Allow students to try out the devices, and either have them try and figure out how they make heat themselves, or discuss as a group.
Note: probably do not run several hair dryers/space heaters at once or they will trip school electrical fuses.
The space heater, hair dryer, kettle and incandescent light bulb make heat from electricity:
The electrical energy is converted to heat energy by the device, by running a current through a metal coil or plate to heat it up.
In the space heater and hair dryer, the hot metal warms air, then the hot air is blown out with a fan.
The metal coil inside the kettle is heated by electricity, which heats the water above it.
The incandescent light bulb is designed to produce light, and works when electricity passes through a thin wire inside the bulb. The wire heats up an emits light, but also a lot of heat. Incandescent bulbs are not efficient for their purpose as only 5% of the energy emitted is as light - the rest is heat, hence the the conversion to other kinds of light bulbs (fluorescent, now LED).
The candle and hand warmer make heat from chemistry:
The candle gives off heat as the wax burns (a chemical reaction - see candle chemistry activity. A candle is used for light, and also for heat sometimes.
The hand warmer works as sodium acetate crystallizes (turns from a liquid solution to a solid). It is in solution until the metal disc is bent, which initiates the crystallization. You can then see the crystal formation spreading out from the metal disc. Crystallization of this chemical produces heat. (You can reset the hand warmer by heating it up to dissolve the sodium acetate in the water again.) Hence chemical energy is converted to heat energy in these hand warmers.
Other discussion points:
Our bodies make heat from chemical energy.
Rubbing your hands together makes heat from friction.
We heat our homes by burning gas (a chemical reaction that makes heat, similar to the candle), or from electricity (heating up metal inside a device, similar to the space heater and hair dryer).
Geothermal energy is an environmentally sound way of heating buildings - heat is extracted from deep underground and used to directly heat buildings, or used to heat up water that can be used for heating. Thousands of buildings in Richmond, BC are heated in this way.
