Physics · Science General

Heat Transfer Mechanisms

828 Questions

Heat Transfer Mechanisms deal with the movement of thermal energy through conduction, convection, and radiation. It involves practical applications like ocean heat storage and atmospheric heating. These fundamental physics concepts are frequently asked in general science sections.

Thermal conductionHeat convectionThermal radiationSpecific heatStates of matter

Heat Transfer Mechanisms Questions

Multiple choice

As the temperature increases, the thermal conductivity of a gas

  1. Increases

  2. Decreases

  3. Remains constant

  4. Increases up to a certain temperature and then decreases
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Correct option is (1). The kinematic theory of gases predicts & the experiment confirms that the thermal conductivity of gases is proportional to the square root of thermodynamic temperature. thermal conductivity of gases$\alpha$ $(temperature)^{\frac{1}{2}}$ as temp  $\uparrow$        Conductivity of gas $\uparrow$

Multiple choice

Biot number signifies the ratio of

  1. convective resistance in the fluid to conductive resistance in the solid

  2. conductive resistance in the solid to convective resistance in the fluid

  3. inertia force to viscous force in the fluid

  4. buoyancy force to viscous force in the fluid
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Multiple choice

Consider a two-dimensional laminar flow over a long cylinder as shown in the figure below.

The free stream velocity is $U\omega$ and the free stream temperature $T\omega$ is lower than the cylinder surface temperature Ts. The local heat transfer coefficient is minimum at point

  1. 1

  2. 2

  3. 3

  4. 4
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In laminar flow, the heat transfer coefficient is minimum where the thickness of boundry layer is maximum. The heat transfer coefficient is maximum where the thickness is minimum. For turbulent-region thickness of boundry layer is maximum at 3. For laminar region thickness of boundry layer is maximum at 2 so it will have minimum local heat transfer coefficient.

Multiple choice

Heat and work are

  1. intensive properties

  2. extensive properties

  3. point functions

  4. path functions
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Multiple choice

The ratios of the laminar hydrodynamic boundary layer thickness to thermal boundary layer thickness of flows of two fluids P and Q on a flat plate are $\frac{1}{2}$ and 2 respectively. The Reynolds number based on the plate length for both the flows is 104. The Prandtl and Nusselt numbers for P are $\frac{1}{8}$ and 35 respectively. The Prandtl and Nusselt numbers for Q are respectively

  1. 8 and 140

  2. 8 and 70

  3. 4 and 70

  4. 4 and 35
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Multiple choice physics electric current and its effects coil and fuse heating effect of electric current- uses applications of heating effect of electric current

From below which are the applications of heating effect of electric current?

  1. Electric immersion water heater

  2. Electric Iron Box

  3. Electric Fuse

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

According to heating effect of electric current, heat is produced in the materials that have resistance, thus electric immersion water heater, electric iron box and electric fuse are the applications of heating effect of electric current.

Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

The molecules of medium vibrate about their mean positions during heat transfer in the process of

  1. Conduction

  2. Radiation

  3. Convection

  4. None
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The molecules of medium transfer heat as they vibrate about mean position in conduction.
The molecules of medium absorb heat, they rise and other molecules of medium come to take their place convection
In radiation, medium does not play role.

Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

Air is a bad conductor of heat because:

  1. it's molecules are in continuous contact with each other.

  2. it's molecules are not in continuous contact with each other

  3. it's molecules absorb all the heat

  4. it's molecules are moving randomly due to Brownian motion
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Air is a bad conductor of heat because it's molecules are not in continuous contact with each other.
Air molecules are too far to disperse heat energy to one another efficiently. Heat is conducted by molecules and atoms that are very closely bonded together and vibrating at high frequency.
Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

.................. surface absorbs more heat than any other surface under identical conditions.

  1. White & Shiny

  2. White & Rough

  3. Black & Rough

  4. Yellow & Shiny
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Black & rough surface absorbs more heat than any other surface under identical conditions.
Black surface absorbs all the radiations more easily than any surface as its absorptivity is $1$.
Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

The heat transfer in air is poor because

  1. it take place mainly due to convection

  2. it take place mainly due to conduction

  3. it take place mainly due to radiation

  4. all of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Air is a gas and its molecules are far apart from each other. So, this is not a good condition for conduction. Also, air being a non-metal doesn't have free electrons for conduction. Hence option B is not applicable.

C is also not applicable because radiation doesn't need any medium. Air being a fluid, convection can take place through it. But convection is not a very fast mode of transfer of heat.

Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

How does air trapped by the woolen fabric help ?

  1. Air is a good conductor of heat and allows warm air to come near body

  2. Air is a bad conductor of heat and allows body heat to escape into atmosphere

  3. Air is a bad conductor of heat and doesn't allow body heat to escape into atmosphere

  4. Air is a good conductor of heat and doesn't allow cool air to come near body.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Air trapped by the woolen fabric help us during winter. As air is bad conductor of heat and doesn't allow body heat to escape into atmosphere. The heat stored inside the body does not goes out as wool and air acts as a layer of insulator. And body heat is not escaped from the body.

Multiple choice evs - i transfer of heat clothes - our necessity applications of insulation uses of good and poor conductors in daily life voyages and discoveries applications of heat conduction

A shining metallic ball with a small black spot on its surface is heated to very high temperature and then quickly taken to a dark room. Then.

  1. Both appear equally bright

  2. The spot appears brighter than the ball

  3. The spot appears darker than the ball

  4. Both are invisible in the dark room
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to Kirchhoff's law of radiation, good absorbers are good emitters. A black spot is a better absorber than the shiny surface, so it will emit more radiation and appear brighter when the object cools in a dark room.