STRUCTURES

FUN IN SCIENCE

ECOSYSTEMS

SCIENCE

SCIENCE

Conduction , Convection and Radiation

Heat Transfer

Heat Transfer #2

Radiation

"How to toast bread!" When a piece of bread is put in a toaster the wires inside the toaster glow red hot on either side of the bread.

How does the heat energy get to the bread?

Is it by conduction?

No, the heat energy cannot conduct through the air to the bread because air is a very bad conductor.

Is it by convection?

No, hardly any of the heat energy could have travelled to the bread by convection, as the hot air particles would rise out of the toaster.

The heat energy must have reached the toast some other way. It travelled as radiated heat. This heat energy movement is sometimes called heat waves, but strictly speaking, it is infrared radiation.

Hot objects radiate heat to their colder surroundings. The weird thing is that the surface colour of an object makes a difference.

Black and dull surfaces emit (give out) and absorb radiation well.

White and shiny surfaces do not emit radiation well and reflect radiation instead of absorbing it.

HEAT

Science Notes
All particles have kinetic energy and thernal energy.

Kinetic energy is the energy of motion.

Thermal Energy is the kinetic energy and the energy of attraction of particles.

Temperature is a measurement  of the kinetic energy of all the particles of an object.

Gases are most easily compressed.

There is a lot of space between gas particles, but not a lot of space between particles in liquids or solids.

When a substance is cooled, the particles within the substance slow down . Slower particles travel shorter distances, so the volume  of  a substance decreases as it contracts.

As you cool or heat substance, the volume may change but not the size or mass of the particles.