Heat questions | form five Physics

Mention three qualities that make a particular property suitable for use in a practical
thermometer.

Study the values in Table 1 which represent the observations of a particular room temperature obtained by using two types of thermometers and then answer the questions that follow:

Table 1

Temperature in	Resistance measured by resistance thermometer ()	Pressure recorded by constant volume gas thermometer(Nm-2)
Sterm point, 100°C	75,000	1.10×10​7
Ice point, 0°​ C	63,000	8.00×106
Unknown room temperature	64,992	8.51×10​6

(i)Calculate the value of unknown room temperature on the scales of resistance  thermometer and constant volume gas thermometer.
(ii) Why do the answers in (i) above differ slightly?

Define coefficient of thermal conductivity.

Write down two characteristics of a perfectly lagged bar.

A thin copper wall of a hot water tank having a total surface area of 5.0m​² contains 0.8m​³ of water at 350K and is lagged with a 50mm thick layer of a material of thermal  conductivity 4.0×10​^-2​Wm^-1​ K^-1​. If the thickness of copper wall is neglected and the temperature of the outside surface is 290K,
(i) Calculate the electrical power supplied to an immersion heater.
(ii) If the heater were switched off, how long would it take for the temperature of hot water to fall by 1K?

The element of an electric fire with an output of 1000​Watts is a cylinder of 250mm long and 15​mm ​ in diameter. If it behaves as a black body, estimate its temperature.

Give two ways in which the internal energy of the system can be changed.

List down two simple applications of the First law of thermodynamics in our daily life.

One mole of a gas expands from volume, V_​1 to a volume V​_2​ . If the gas obeys the
Van-der-Waal`s equation; , derive the formula for work done in this process.

A heat engine works at two temperatures of 27°C and 227°C. Calculate the:
(i) Efficiency of the engine.
(ii) Temperature which will increase the efficiency by 10% if the room temperature is kept at 27°C.