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GCSE Questions - Electromagnetic Spectrum

Q3.

 

The diagram above shows a way that biscuit manufacturers can cook large quantities of biscuits.

The uncooked biscuits are placed on a moving metal grid. The biscuits pass between two hot electrical heating elements inside an oven. The biscuits turn brown as they cook.

The oven has two control knobs, as shown in in the diagram below.

 

 

(a) Which type of electromagnetic radiation makes the biscuits turn brown? [1 mark]

infra-red radiation

(b) Suggest two ways of cooking the biscuits in this oven, to make them turn browner.

To turn browner they need to absorb more infra-red radiation. Therefore you could either pass them through the heating elements at a slower speed (by turning the speed control knob to a lower speed setting)or increase the power to the heating elements (by turning the power knob to a higher setting). This would make them hotter and give off more infra-red energy which would be absorbed by the biscuits.

You could also pass the biscuits through a second time. [2 marks maximum]

(c) The inside and outside surfaces of the oven are light-coloured and shiny. Explain why.

Note that the question mentions the inside AND outside surfaces. This is a clue that the examiners want you to mention both of them in your answer!

Infra-red radiation ( take care not to say 'light' - we are dealing with infra-red here!) is reflected by shiny surfaces. The radiation given off from the heating elements would therefore be reflected back ( never say 'bounce back' instead of reflect - examiners don't like it!) from the inside of the oven towards the bicuits, increasing the efficiency of the oven.The outside surface being shiny reduces the loss of energy from the oven, as shiny surfaces are poor emitters of radiation.

[3 marks maximum]

(Total 6 marks)