1. Differentiate between the caloric and kinetic theories of heat as they existed in the eighteenth century. (4 marks)
2. Discuss the role of Joule’s experiments in establishing the principle of conservation of energy (2 marks)
3. Define Temperature. (1 mark)
4. Draw and explain the design of:
(a) laboratory thermometer; (b) clinical thermometer (c) thermocouple
(9 marks)
5. Explain thermal expansion (2 marks)
6. Explain the following gas laws:
• Boyle’s Law
• Charles’ Law
• Pressure Law
• General Gas Law (8 marks)
7. Distinguish between specific heat capacity, ‘c’ and heat capacity ‘C.
(2 marks)
8. Define specific latent heat capacity. (2 mark)
9. Distinguish between evaporation and boiling. (4 marks)
10. Explain the transfer of thermal energy by Conduction, Convection and radiation. (6 marks)
Answers
Answer:
1. CALORIC THEORY The caloric theory of heat is an
obsolete theory from the 18th
century.
•Heat was believed to be an invisible
fluid called ‘caloric’, which could
combine with matter and raise its
temperature.ARGUMENTS FOR THE CALORIC
THEORY
1.Objects expand when heated because
the increased ‘caloric’ they contain
causes them to occupy more space.
2.Heat flows from hotter to cooler
bodies because ‘caloric’ particles
repel each other.ARGUMENTS AGAINST THE
CALORIC THEORY
1. When bodies are heated so that they change state (solid to
liquid or liquid to gas), an increase in ‘caloric’ cannot be
detected.
2.When different materials are given the same amount of
heat (‘caloric’), their temperatures increase by different
amounts, indicating that they receive different quantities
of ‘caloric’.
3.The weight of a body should increase as it is heated,
because it should then contain more ‘caloric’. However, the
weight remains the same.RUMFORD’S CANNON-BORING
EXPERIMENT AS EVIDENCE AGAINST
CALORIC THEORY
• Count Rumford was an army officer responsible for
the boring of cannons during the late 18th century.
• He realised that the heat energy transferred when
a cannon was being bored was inexhaustible and
depended only on the work done in boring the hole.
• The ‘caloric’ theory was therefore not possible; if
‘caloric’ was a material substance, there would be a
time when all of it had left the cannon.KINECTIC THEORY
• The kinetic theory of matter states the following.
• The particles of matter (atoms, molecules) are in constant motion. The
kinetic energy they possess is responsible for their temperature, or
hotness.
• There is space between particles. Forces (bonds) pull them together when
they are near to each other, and so the particles have potential energy.
• When a substance is heated, the heat energy supplied could result in an
increase in the kinetic energy of the particles of the substance, and
hence in its thermal energy, causing the temperature to rise.
• When a substance is heated so that it changes state, the heat energy
supplied results in an increase in the spacing of the particles and hence
an increase in their potential energy, allow them to break bonds with
their neighbours and to expand against any surrounding pressure.
Answer:
1. A hot object contained a large quantity of caloric while a cold object contained very little of no caloric. Heat was transferred from one place to another via the movement of caloric. In 1798 Benjamin Thompson also known as Count Rumford proposed the kinetic theory of heat. ... The procedure produced a lot of heat energy.
2. Joule's paddle-wheel experiment [4] is the most famous of his conservation-of-energy experiments because, as we now know, it gave the most accurate results for the mechanical equivalent of heat. The experiment was performed in the cellar of Joule's house and was simplicity in itself (see figs.
3. Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of energy, when a body is in contact with another that is colder or hotter. Temperature is measured with a thermometer.
4. a. Laboratory thermometers are designed small to make it potable. Bulb of laboratory thermometer is usually larger than its bore in order to contain more liquid, to improve its sensitivity. That's why its more precise as even a small change in temperature will make the liquid to rise in the capillary tube.
b. Design of the clinical thermometer: Here we discuss a clinical thermometer which comprises of a glass tube with the scale inscribed on it as shown in Figure 1. One of the tube ends is filled with liquid mercury which is of red colour. An extremely thin capillary tube runs through the middle of the glass tube.
c. A typical circuit diagram of a thermocouple is shown in Figure. In the Figure, two dissimilar metals 'A' and 'B' are joined at the two junctions 'P' and 'Q'. Here the 'P' junction is measuring junction or hot junction whereas the junction 'Q' is the reference junction or cold junction.
5. Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic energy of a substance.
6. a. Boyle's law—named for Robert Boyle—states that, at constant temperature, the pressure P of a gas varies inversely with its volume V, or PV = k, where k is a constant. ... Charles (1746–1823)—states that, at constant pressure, the volume V of a gas is directly proportional to its absolute (Kelvin) temperature T, or V/T = k.
b. Charles's law, a statement that the volume occupied by a fixed amount of gas is directly proportional to its absolute temperature, if the pressure remains constant. This empirical relation was first suggested by the French physicist J. See also perfect gas. ..
c. Gay-Lussac's law, Amontons' law or the pressure law was found by Joseph Louis Gay-Lussac in 1808. It states that, for a given mass and constant volume of an ideal gas, the pressure exerted on the sides of its container is directly proportional to its absolute temperature.
d. The combined gas law is also known as a general gas equation is obtained by combining three gas laws which include Charle's law, Boyle's Law and Gay-Lussac law. The law shows the relationship between temperature, volume and pressure for a fixed quantity of gas.
7. Two difference between Heat Capacity and Specific Heat Capacity are :
(1) : Heat Capacity of the substance is defined as the amount of heat required to raise the temperature of the substance by 1
o
C whereas Specific Heat Capacity is defined as the amount of heat required to raise the temperature by 1
o
C of unit mass of substance.
(2) : Specific Heat Capacity does not depend on mass of substance whereas Heat Capacity depends on mass of substance.
8. The specific latent heat of a substance is the amount of energy needed to change the state of 1 kg of the substance without changing its temperature.
9. Evaporation is a normal process that occurs when the liquid form changes into the gaseous form; while causing an increase in the pressure or temperature. Boiling is an unnatural process where the liquid gets heated up and vaporized due to continuous heating of the liquid
10. Conduction is the transfer of thermal energy through direct contact. Convection is the transfer of thermal energy through the movement of a liquid or gas. Radiation is the transfer of thermal energy through thermal emission.
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