P2 Energy transfer by conduction Flashcards
What are thermal conductors?
Thermal conductors are materials that allow thermal energy to move through them easily
What materials are good thermal conductors?
Metals
What are thermal insulators?
Thermal insulators are materials that don’t allow thermal energy to move through them easily
What materials are good thermal insulators and why?
Fibreglass and wool are good thermal insulators as they trap air making it harder for thermal energy to be transferred through them
What factors does the rate of thermal transfer through a material depend on? (3 things)
The difference in temperature across the material
The thickness of the material
The thermal conductivity of the material
How can you reduce the rate of thermal energy transfer?
Using a insulating material that is as thick as possible and has a low thermal conductivity as possible
How can you reduce unwanted energy transfers of heat?
By using thermal insulation to reduce energy waste as heat
The insulator should be as thick as possible and have as low a thermal conductivity as possible
What happens to the temperature of an object when you heat it and why?
When an object is heated its temperature increases as energy is transferred into it
What is the specific heat capacity of an object?
the specific heat capacity is the amount of energy needed to change the temperature of 1kg of the substance by 1°C
What does it mean if an object has a greater specific heat capacity?
The greater the specific heat capacity of a substance the more energy is needed to increase its temperature by 1°C
It also means the temperature of the object increases more slowly
What does it mean if an object has a greater mass?
The greater the mass of a substance the more energy is needed to increase its temperature by 1°C
It also means the temperature of the object increases more slowly
How can you work out the change in energy needed to increase the temperature of a substance by a set amount?
ΔE = m x c x Δθ
Where:
ΔE = Change in energy measured in J
m = mass measured in kg
c = specific heat capacity of the substance in J/kg°C
Δθ = Change in temperature measured in °C
What is specific heat capacity measured in?
Joules per kilogram, celcius
J / kg°C
How can the equation be rearranged to work out the specific heat capacity of a given substance?
C = (ΔE) ÷ (m x Δθ)
Where:
ΔE = Change in energy measured in J
m = mass measured in kg
c = specific heat capacity of the substance in J/kg°C
Δθ = Change in temperature measured in °C
How are houses heated?
By using electric or gas heaters
Oil or gas central heating systems
Solid fuel in stoves or fireplaces
How can you reduce fuel bills for heating your house?
Reducing the rate of energy transfer out of the house
How can you reduce rate of energy transfer out the house? (5 ways)
Fibreglass loft insulation
Cavity wall insulation
Aluminium foil behind the radiators
Double glazed windows
Thick bricks with low thermal conductivity
How does fibreglass loft insulation
reduce energy transfer out of the house?
Fibreglass loft insulation reduces rate of energy transfer through the roof
What is cavity wall insulation and how does this reduce energy transfer out of the house?
Cavity wall insulation is when there is two layers of bricks with a layer of insulating material inbetween
This reduces the rate of energy transfer through the outer walls of the house
How does aluminium foil behind the radiators reduce energy transfer out of the house?
This reflects infrared radiation (heat) from the radiators back into the room reducing how much is lost
How does double glazing reduce energy transfer out of the house?
Double glazing increases the thickness of the windows and reduces the rate of energy transfer through the windows
How does using thick bricks with low thermal conductivity reduce energy transfer out of the house?
Using thick bricks with low thermal conductivity reduces the rate of energy transfer through the exterior walls
How does the rate of cooling of a building depend on the thickness and thermal conductivity of its walls?
The THICKER and HIGHER the thermal conductivity a house’s walls the LONGER it takes to cool down
The THINNER and LOWER the thermal conductivity of a house’s walls the QUICKER it cools down
What are the different parts of a solar panel and what do they do?
Solar cell panels - Absorb infrared radiation from the sun to directly generate electricity
Solar heating panels - Absorb infrared radiation from the sun to heat water directly
