12 13 Spacecraft in orbit will be exposed to ultraviolet radiation from the Sun. Due to the photoelectric effect they can become charged. (a) Scientists have observed that one such spacecraft becomes charged when the frequency of the radiation is greater than 9.9 × 1014 Hz. The table lists the work function of some metals. metal Work function eV aluminium 4.1 caesium 2.1 nickel 5.0 platinum 3.3 Deduce the metal that covers the outside of the spacecraft. 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Explain why the aeroplane charges at a slower rate than the spacecraft due to the photoelectric effect. 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(Total for Question 13 = 10 marks)