(a)(i) Define dew point. (ii) Explain why dew forms more quickly on the metal parts than on the rubber parts of a bicycle placed in the open overnight. (b)(...
(a)(i) Define dew point. (ii) Explain why dew forms more quickly on the metal parts than on the rubber parts of a bicycle placed in the open overnight.
(b)(i) Explain the statement. the specific heat capacity of copper is 400 J/kg/K. (ii) Two metals, P and Q are supplied with the same quantity of heat.
If the ratio of the specific heat capacity of P to Q is 3 : 1 and their masses are in the ratio I:2 respectively.
calculate the ratio of the temperature rise of P to Q.
(c)(i) Define coefficient of thermal conductivity of a material.
(ii)
The diagram above illustrates a composite bar of iron and copper. The bar is insulated along its sides and it has a diameter of 10 mm. The length and thermal conductivity of the iron are 0.15 m and 40 W/m/K, respectively and those of copper are 0.05 m and 360 W/m/K, respectively. If the free ends of the iron and copper are kept at 100°C and 0°C respectively. calculate the (i) temperature at the interface between the bars; (ii) rate of heat flow along the bar.
(a)(i) Dew point
Dew point is the temperature at which the water vapour present in air is just sufficient to saturate the air, so that condensation begins to occur.
(a)(ii) Why dew forms faster on metal than on rubber
Metal is a better conductor of heat than rubber. At night, the metal parts of the bicycle lose heat more rapidly and become colder faster than the rubber parts. Their temperature therefore falls below the dew point earlier, causing water vapour in the surrounding air to condense as dew on the metal surfaces. Rubber is a poor conductor of heat, so it cools more slowly and dew forms on it later.
(b)(i) Meaning of the specific heat capacity of copper being 400 J kg-1 K-1
It means that 400 J of heat energy is required to raise the temperature of 1 kg of copper by 1 K (or 1°C).
(b)(ii) Ratio of temperature rise
For each metal,
\[Q = mc\Delta\theta\]
Since the same quantity of heat is supplied to both metals:
Dew point is the temperature at which the water vapour present in air is just sufficient to saturate the air, so that condensation begins to occur.
(a)(ii) Why dew forms faster on metal than on rubber
Metal is a better conductor of heat than rubber. At night, the metal parts of the bicycle lose heat more rapidly and become colder faster than the rubber parts. Their temperature therefore falls below the dew point earlier, causing water vapour in the surrounding air to condense as dew on the metal surfaces. Rubber is a poor conductor of heat, so it cools more slowly and dew forms on it later.
(b)(i) Meaning of the specific heat capacity of copper being 400 J kg-1 K-1
It means that 400 J of heat energy is required to raise the temperature of 1 kg of copper by 1 K (or 1°C).
(b)(ii) Ratio of temperature rise
For each metal,
\[Q = mc\Delta\theta\]
Since the same quantity of heat is supplied to both metals:
