energy transfer by heating

thermal conductors

substances that conduct thermal energy very well. e.g. metal

thermal insulators

substances that do not conduct thermal energy very well. e.g. fibreglass and wool

the rate of thermal energy transfer depends on

• the temperature difference across the material

• the thickness of the material

• the thermal conductivity of the material

how to reduce the rate of thermal energy transfer

• increase the thickness

• have low thermal conductivity

infrared waves

Wavelengths that are long can be detected as heat. The sun gives off infrared waves with shorter wavelengths.

what happens if the object is hotter

more infrared radiation it emits

object that is constant temperature

emits infrared radiation at the same rate as it absorbs

black body radiation

the radiation emitted by a perfect black body (a body that absorbs all the radiation that hits it)

what happens if the temperature of an object increases

it absorbs more radiation than it emits

what happens if the object decreases

it absorbs less infrared radiation at a lesser rate than it emits

how is the earths temperature effected

emitting and absorbing infrared radiation of the sun and infrared radiation from the earth surface and atmosphere

specific heat capacity

the energy required to raise the temperature of one kg of a substance by one degree Celsius

how to find specific heat capacity

use an joulemeter and a thermometer it measure the initial and the final temperature

specific heat capacity equation

q=mc∆T

rearranging specific heat capacity equation to make it the subject?

c= energy (J) / mass (kg or G) x temperature change

How are houses heated?

electric or gas heaters, oil or gas central heating systems, or by solid fuel in stoves or in fireplaces

How can the rate of energy transfer from houses be reduced?

loft insulation

Cavity wall insulation

Insulation material that is used to fill the cavity between the two brick layers of an external house wall

aluminium foil in home

behind radiators and reflects infrared radiation back into the room

double glazing

reduces the rate of energy transfer through the windows

thick bricks

• thick bricks with a low thermal conductivity reduce the rate of energy transfer through exterior walls

solar panels

a panel designed to absorb the sun's rays as a source of energy for generating electricity or heating.

conduction

The direct transfer of heat from one substance to another substance that it is touching.

why metals are better conductors than non- metals

metals have free electrons to move and carry quickly through the lattice

convection

The transfer of heat by the movement of a fluid

examples of convection

boiling water, hot air balloon rising

radiation

The transfer of energy by electromagnetic waves

Why does metal feel colder than wood at the same temperature?

Metal is a better conductor, so it transfers heat away from your skin faster, making it feel colder.

Describe the required practical for insulation.

Measure cooling of hot water in containers with different insulating materials. Control variables: volume of water, container, starting temperature.