Question

10 (a) (i) state two applications of thermal expansion and contraction. 2
(ii) with the aid of a diagram, explain how a thermostat in an electric iron works. 4
(b) (i) state any three physical properties which vary with temperature. 3
(ii) suggest, with a reason, a suitable thermometer for measuring temperature 1. in a blast furnace, 2. in a deep freezer. 4
(c) (i) define boyles law. 1
(ii) suggest and give an explanation for the following: 1. it takes two hours to cook meat but if sodium carbonate is added it will take less time. 2. water will take long to boil when heated in an open pot. 4
(iii) a certain quantity of gas at constant temperature has a volume of 30.0 cm³ at a pressure of 1.01 x 10⁵ pa. determine its volume when the pressure is 2.01 x 10⁵pa. 2

Explanation:

(a)(i)

Thermal expansion and contraction are used in:

1. Thermometers - Liquid expands/contracts with temperature change to show temperature.
2. Gaps in railway tracks - Allow for expansion in hot weather to prevent buckling.

(a)(ii)

A thermostat in an electric iron has a bimetallic strip.

1. As the iron heats up, the bimetallic strip (made of two different metals with different expansion rates) bends due to differential expansion.
2. When it bends enough, it breaks the electrical contact, turning off the heating element. When the iron cools, the strip returns to its original shape, reconnecting the circuit and turning the heating - element back on. A simple diagram would show the bimetallic strip, electrical contacts, and the heating element.

(b)(i)

Three physical properties that vary with temperature are:

1. Volume of a liquid (e.g., mercury in a thermometer expands with increasing temperature).
2. Electrical resistance of a metal (resistance of most metals increases with temperature).
3. Density of a gas (density of a gas decreases as temperature increases at constant pressure).

(b)(ii)

1. For a blast furnace (high - temperature environment, up to 1500 - 1600°C), a thermocouple thermometer is suitable. Reason: It can measure high temperatures accurately and has a fast response time.
2. For a deep - freezer (low - temperature environment, around - 20°C), an alcohol thermometer is suitable. Reason: Alcohol has a low freezing point (- 114°C) and can measure low temperatures without freezing.

(c)(i)

Boyle's law states that for a given mass of gas at constant temperature, the pressure of the gas is inversely proportional to its volume, i.e., \(P_1V_1 = P_2V_2\).

(c)(ii)

1. When sodium carbonate is added to meat while cooking, it increases the boiling point of water. This is because the solute (sodium carbonate) elevates the boiling point according to the colligative property of boiling - point elevation. Higher boiling point means water is at a higher temperature, and heat transfer to the meat is faster, reducing the cooking time.
2. Water takes long to boil in an open pot because heat is lost to the surroundings. Some of the heat energy is used to warm the air around the pot, and evaporation also occurs from the surface of the water, taking away heat. So, more heat is required to reach the boiling point.

(c)(iii)

1. Given \(P_1 = 1.01\times10^{5}\text{ Pa}\), \(V_1 = 30.0\text{ cm}^3\), \(P_2 = 2.01\times10^{5}\text{ Pa}\).

• According to Boyle's law \(P_1V_1 = P_2V_2\).
• We can solve for \(V_2\): \(V_2=\frac{P_1V_1}{P_2}\).
• Substitute the values: \(V_2=\frac{1.01\times 10^{5}\text{ Pa}\times30.0\text{ cm}^3}{2.01\times 10^{5}\text{ Pa}}\approx15.0\text{ cm}^3\).

Answer:

(a)(i) Thermometers, Gaps in railway tracks.
(a)(ii) See above explanation with diagram concept.
(b)(i) Volume of a liquid, Electrical resistance of a metal, Density of a gas.
(b)(ii) 1. Thermocouple thermometer, for high - temperature measurement. 2. Alcohol thermometer, for low - temperature measurement without freezing.
(c)(i) For a given mass of gas at constant temperature, pressure is inversely proportional to volume (\(P_1V_1 = P_2V_2\)).
(c)(ii) 1. Sodium carbonate elevates boiling point, so meat cooks faster. 2. Heat is lost to surroundings and evaporation occurs, so water takes long to boil in an open pot.
(c)(iii) \(15.0\text{ cm}^3\)