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Heat Questions - GCSE Level

Q13. A heater uses energy from a laptop computer to keep a mug of coffee hot. The diagram shows the heater connected to a laptop computer.

(a) Give two factors, other than the material of the mug, that would affect the rate of energy transfer to the coffee.

Any two factors:

surface area (of mug in contact with cup warmer)

thickness of mug

temperature of heater / coffee or temperature difference (between heater and coffee)

power of the heater/laptop

[2 marks]

(b) Energy is conducted slowly through the base of the glass mug. Explain how energy is conducted through the base of the glass mug.

As atoms/molecules/particles in the glass gain kinetic energy they vibrate faster/with greater amplitude

If you say 'start to vibrate' you get no marks - the vibration of particles is present in all particles, even at very low temperatures - when they get hotter the vibrational energy increases - it does not 'start'.

That energy/those vibrations are passed on from particle to neighbouring particle by collision.

An answer in terms of free electrons scores zero - glass has no free electrons.

[2 marks]

(c) Energy is transferred to the coffee at the bottom of the mug. Explain how a convection current is set up in the coffee.

The particles near to the heat source gain energy and spread out (the warm liquid expands) making the heated coffee in that region become less dense. The less dense fluid rises and is relaced by falling cooler/denser coffee which in turn is heated, thus setting up a convection current.

[4 marks]

(8 marks total)