 # Physics Practical Class 11 To study the relationship between the temperature of a hot body and time by plotting a cooling curve. Viva Questions with Answers

1) Which is the fastest mode of heat transfer?

Radiation is the quickest mode of heat transfer because it travels at the speed of light. The slowest mode of heat transmission is conduction because it takes place from particle to particle.

2) Name the law that governs the phenomenon of thermal radiation.

Stefan-Boltzmann Law rules the phenomenon of thermal radiation. This law states that the fourth power of the absolute temperature of a surface is proportional to the total radiant heat power emitted from that surface.

3) Thermal energy is converted to which form of energy in thermal radiation?

Due to the thermal motion of the particles in the substance, the thermal energy is converted to electromagnetic energy. A substance emits thermal radiation if its temperature is more significant than absolute zero. The motion of the particles causes the acceleration of charge, and hence electromagnetic energy is produced due to the dipole oscillation of these accelerating charges.

4) Can you prevent radiation using a good insulator?

Yes, we can prevent heat radiation using shiny or reflective material that reflects heat from the radiation from inside and outside material or object. For example, a thermos bottle is coated with shiny material and a lining to prevent heat conduction.

## 5) What is Newton’s Law of Cooling?

The difference in the body’s temperature and its surroundings is directly proportional to the rate of heat loss from a body. This is known as Newton’s law of cooling.

6) We can use Newton’s law of cooling on a body that is kept in a room containing air at 30°C, and the body’s temperature is 300°C. Is it true or false?

The given statement is false because Newton’s law of cooling can only be applicable when there is a small temperature difference.

7) What is heat transfer?

To study the transmission of energy from a high-temperature reservoir to a low-temperature reservoir, the phenomenon of heat transfer was introduced from the branch of thermal engineering.

8) According to which law the transfer of heat takes place?

According to the second law of thermodynamics, the thermal energy per unit temperature that is inaccessible for doing useful work (the total entropy of an isolated system) can never decrease. Hence, the second law of thermodynamics explains the heat transfer process.

9) The amount of heat received by the body when heat is radiated from a hot source, depends on the nature of the body. Is it true or false?

Yes, it is true because radiation is the phenomenon in which heat transmission takes place by electromagnetic waves. For example, a black body, as compared to any other body, will absorb more energy from the same source.

10) Using which phenomenon, the walls inside deep freezers absorb heat from food materials and keep them cool.

The walls absorb heat by radiation inside deep freezers from food materials and keep them cool.