Which of the following changes would reduce the rate of unwanted thermal energy transfer from a hot water tank to its surroundings?
Painting the tank's outer surface with a dull black finish
Adding a layer of thermal insulation around the tank
Decreasing the thickness of the tank's walls
Increasing the temperature of the water inside the tank
37 exam-style questions on OCR GCSE Physics Power and efficiency. Each one has a worked solution and a mark scheme showing where the marks go.