P2: Energy Transfer By Heating (Y10 - Summer 1)

Question 1

🟢 What is Thermal Conductivity?

Answer 1

Thermal Conductivity of a material refers to the rate at which it will transfer heat energy.

Question 2

🟢 What is Insulation?

Answer 2

Insulation means to reduce the amount of energy transfer across a material. Therefore insulation is to reduce the rate of heat energy transfer.

Question 3

🟢 What does the energy transfer per second through a layer of insulating material depend on?

Answer 3

It depends on:

• The temperature difference across the material
• The thickness of the material
• The thermal conductivity of the material

Question 4

🟢 How to reduce the energy transfer as much as possible?

Answer 4

1. The thermal conductivity of the insulating material should be as low as possible
2. The thickness of the insulating layer should be as thick as is practically possible.

When an isulating material is chosen for a roof, the insulating material has a much lower thermal conductivity than the roof material. Several layers of this material fitted on the loft floor will reduce the energy transfer through the roof significantly.

Question 5

🟢 Why can objects be hot or cold to touch but are actually at the same temperature?

Answer 5

Objects can feel hotter or colder than one another, but can easily be the same temperature. This is dependant on how well the material can conduct.

This is shown by the fact that metals will feel colder because it conducts the heat energy from your hand that’s touching it quicker. Thid will be the opposite for bad conductors which will feel warmer when you touch it because it is conducting the heat at a slower rate.

Question 6

🟢 What Types of Waves come from the Sun

Answer 6

When you are in sunlight, you are absorbing infrared radiation from the Sun. infrared radiation and bisinle light are parts of the electromagnetic spectrum. So too are radio waves, microwaves, ultraviolet rays, and X-rays. Electromagnetic waves are electric and magnetic waves that travel through space. The wavelength of light increases across the visible spectrum from blue to red light. Infrared waves are longer in wavelength than visible light.

The Sun emits all types of electromagnetic radiation. Fortunately, the Earth’s atmosphere blocks most of the types of radiation that are harmful to people. But it doesn’t block infrared radiation or light from the Sun.

Question 7

🟢 How can you detect Infrared Radiation

Answer 7

You can use a thermometer with a blackened bulb to detect infrared radiation.

This is done when a glass prism splits a narrow beam, of white light into the colours of the spectrum.

The thermometer reading rises when it is placed just beyond the red part of the spectrum. Some of the infrared radiation in the beam goes there. Your eyes can’t detect it, but the thermometer can.

Infrared radiation is beyond the red part of the visible spectrum.

Question 8

❌ How does Colour affect Radiation

Answer 8

A perfect black body is an onject that absorbs all the radiation that hits it. It doesn’t reflect any radiation, and it doesn’t transmit (i.e, no radiation passes through it). A good absorber is also a good emitter, so a perfect black body is also the best possible emitter. The radiation emitted by a perfect black body is called black body radiation. No other object emits or absorbs radiation as effectively as black body.

Question 9

❌ How does Higher/Increasing Temperatures affect Radiation

Answer 9

The higher the temperature of an object, the more infrared radiation it emits in a given time.

If the temperature of the object is increased, the intensity of the radiation it emits is greater at every wavelength. This is because the shorter wavelength of the radiation, the greater the increase in intensity at that wavelength. Therefore, the peak intensity is at a shorter wavelength than it was at the lower temperature.

Question 10

❌ How does a Constant Temperature affect Radiation

Answer 10

All bodies (objects), no matter what their temperature is, emit amd absorb radiation. A body at constant temperature emits infrared radition at the same rate as it absorbs it.

Also, an object that has a constant temperature emits radiation across a continuous range of wavelengths.

Question 11

❌ What Objects/Surfaces absorb infrared radiation, and an example of good infrared insulator?

Answer 11

Every object absorbs and emits infrared radiation, whatever it’s temperature is. If an object has a constant temperature, the object emits infrared radiation at the same rate as it absorbs it. When an object absorbs radiation faster than it emits radiation, it’s temperature increases.

Rescue teams use light-coloured blankets to keep accident survivors warm. A light, shiny outer surface emits a lot less radiation that a dark, matt surface. This keeps the patient warm, as less infrared radiation is emitted than if an ordinary blanket had been used.

Question 12

❌ How does the Atmosphere affect/change the Infraed Radiation’s affect on Earth (+ Factors to take into consideration)

Answer 12

The temperature of the Earth depends on lots of factors, such as the rate that light and infrared radiation from the Sun are:

• Refelected back into space or absorbed by the Earth’s atmosphere or by the Earth’ surface
• Emitted from the Earth’s surface and from the Earth’s atmosphere into space

If the Earth had no atmosphere, the temperature on the surface would plunge to aboute -180°C at night, the same as the Moon’s surface at night. This would happen because the surface would not be recieving any radiation from the Sun - it would be emitting radiation into space.

Some gases in the atmosphere, such as water vapour, methane, and carbon dioxide (greenhouse gases) absorb longer wavelength infrared radiation from the Earth and prevent it escaping into space. These gases absorb the radiation and then emit it back to the surface. This pricess makes the Earth warmer than it would be if these gases were not in it’s atmosphere.

Question 13

🟢 What is the definition of Specifc Heat Capacity

Answer 13

Specifc Heat capacity is the amount of energy (in joules) needed to raised the temperature of each kg of the substance by 1°C.

Question 14

🟢🟠 What are the Equations for Specific Heat Capacity + For Power

Answer 14

Specifc Heat Capacity (J/kg °C) = Number of Joules of Heat / Number of kg x Change in Temperature

(SHC = Joules/Mass x Change in Temp)

(This also means)

Specifc Heat Capacity (J/kg °C) = Power x Time / Mass x Change in Temperature

Your given the equation Energy Transferred = Mass x SHC x Temperature Change

(ΔE = m x c x Δθ)

Question 15

🟢 How does the energy tansferred to a substance affect the thermal energy

Answer 15

The energy transferred to the substance increases the thermal energy store of the substance by an equal amount.

Question 16

🟢 What are Storage heaters and what do they do? (How do they use SHC)

Answer 16

A storage heater uses electricity at night (off-peak) to heat special bricks or concrete blocks in the heater. Energy transfer from the bricks keeps the room warm. The bricks have a high specific heat capacity, so they can store lots of energy. They warm up slowly when the heater element is on, and cool down slowly when it is off.

Question 17

🟢 How can the rate of energy transfers in the home be reduced?

Answer 17

• Loft Insulation
• Cavity Wall Insulation
• Aluminium Foil between radiator panels
• Double-Glazed windows
• Thicker Layers of Brick With Lower Conductivity

Question 18

🟢 How can solar panels help heat the home?

Answer 18

Heating a home using electricty or gas can be expensive. Solar panels absorb infrared radiation from the Sun and are used to generate electricty directly (solar cell panels) or to heat water directly (solar heating panels). In the northern hemisphere, a solar oanel is usually fitted on a roof that faces south so that it absorbs as much infrared radiation from the Sun as possible.

Question 19

🟢 How can Loft Insulation help Insuate the home?

Answer 19

Loft insulation such as fibreglass reduces the rate of energy transfer through the roof. Fibreglass is a good insulator. The air between the fibres also helps reduce the rate of energy transfer by conduction. Tne greater the number of layers of insulation, the thicker the insulation will be. So the rate of energy transfer through the roof will be less.

Question 20

🟢 How can Cavity Wall Insulation help Insuate the home?

Answer 20

Cavity wall insulation reduces the rate of energy transfer through the outer walls of the house. The cavity of an outer wall is the space between the two layers of brick that make up the wall. The insulation pumped into the cavity. It is a bettr insulator than the air it replaces. It traps the air in small pockets, reducing the rate of energy transfer by conduction.

Question 21

🟢 How can Aluminium Foil between radiator panels help Insuate the home?

Answer 21

Aluminium foil between a radiator panel and the wall reflects radiation away from the wall and so reduces the rate of energy transfer by radiation.

Question 22

🟢 How can Double-Glazed windows help Insuate the home?

Answer 22

Double-glazed windows have two glass panes with dry air or a vacuum between the panes. The thicker the glass and the lower its thermal comductivity is, the solwer the rate of energy through it by conduction will be. Dry air is a good insulator, so it reduces the rate of energy transfer by conduction. A vacuum also prevents energy transfer by convection.

Question 23

🟢 How can Thicker Layers of Brick with lower conductivity help Insuate the home?

Answer 23

If the external walls of a warm building have thicker brickers and lower thermal conduxtivity, the rate of transfer of energy from the inside of the building to the outside will be lower and the cost of heating will be less.

Question 24

🟢🟠 What is the Equation for Power

Answer 24

Power = Current x Voltage