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Physics Case study (4 Marks)

Laws of Thermodynamics · Uttarakhand Board (UBSE) STD 12 Science (Uttarakhand - English Medium). 4 questions.

Questions

Case study (4 Marks)

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4 questions · self-marked practice — reveal the answer and mark yourself.

Question 14 Marks
When we rub our hands they become warm. Have we supplied heat to the hands?
Answer
When we rub our hands, they become warm. In this process, heat is supplied to the hands due to the friction between the hands.
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Question 24 Marks
A closed bottle contains some liquid. The bottle is shaken vigorously for 5 minutes. It is found that the temperature of the liquid is increased. Is heat transferred to the liquid? Is work done on the liquid? Neglect expansion on heating.
Answer
A closed bottle containing some liquid is shaken vigorously such that work is done on the bottle (against the viscous force). Hence, the temperature of the liquid increases. However, no external heat is supplied to the system.
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Question 34 Marks
An ideal gas is pumped into a rigid container having diathermic walls so that the temperature remains constant. In a certain time interval, the pressure in the container is doubled. Is the internal energy of the contents of the container also doubled in the interval?
Answer
An ideal gas is continuously being pumped into the container. Therefore, the number of moles, n are continuously increasing. In a certain interval,
Pressure, $P_2 = 2P_1$
$n_2 = 2n_1$​​​​​​​
Thus, internal energy, $U = nC_vT$ will double as the number of moles get doubled.
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Question 44 Marks
When a tyre bursts, the air coming out is cooler than the surrounding air. Explain.
Answer
When a tyre bursts, adiabatic expansion of air takes place. The pressure inside the tyre is greater than the atmospheric pressure of the surrounding due to which the expansion of air occurs with some work done against the surrounding leading to decrease in the internal energy of the air present inside the tyre. This decrease of internal energy leads to fall in temperature of the inside air. Hence, the air coming out is cooler than that of the surrounding.
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