STUDY QUESTIONS
1. (a) Define heat energy and its units
(b) Name four effects which the heat energy can
bring about in a material body
2. What do you understand by the term "change of
state"?
3. Define the following
(a) Fusion
(b) Fusion point
(c) Solidification
(d) Solidification point
4. (a) How do the fusion point and solidification
point of ice and water compare numerically?
(b) Describe different sources of heat energy
5. Define the following:
(a) Vaporisation
(b) Vaporisation point
Answers
:) Answer (:
1. (a) Heat is a form of internal energy which flows from a hot body to a cold body when they are kept in contact. The S.I unit of heat is joule ( symbol J ). The other most commonly used unit of heat is calorie ( symbol cal ).
(b) The four effects which the heat energy can bring about in a material body are: (i) Change in Temperature, (ii) Change in Dimensions, (iii) Change in State.
2. Change of a substance from one physical state to another state is called change of state. As matter can exist in three physical states viz: Solid, liquid and vapour. For example. water can exist in three different physical states: Solid( Ice ), liquid( water ) and Gas( water vapour ). Solid to gas : Sublimation , Solid to liquid : Melting , Liquid to gas : Evaporation , Liquid to solid : Freezing , Gas to solid : Deposition , Gas to liquid : Condensation.
3. (a) the heat absorbed by a unit mass of a given solid at its melting point that completely converts the solid to a liquid at the same temperature: equal to the heat of solidification. (Or) In simple definition, The change from solid to liquid phase by the absorption of heat at a constant temperature is called melting( fusion ).
(b) The constant temperature at which a solid changes to liquid is called fusion point.
(c) Solidification, also known as freezing, is a phase change of matter that results in the production of a solid. Generally, this occurs when the temperature of a liquid is lowered below its freezing point.
(d) Freezing point, temperature at which a liquid becomes a solid.
4. (a) The melting and freezing point of water is the same '0' degree Celsius. Suppose if water is in the solid state, ie., ice at '0′ , then only on supply of 80 calories of heat per gram to the solid ice, it will be converted into liquid water. Only for this change in state of ice to water the above heat energy is required.
(b) The sources of heat energy are: Sun, Earth, Wood, Fossil Fuels and Nuclear particles.
5. (a) The change from liquid to gas phase on absorption of heat at a constant temperature, is called vaporization( boiling ).
(b) The particular temperature at which vaporization occurs is called the vaporization point.
