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Miracle Learning Centre Science Tuition Question on Thermal Energy (O Level Science Tuition/IP Science Tuition/Secondary Science Tuition)

1) The figure below shows two identical glass cylinders containing equal volumes of water, initially at room temperature. Identical electric heaters were placed in the cylinders, near the top in cylinder A and near the bottom in cylinder B.

The heaters were switched on at the same time. The readings of the thermometers then changed as shown in the figure below.

a) Explain how heat is spread in a liquid by convection. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________

b) On the figure above, label A or B to indicate the heating curves for the corresponding cylinders. Explain why one cylinder has a slower rate of increase in temperature than the other. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________

2) A baby’s milk bottle containing some milk is heated in a bottle warmer. The bottle warmer has foam filled walls and a shiny outer casing as shown.

The warmer is heated by a 100 W heating element. The heating element raises the temperature of the water in the warmer to 40°C. (a) State the difference between the terms ‘thermal energy’ and ‘temperature’. …………………………………………………………………………………….. …………………………………………………………………………………..

(b) Explain why the rate of thermal energy loss from the bottle warmer can be reduced by (i) the foam filled walls, and ……………………………………………………………………………… (ii) the shiny casing. ………………………………………………………………………………

(c) The warmer contains 0.50 kg of water at a temperature of 25°C. The warmer is set to switch off when the water reaches 40°C. When there is no bottle in the warmer, calculate the time taken to raise the temperature of the water to 40°C. (specific heat capacity of water = 4200 J/(kg°C)) time taken = ……………………..

(d) Give a reason why the water will take a longer time to heat up in reality compared to the answer you obtained in (c). …………………………………………………………………………………….. …………………………………………………………………………………..

Miracle Learning Centre Answer to Science Tuition Question on Thermal Energy. (O Level Science Tuition/IP Science Tuition/Secondary Science Tuition) 1. a) When a liquid is heated, it expands and its density decreases. Hence, it floats up and colder liquid, which is denser, sinks to take its place, thus forming convection currents. b) A has the gentler curve. The temperature of A increases slowly as the heat from the heater can only reach the bottom of the container by conduction. As liquids are poor conductors of heat, the temperature of A increases slowly.

2) A baby’s milk bottle containing some milk is heated in a bottle warmer. The bottle warmer has foam filled walls and a shiny outer casing as shown.

The warmer is heated by a 100 W heating element. The heating element raises the temperature of the water in the warmer to 40°C.

(a) State the difference between the terms ‘thermal energy’ and ‘temperature’. Temperature is a measure of degree of hotness of a body. Thermal energy of a body represents the total kinetic energy of the atoms or molecules in the body.

(b) Explain why the rate of thermal energy loss from the bottle warmer can be reduced by (i) the foam filled walls, and Foam contains trapped air and air is a poor conductor of heat. (ii) the shiny casing. Shiny surfaces are poor emitters of radiant heat.

(c) The warmer contains 0.50 kg of water at a temperature of 25°C. The warmer is set to switch off when the water reaches 40°C. When there is no bottle in the warmer, calculate the time taken to raise the temperature of the water to 40°C. (specific heat capacity of water = 4200 J/(kg°C)) time taken = …………………….. (d) Give a reason why the water will take a longer time to heat up in reality compared to the answer you obtained in (c). There is some heat loss to the surroundings by convection. Learn from our Science Tuition Questions and Answers. Miracle Learning Centre Call 6463 8756 or sms 8128 8342/9839 9908. (Specialist in Science and Maths) for Primary, Secondary and JC levels. Miracle Learning Centre specialises in Science tuition, Maths tuition, Chemistry tuition and Physics tuition classes.