Which of the following represents a relation for 'heat lost = heat gained'?
- A.Principle of thermal equilibrium
- B.Principle of colors
- C.Principle of calorimetry
- D.Principle of vaporization
Correct answer
Explanation
The correct answer is C, Principle of calorimetry. It states that when hot and cold bodies are mixed in an insulated system, heat lost by the hot body equals heat gained by the cold body.
The principle follows from the law of conservation of energy, provided no heat escapes to the surroundings. It is used with the relation Q = m × s × ΔT, where m is mass, s is specific heat and ΔT is the change in temperature. By measuring the final temperature of a mixture, one can find the specific heat of a solid or the latent heat of melting ice. The instrument used for such measurements is a calorimeter, usually an insulated copper vessel.
A is wrong because thermal equilibrium (the zeroth law) says bodies in contact reach the same temperature; it defines temperature but does not state the heat balance. B is wrong because there is no such principle about heat; colours relate to light. D is wrong because vaporization is a change of state from liquid to gas, not a heat-balance law.
Exam tip: Calorimetry = heat lost = heat gained, using Q = msΔT; it rests on conservation of energy.
Practice Questions
View allWhich one of the following features is an indication for modification of stem of a plant?
- A.Presence of 'eye' on potato
- B.'Scale' found in onion
- C.'Tendril' found in pea
- D.'Hair' present in carrot
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The eyes of a potato are nodes with buds, and only a stem bears nodes and buds, so they prove that the potato is a modified stem.
Read the full explanation →Which one of the following metals is used in the filaments of photo-electric cells that convert light energy into electric energy ?
- A.Tungsten
- B.Copper
- C.Rubidium
- D.Aluminium
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Rubidium, an alkali metal like caesium, gives off electrons easily when light falls on it, so it is used in photoelectric cells.
Read the full explanation →Tooth enamel is made up of which one of the following calcium compounds ?
- A.Calcium carbonate
- B.Calcium sulphate
- C.Calcium hydroxide
- D.Calcium phosphate
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Tooth enamel is made mainly of calcium phosphate in the form of a hard crystal called hydroxyapatite. Enamel is the hardest substance in the human body, harder even than bone.
Read the full explanation →Which one of the following viruses used to be responsible for highly infectious disease Smallpox ?
- A.Adenovirus
- B.Variola virus
- C.Aichi virus
- D.Coxsackie virus
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Smallpox was caused by the variola virus, a large DNA virus of the pox family that spread from person to person through the air.
Read the full explanation →After fertilization, the fruit and the seed are produced by
- A.ovule and ovary, respectively
- B.ovary and ovule, respectively
- C.ovary, no ovule required
- D.ovule, no ovary required
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After fertilisation the ovary of the flower grows into the fruit, and each ovule inside it develops into a seed.
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