Explain that electrical energy is dissipated as thermal energy in the…

The idea

When charge flows through a component that has resistance, the supply's electrical energy is transferred to the component and then spreads to the surroundings as thermal energy. The current does work against the resistance, so the component and the air around it warm up and the energy becomes less useful for further electrical work. A filament lamp is the standard example: electrons are pushed through the filament, the filament becomes hot and glows, and heat passes to the surrounding air by conduction, convection and radiation. The same idea explains why cables and resistors warm up. Energy is conserved overall, but it is dissipated, meaning it spreads into the environment at low temperature and is no longer easily harnessed.

What earns the marks

• States that electrical energy is transferred to thermal energy in the surroundings when current flows through resistance.
• Identifies the surroundings or environment as the place where the dissipated thermal energy ends up.
• Explains that the current does work against the resistance of the component.
• Recognises that energy is conserved but becomes spread out and less useful after dissipation.
• Applies the idea to a named example such as a filament lamp or a resistor heating up.

Common mistakes and how to put them right

• Claims that energy is destroyed when a component heats up.

  Put it right: State that energy is conserved and transferred to the surroundings as thermal energy.

• Says the current is used up as it passes through a resistor.

  Put it right: Explain that charge is conserved and it is energy that is transferred.

• Describes the component cooling the surroundings.

  Put it right: State that the component transfers thermal energy to the surroundings and warms them.

• Treats dissipation as a loss of energy from the universe.

  Put it right: Explain that the energy spreads out and becomes less useful, not that it vanishes.

Exam tips

• Link the answer explicitly to resistance: without resistance there is no heating effect to describe.
• Name where the thermal energy goes, using the word surroundings rather than leaving it vague.
• Use a concrete component such as a filament lamp to show the transfer from electrical to thermal energy.
• Avoid saying energy is lost; use dissipated and explain that it spreads into the environment.