Edexcel - London Examinations GCE, January 1999 - Paper 2 Question 2

2. a) (i) Infra-red radiation energy from the sun. This infra-red radiation has a very short wavelength and it can penetrate the glass easily on reaching the greenhouse. However, when the objects inside are heat up by absorbing the infra-red energy, they emit their own infra-red waves of a longer wavelength which are unable to penetrate the glass and escape; so they are trapped inside. Therefore the air inside starts heating up and the temperature rises. This is called the 'greenhouse effect'.

(ii) Hot air therefore rises up by convection and it escapes through the vent. Hence the temperature inside stops increasing. (10 marks)

b) See graph below:

At night, no infra-red energy is absorbed from the sun, so the temperature falls by normal losses of energy e.g. conduction through the glass (from hot air inside to cold air outside). The air temperature becomes steady when it reaches the temperature of the air outside, as there is no further loss of energy then. (10 marks)