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1. Q15(a) — What is thermal equilibrium? State Zeroth Law of Thermodynamics.
Answer:
Thermal equilibrium is the state in which two bodies in contact have the same temperature and there is no net flow of heat between them.
Zeroth Law: If two bodies are separately in thermal equilibrium with a third body, then they are in thermal equilibrium with each other.
2. Q15(b) — If change in temperature is 45°C, what is the change in Fahrenheit scale?
Answer:
\Delta F=\frac{9}{5}\Delta C
\Delta F=\frac{9}{5}\times45
\boxed{\Delta F=81^\circ F}
Answer: 81°F
3. Q16(a) — Why do objects expand on heating?
Answer:
When a body is heated, its particles gain kinetic energy and vibrate more vigorously. The average distance between the particles increases, causing the body to expand.
4. Q16(b) — Why are gaps left between railway tracks?
Answer:
Gaps are left between railway tracks to allow thermal expansion. During hot weather, the tracks expand. The gaps prevent the tracks from bending or buckling.
5. Q17(a) — State the principle of calorimetry.
Answer:
The principle of calorimetry states that:
Heat lost by the hot body = Heat gained by the cold body, provided there is no heat loss to the surroundings.
6. Q17(a) — Why is a calorimeter made of copper?
Answer:
A calorimeter is made of copper because copper has low specific heat capacity and good thermal conductivity. Therefore, it quickly reaches the temperature of the contents and absorbs relatively little heat.
7. Q17(a) — Why is the calorimeter polished from inside?
Answer:
The inside of a calorimeter is polished to reduce heat loss by radiation.
8. Q17(b) — Define heat capacity and water equivalent.
Heat capacity:
The amount of heat required to raise the temperature of a body by 1°C (or 1 K).
C=\frac{Q}{\Delta T}
Water equivalent:
The mass of water that has the same heat capacity as the given body.
9. Q17(c) — Why does temperature remain constant during a phase change?
Answer:
During a phase change, the heat supplied is used to change the state of the substance rather than increase its temperature. Therefore, the temperature remains constant until the phase change is complete.
10. Q17(d) — How does pressure affect the melting point and boiling point of water?
Answer:
Increasing pressure lowers the melting point of ice.
Increasing pressure raises the boiling point of water.
11. Q20(a) — Explain quantization of charge.
Answer:
Quantization of charge means that electric charge exists only in integral multiples of the elementary charge.
q=ne
where n is an integer and
e=1.6\times10^{-19}C
12. Q20(b) — What is electrostatic shielding?
Answer:
Electrostatic shielding is the process of protecting a region from an external electric field by surrounding it with a conducting material.
Example: Cars and metal enclosures can provide electrostatic shielding.
13. Q20(c) — Why do bodies get electrified when rubbed together?
Answer:
When two different materials are rubbed together, electrons are transferred from one body to the other. One body becomes positively charged and the other becomes negatively charged