heat is lost through **walls**; reduced by **cavity wall insulation** (filling the gap between two walls with insulator).
**25%** is lost through the **roof/attic**; reduced by **loft insulation**.
**25%** is lost through **windows and doors**; reduced by **double glazing**, **curtains**, and **draught excluders**.
**15%** is lost through the **floor**; reduced by improving **floor insulation**.
Reducing heat loss lowers **electricity and fuel bills**.

Cavity wall insulation

A **cavity wall** has two separate walls with a **gap** between them.
The gap is filled with an **insulator** (e.g., foam) to reduce heat transfer.
Insulators like foam contain **trapped air bubbles**, which are poor conductors.

Double glazing

Double glazing uses **two panes of glass** separated by a **gas** (e.g., air or argon).
The gas layer is a **poor conductor**, reducing heat loss through windows.
It also limits **convection** because the gas is trapped.

Other ways to reduce heat loss through windows and doors

**Closing curtains** adds an extra insulating layer.
**Draught excluders** block cold air entering under doors.

Vacuum flasks

**Silvered surfaces** reflect **infrared radiation** back into the liquid (for hot liquids) or away from the liquid (for cold liquids).
A **vacuum** has **no particles**, so it prevents **conduction** and **convection**.
The **plastic lid** is an **insulator**, limiting conduction and preventing **evaporation**.

Reducing radiation with silver surfaces

**Silvered** or shiny surfaces **reflect infrared radiation**.
Takeaway containers are often silvered aluminium to limit heat loss by radiation.
A **silver bottle** keeps a cold liquid cooler for longer than a black one because it reflects radiation away.

Properties of insulators

**Plastic** is a **good insulator** (poor conductor).
**Trapped air** is a good insulator because air is a poor conductor.
A **vacuum** has **no particles**, so it cannot transfer heat by conduction or convection.

Particle arrangement in solids, liquids, and gases. A vacuum has no particles, preventing conduction and convection.

Infrared radiation is reflected by silvered surfaces, reducing heat loss.

Slides

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Practice questions

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1.What percentage of thermal energy loss in a typical home occurs through the walls?
Easy
- A35%
- B25%
- C15%
- D45%
2.Which method is used to reduce thermal energy loss through the roof of a house?
Easy
- ALoft insulation
- BCavity wall insulation
- CDouble glazing
- DDraught excluder
3.Why is it important to reduce thermal energy losses from a home?
Easy
- ATo reduce electricity and fuel bills
- BTo increase the temperature inside
- CTo prevent condensation
- DTo improve air quality
4.Double glazing limits thermal energy loss through windows because the gas between the panes reduces which type of heat transfer?
Medium
- AConduction and convection
- BRadiation only
- CConvection only
- DConduction only
5.Which of the following is a way to reduce thermal energy loss through windows, other than double glazing?
Medium
- AClosing curtains
- BCavity wall insulation
- CLoft insulation
- DFloor insulation
6.Silvered aluminium takeaway containers reduce thermal energy loss because the shiny surface reflects which type of radiation?
Medium
- AInfrared radiation
- BUltraviolet radiation
- CVisible light
- DMicrowaves
7.Two identical metal bottles contain cold liquid. One is black and the other is silver. Which bottle keeps the liquid cooler for longer?
Medium
- AThe silver bottle
- BThe black bottle
- CBoth keep the same temperature
- DIt depends on the liquid
8.Which of the following statements about a vacuum is true?
Medium
- AThere are no particles in a vacuum.
- BA vacuum contains air particles.
- CA vacuum conducts heat well.
- DA vacuum allows convection.

More questions

9.Which of the following statements about plastic is true?
Medium
- APlastic is a good insulator.
- BPlastic is a good conductor.
- CPlastic allows convection.
- DPlastic reflects infrared radiation.
10.Cavity wall insulation made of foam with trapped air bubbles is a good insulator because air is a poor conductor and the trapped air reduces which process?
Hard
- AConvection
- BRadiation
- CEvaporation
- DCondensation
11.In a vacuum flask, the vacuum prevents thermal energy transfer by which methods?
Hard
- AConduction and convection
- BRadiation only
- CConvection only
- DConduction only
12.A vacuum flask keeps cold liquids cool because the silvered surfaces reflect infrared radiation away from the liquid, and the vacuum prevents conduction and convection. Additionally, the plastic lid limits which type of energy transfer?
Hard
- AConduction
- BConvection
- CRadiation
- DEvaporation
13.A house loses 35% of its thermal energy through the walls. If the total energy loss per hour is 12 kWh, how much energy is lost through the walls per hour?
Medium
- A4.2 kWh
- B3.0 kWh
- C4.8 kWh
- D3.5 kWh
14.A student investigates how different thicknesses of loft insulation affect the rate of cooling of hot water in a beaker. The table shows the temperature drop after 10 minutes for each thickness. Which thickness is most effective at reducing thermal energy loss?
Medium
- A5 cm: 12°C drop
- B10 cm: 8°C drop
- C15 cm: 5°C drop
- D20 cm: 3°C drop
15.A vacuum flask has a silvered inner surface. Which statement correctly explains how this reduces thermal energy transfer?
Hard
- AIt reflects infrared radiation back into the liquid.
- BIt prevents conduction through the walls.
- CIt stops convection currents in the liquid.
- DIt absorbs thermal radiation from the surroundings.
16.A house has cavity walls filled with foam insulation containing trapped air bubbles. Why does this reduce thermal energy loss?
Medium
- AAir is a poor conductor and trapped air reduces convection.
- BAir is a good conductor and traps heat.
- CFoam prevents radiation by reflecting it.
- DFoam absorbs thermal energy and releases it slowly.
17.A student places two identical metal cans, one painted black and one silver, containing hot water at 80°C. After 10 minutes, the temperature of the water in the black can is 60°C and in the silver can is 65°C. What can be concluded?
Hard
- AThe silver can emits less infrared radiation than the black can.
- BThe black can emits less infrared radiation than the silver can.
- CBoth cans emit the same amount of infrared radiation.
- DThe silver can absorbs more infrared radiation from the surroundings.
18.In a vacuum flask, the vacuum prevents thermal energy transfer by which two methods?
Medium
- AConduction and convection
- BConduction and radiation
- CConvection and radiation
- DEvaporation and radiation
19.Which of the following is a method to reduce thermal energy loss through windows?
Easy
- ADouble glazing
- BCavity wall insulation
- CLoft insulation
- DFloor insulation
20.What percentage of thermal energy loss in a typical home occurs through the roof?
Easy
- A25%
- B35%
- C15%
- D45%
21.A student measures the temperature of a hot drink in a vacuum flask and in a regular cup over 30 minutes. The graph shows temperature vs. time. Which statement is correct?
Medium
- AThe drink in the vacuum flask cools more slowly because it reduces all three types of heat transfer.
- BThe drink in the vacuum flask cools more slowly because it only reduces conduction.
- CThe drink in the regular cup cools more slowly because it is a better insulator.
- DBoth cool at the same rate because the starting temperature is the same.
22.A house loses 25% of its thermal energy through windows and doors. To reduce this, which combination of measures is most effective?
Medium
- ADouble glazing and draught excluders
- BCavity wall insulation and loft insulation
- CLoft insulation and double glazing
- DFloor insulation and cavity wall insulation
23.A vacuum flask is used to keep a cold drink cold. Which of the following features helps keep the drink cold?
Hard
- ASilvered surfaces reflect infrared radiation away from the liquid.
- BThe vacuum allows conduction to occur.
- CThe plastic lid is a good conductor of thermal energy.
- DThe silvered surfaces absorb infrared radiation from the liquid.
24.A house has cavity walls. Which of the following best describes a cavity wall?
Medium
- ATwo separate walls with a gap between them that can be filled with insulation.
- BA single thick wall made of insulating material.
- CA wall with a layer of foam on the outside.
- DA wall with a reflective layer on the inside.
25.A student investigates how different thicknesses of loft insulation affect the cooling of hot water in a beaker. Which piece of equipment is most essential to measure the temperature change?
Medium
- AThermometer
- BBalance
- CRuler
- DStopwatch
26.In an experiment to test the effectiveness of different insulating materials, a student wraps beakers of hot water with different materials and records the temperature every 5 minutes for 30 minutes. Which variable must be kept the same to ensure a fair test?
Hard
- AThe initial temperature of the water
- BThe thickness of the insulating material
- CThe type of insulating material
- DThe volume of water in each beaker
27.A student places two identical metal cans, one painted black and one painted silver, containing equal amounts of hot water at 80°C. After 10 minutes, the temperature of the water in the black can is 65°C and in the silver can is 70°C. What conclusion can be drawn?
Medium
- ABlack surfaces are better emitters of infrared radiation than silver surfaces.
- BSilver surfaces are better emitters of infrared radiation than black surfaces.
- CBlack surfaces absorb more infrared radiation from the surroundings.
- DSilver surfaces reflect less infrared radiation than black surfaces.
28.A student investigates how the thickness of loft insulation affects the rate of cooling of hot water in a beaker. The table shows the temperature drop after 20 minutes for different thicknesses: Thickness (cm): 0, 2, 4, 6 Temperature drop (°C): 25, 18, 14, 12 Which conclusion is supported by the data?
Hard
- AIncreasing thickness reduces heat loss, but the effect diminishes with greater thickness.
- BIncreasing thickness increases heat loss.
- CHeat loss is directly proportional to thickness.
- DThickness has no effect on heat loss.
29.A vacuum flask keeps cold liquids cold. Which feature helps keep the liquid cold?
Medium
- ASilvered surfaces reflect infrared radiation away from the liquid.
- BSilvered surfaces reflect infrared radiation into the liquid.
- CThe vacuum allows convection currents to form.
- DThe plastic lid conducts heat into the liquid.
30.What is cavity wall insulation used to reduce?
Easy
- AThermal energy loss through walls
- BThermal energy loss through windows
- CThermal energy loss through the roof
- DThermal energy loss through the floor
31.Which of the following is a method to reduce thermal energy loss through the roof?
Easy
- ALoft insulation
- BDouble glazing
- CDraught excluder
- DCavity wall insulation
32.What percentage of thermal energy loss in a typical home occurs through the floor?
Easy
- A15%
- B25%
- C35%
- D10%
33.A vacuum prevents thermal energy transfer by which method?
Easy
- AConduction and convection
- BConduction only
- CConvection only
- DRadiation only
34.Which of the following statements is true?
Easy
- AThere are no particles in a vacuum.
- BPlastic is a good conductor.
- CSilvered surfaces increase thermal energy loss.
- DA vacuum allows convection.
35.Why does a silvered surface in a vacuum flask help keep a hot liquid hot?
Medium
- AIt reflects infrared radiation back into the liquid.
- BIt absorbs infrared radiation from the surroundings.
- CIt prevents conduction through the walls.
- DIt reduces convection currents.
36.Cavity wall insulation contains trapped air bubbles. Why does this make it a good insulator?
Medium
- AAir is a poor conductor and trapped air reduces convection.
- BAir is a good conductor and trapped air increases conduction.
- CAir is a poor conductor and trapped air increases convection.
- DAir is a good conductor and trapped air reduces radiation.
37.Which of the following helps keep a cold drink cold in a vacuum flask?
Medium
- ASilvered surfaces reflect infrared radiation away from the liquid.
- BSilvered surfaces reflect infrared radiation into the liquid.
- CThe vacuum allows convection currents to form.
- DThe plastic lid is a good conductor.
38.A student places two identical metal cans, one black and one silver, containing hot water at 80°C. After 10 minutes, which can will have the higher temperature?
Medium
- AThe silver can
- BThe black can
- CBoth will be the same
- DIt depends on the volume of water
39.In a vacuum flask, which feature reduces thermal energy loss by evaporation?
Hard
- APlastic lid
- BSilvered surfaces
- CVacuum
- DDouble-walled construction
40.A house loses 35% of its thermal energy through walls. If the total energy loss is 20 kWh per hour, how much energy is lost through the walls per hour?
Hard
- A7 kWh
- B5 kWh
- C9 kWh
- D12 kWh

Revision notes

## Reducing Unwanted Energy Transfers ### Home Insulation - **Walls (35% loss)**: Cavity wall insulation fills the gap between two walls with an insulator. - **Roof/attic (25% loss)**: Loft insulation reduces heat loss. - **Windows/doors (25% loss)**: Double glazing (two panes with gas gap), curtains, and draught excluders help. - **Floor (15% loss)**: Improve floor insulation. ### Vacuum Flask - **Silvered surfaces** reflect infrared radiation back into hot liquid (or away from cold liquid). - **Vacuum** prevents conduction and convection (no particles). - **Plastic lid** is an insulator, limits conduction and prevents evaporation. ### Key Points - Reducing thermal energy loss lowers electricity and fuel bills. - Trapped air (e.g., in foam) is a good insulator because air is a poor conductor. - Silver surfaces reflect radiation; black surfaces absorb and emit radiation well. - Double glazing limits conduction and convection via the gas gap. - Draught excluders stop air flow under doors. ### True/False - Vacuum has no particles → True - Plastic is a good conductor → False (it is an insulator)

Cavity wall insulation: Filling the gap between two walls with an insulator to reduce thermal energy loss through walls.
Loft insulation: Insulation in the roof/attic to reduce thermal energy loss.
Double glazing: Two panes of glass separated by a gas to limit thermal energy loss through windows.
Draught excluder: A device placed at the bottom of a door to stop draughts and reduce heat loss.
Vacuum flask: A container designed to limit thermal energy transfers using silvered surfaces, a vacuum, and an insulating lid.
Silvered surfaces: Reflective surfaces that reflect infrared radiation to reduce heat transfer by radiation.
Vacuum: A space with no particles, preventing conduction and convection.

Flashcards

What percentage of thermal energy loss in a home is through the walls?

35%.

How can thermal energy loss through walls be reduced?

By installing cavity wall insulation, which fills the gap between two walls with an insulator.

What percentage of thermal energy loss in a home is through the roof/attic?

25%.

How can thermal energy loss through the roof be reduced?

With loft insulation.

What percentage of thermal energy loss in a home is through windows and doors?

25%.

Name three ways to reduce thermal energy loss through windows and doors.

Double glazing, closing curtains, and using a draught excluder.

What percentage of thermal energy loss in a home is through the floor?

15%.

How can thermal energy loss through the floor be reduced?

By improving the insulation in the floor.

Why is it important to reduce thermal energy losses from a home?

To reduce the size of electricity and fuel bills.

How does double glazing limit thermal energy loss?

It consists of two panes of glass separated by a gas, which reduces conduction and convection.

State a way, other than double glazing, to reduce thermal energy loss through windows.

Closing curtains.

Why do silvered aluminium takeaway containers limit thermal energy loss due to radiation?

Silvered surfaces reflect infrared radiation, reducing heat transfer by radiation.

Which bottle keeps a cold liquid cooler for longer: black or silver? Explain.

The silver bottle, because its shiny surface reflects infrared radiation away from the liquid, reducing heat gain.

True or false: There are no particles in a vacuum.

True.

True or false: Plastic is a good conductor.

False. Plastic is a good insulator.

Why is foam with trapped air bubbles a good insulator for cavity walls?

Air is a poor conductor, and the trapped air reduces convection and conduction.

What feature of a vacuum flask reflects infrared radiation back into the liquid?

Silvered surfaces.

How does the vacuum in a vacuum flask reduce thermal energy transfer?

It prevents conduction and convection because there are no particles.

What is the role of the plastic lid in a vacuum flask?

It is an insulator that limits conduction and also prevents evaporation.

How does a vacuum flask keep a cold liquid cooler for longer?

Silvered surfaces reflect infrared radiation away from the liquid, the vacuum prevents conduction and convection, and the plastic lid limits conduction.

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