K.C.S.E Physics Q & A - MODEL 2012PP1QN17

K.C.S.E Physics Q & A - MODEL 2012PP1QN17

(a) Figure 11 shows how an underground room was ventilated. It had two vents, one at A and the other at B. A fire was lit at point C.​

​Explain what happened to the ventilation when the fire was lit. 
(b) Explain how a vacuum flask minimizes loss of heat through radiation. 
(c) In an experiment to investigate the unusual expansion of water, a fixed mass of water at O°C was heated until its temperature reached 20°C. On the axis provided, sketch a graph of density against temperature of the water from O °C to 20°C. 

(d) An immersion heater rated 2.5 kW is immersed into a plastic jug containing 2 kg of water and switched on for 4 minutes. Determine;
(i) the quantity of heat gained by the water;
(ii) the temperature change for the water;
(take specific heat capacity of water as 42 x 10³Jkg^-1K^-1).

ANSWERS

​(a)  Fire heats air around region C which expands and becomes less dense;
 The less dense air rises up the vent and emerges at A;
 Cool (more dense) air moves down the vent at B introducing fresh air into the mine 
(b) The flask has double walls which are silverly on both sides the shiny surface is a good reflector of heat;