Convection

Q. Adhesion enables us to write on blackboard with chalk.

1. False
2. True

Q. Convection coefficient depends upon

1. $\text{Density}$
2. $\text{Specific heat}$
3. $\text{Thermal conductivity}$
4. $\text{All the above}$

Q. Which of the following curves shows correct relation between convective resistance $\left(R\right)$ and radius of hot sphere $\left(r\right)$ being placed in a stream of cold air ?

1. 
2. 
3. 
4. 

Q. According to Newton's law of cooling, if the body is much hotter than its surrounding, then it will cool down quickly.

1. True
2. False

Q.

Assuming Newton's law of cooling to be valid, the time taken by a body to cool from a temperature $T_1$ to a temperature $T_2$ in a room where the temperature is $T_0$ $(T_0<T_2<T_1)$ is proportional to

1. $lo{g}_e\left(\frac{T_1-T_0}{T_2-T_0}\right)$

2. $lo{g}_e\left(\frac{T_2-T_0}{T_1+T_0}\right)$

3. $lo{g}_e\left(\frac{T_1-T_2}{T_0}\right)$

4. $lo{g}_e\left(\frac{T_1+T_0}{T_2+T_0}\right)$

Q. It is hotter for the same distance over the top of the fire than it is by the side is mainly because

1. air conducts heat upward.
2. heat is radiated upward.
3. convection takes more heat upwards.
4. convection, conduction and radiation all, contribute significantly in transferring heat

Q. In which of the following processes, convection does not take place primarily?

1. Sea and Land breeze
2. Boiling of water
3. Heating air around a furnace
4. Warming of glass of bulb due to filament

Q. A solid sphere of radius $4\text{cm}$ and a hollow sphere of same material and having outer radius $4\text{cm}$ and inner radius $2\text{cm}$ are heated to the same temperature and allowed to cool in the same room. The ratio of the rate of fall of temperatures is

1. $7:8$
2. $8:5$
3. $2:1$
4. $4:1$

Q.

How does the fan help us in keeping cool?

1. Decreasing the temperature of the air in the room.

2. Increasing the rate of natural convection.

3. Increasing the rate of forced convection.

4. Increasing the rate of conduction.