Physics · Oct / Nov 2020 · Paper 41 · Question 4
0625
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A large test-tube contains a liquid at room temperature. An electric heater is immersed in the liquid and is switched on. Thermal energy is supplied to the liquid by the heater. The temperature of the liquid increases until it reaches its boiling point. The liquid then starts to change into gas.
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4(a)[3]
molecules close(r)
molecules move only small distances (between collisions) or do not move freely
molecules move in clusters or slide past each other
4(b)[2]
molecules (in liquid) move faster or gain energy
molecules move apart (on average)
4(c)(i)[1]
molecules overcome forces / gain potential energy as the liquid boils
4(c)(ii)[3]
(m =) ρV (in any form) or 0.86 × 50 or 43 (g)
(lv =) Q ÷ m (in any form) or 18 000 / 43 or 18 000 / (0.86 × 50)
420 J / g or 4.2 × 105 J / kg
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