Heating effect of electric current

The idea

Part of a source's energy may do useful work while the rest heats the gadget; in a purely resistive circuit the source energy is entirely dissipated as heat, which is the heating effect of electric current.

A warm fan

An electric fan has been running for hours in a room, and its body has become warm. A cell or battery is the source of the energy it uses.

What has happened to part of the energy that the source supplied?

• It was spent as heat, which warmed the fan
• It was stored in the room as electrons
• It disappeared completely

Where the energy goes

Press Next step to follow the energy of a source.

Heat from current

Some of the energy does useful work and the rest is spent as heat. In a circuit that has only resistors, all of it ends up as heat. That is the heating effect of electric current.

Part of a source's energy may do useful work, while the rest heats the gadget. In a purely resistive circuit the source energy is entirely dissipated as heat, which is the heating effect of electric current.

Notes

Part of a source's energy may do useful work and the rest heats the gadget; in a purely resistive circuit it is entirely dissipated as heat: the heating effect of electric current.

Check yourself

In a purely resistive circuit, what happens to the source energy?

Why does an electric fan become warm after running for a long time?

What is meant by a purely resistive circuit?

Which of these devices uses the heating effect of electric current?

• All of it does useful work. In a purely resistive circuit, that is, resistors only joined to a battery, the source energy is dissipated entirely as heat.
• Half is stored and half is used. The source energy is dissipated entirely in the form of heat in a purely resistive circuit.
• It is entirely dissipated as heat — correct. Yes!
• Part of the source energy is spent as heat instead of rotating the blades — correct. Yes!
• The fan makes new heat from nothing. The heat comes from the energy that the source supplies. A part of that energy does useful work, and the rest goes to heat the gadget.
• All the source energy does useful work. Only a part does useful work, such as rotating the blades. The rest is expended as heat.
• A circuit with a fan in it. A fan turns some of the energy into useful work, so a circuit with a fan is not purely resistive.
• A circuit of resistors only, connected to a battery — correct. Yes!
• A circuit with no battery. A battery is needed. A purely resistive circuit is a configuration of resistors only connected to a battery.
• An ammeter. An ammeter measures current. An electric heater and an electric iron are the devices based on the heating effect.
• A switch. A switch makes or breaks a conducting link. An electric heater and an electric iron are the devices based on the heating effect.
• An electric heater — correct. Yes!