P2 + P6

What is thermal conductivity?

What the energy transfer by conduction through a material depends on.

Low thermal conductivity = ?

= good insulator

What does energy transfer depend on?

- The temperature difference across the material

- The thickness of the material

- The thermal conductivity of the material

How do you reduce the energy transfer as much as possible?

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 practically possible

What material are the best conductors of energy?

Metals

What materials are the best insulators?

Non-metal materials e.g. wood and fiberglass are the best insulators

The higher the thermal conductivity of the material...

...the higher the rate of energy transfer through it.

The thicker a layer of insulating material...

...the lower the rate of energy transfer through it.

What is loft insulation made of and why is it a good insulator?

It is made of fibre glass - reduces the rate of energy transfer through the roof. The air between the fibreglass helps reduce heat loss through conduction.

Where is cavity wall insulation and how is it a good insulator?

It is on the outer walls. Insulation in the cavity traps the air in small pockets which reduces conduction.

Where is aluminium foil based and how does it work?

It is between a radiator panel and the foil reflects radiation away from the wall.

What are double glazed windows and how does it reduce the transfer of energy?

It is 2 glass panes with dry air/a vacuum between the panes. - The thicker glass reduces the thermal conductivity (slower rate of transfer)

- The dry air reduces conduction

- The vacuum reduces convection

How does thicker bricks reduce thermal conductivity?

As the bricks are thick, there is a longer path for heat to travel through.

How do solar panels work and where are they placed?

They absorb infrared radiation from the Sun. Solar cell panels - generate electricity while solar heating panels - heats water directly. In the northern hemisphere solar panels face south.

What things are used to heat houses?

Electric/gas heaters, gas/oil-fired central heating, solid-fuel stores are used to heat houses.

What is cavity wall insulation?

It is an insulation material that is used to fill the cavity between the 2 brick layers of an external wall.

What does specific heat capacity tell us? What are the units

It tells us how much energy is required to change the temperature of 1kg of a substance by 1°C. Unit - J/kg °C

What is the equation for energy transferred for change in temperature?

Energy Transferred = mass (kg) x specific heat capacity (J/kg°C) x change in temp. (°C)

What is the equation for energy transferred (change in temp.) in symbols?

E = mc∆theter

What does a high specific heat capacity mean?

It means you need a high amount of energy to heat it

Better conductors means...?

low specific heat capacity

What is density?

It is mass per unit volume

What is the equation for density

Density (kg/m³) = mass (kg) / volume (m³)

How do you find the density for a regular cuboid?

Weigh mass with a top pan balance

Measure L, W and H and calculate volume

Substitute values into the density equation to find density

How do you find the density of an irregular shape using a measuring cylinder?

Measure the mass with a top pan balance

Measure starting amount of water in measuring cylinder (ml)

Place object in and measure the water level now

Calculate the displacement (which is the volume) (end-start)

Substitute values into density equation

How do you measure the density of an irregular shape using a eureka can

Measure the mass of the irregular shape using a top pan balance

Fill up the eureka can above the spout hole and let it run.

Once it water stops coming out of the spout, place the irregular shape into the eureka can with a measuring cylinder underneath the spout

Once the water has stopped running out of the spout, measure the water in the measuring cylinder using the measuring cylinder. This is the volume

Input the values into the density equation​

What is internal energy?

the sum of the kinetic and potential energies of all of the particles that compose the system

What are the kinetic and potential energies?

K - motion relative to each other P - positions relative to each other

What is the name for a change from solid --> gas?

Sublimation

What is the name for a change from gas --> solid

Deposition

What is specific latent heat?

The energy transferred when a substance changes state (per kg for specific)

Specific latent heat equation?

E (joules) / m (kg)

What is specific latent heat of fusion?

Change of state between solid and liquid

What is specific latent heat of vaporisation?

Change of state between liquid and gas

Pressure compared to temperature?

P directly proportional to T

Temperature compared to volume?

Volume directly proportional to T

Volume compared to Pressure?

P is inversely proportional to volume

Electromagnetic Spectrum?

visible light, radio waves, microwaves, infrared radiation, ultraviolet, x rays, gamma rays

What is a perfect black body?

An object that absorbs all radiation that hits it, doesn't reflect/transmit any radiation - good emitter = good absorber