Which of these is the SI unit for energy?

• A watt
• B pascal
• C newton
• D joule

A user operates a hand-cranked dynamo torch.

Use words from the box below to complete the sentences. Each word may be used once, more than once, or not at all.

• The hand-cranked dynamo converts ____________ energy into ____________ energy.
• The LED bulb converts this energy into useful ____________ energy and wasted ____________ energy.

The diagram below shows the Sankey energy diagram for this LED bulb.

Draw on this

Calculate the amount of thermal energy wasted by the LED bulb.

State the equation linking efficiency, useful energy output, and total energy input.

Calculate the efficiency of the LED bulb.