Physics · Science General

Heat Transfer Mechanisms

877 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

When heating up holiday leftovers in the microwave, what type of energy transformation occurs?

  1. thermal energy into electrical energy

  2. electromagnetic radiation into thermal energy

  3. electrical energy into electromagnetic radiation

  4. chemical energy into thermal energy
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Microwaves use electromagnetic radiation (microwaves) to excite water molecules in food, which increases their kinetic energy and manifests as thermal energy (heat).

Multiple choice

When potatoes are boiling to get softer for mashing, how does heat energy move?

  1. heat from the water transfers into the cold potatoes

  2. the cold from the potatoes transfers to the warm water

  3. heat from the water dissolved the cold potato molecules

  4. heat from the water evaporates cold potato molecules
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heat energy naturally flows from an area of higher temperature to an area of lower temperature. Therefore, heat moves from the hot water into the cooler potatoes.

Multiple choice thermo flask thermos flask heat energy transfers transfer of heat physics

A thermos flask is designed to prevent the contents of the flask from losing heat. Which of the following statements concerning the design of thermos flasks is incorrect?

  1. The stopper helps reduce heat loss by convection

  2. The glass walls are silver coated to reduce emitted radiation

  3. The flask is designed to prevent heat loss by conduction, convection and radiation

  4. The vacuum between the glass walls prevents heat loss by preventing radiation
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Yes, thermoflask is designed to prevent  the contents of the flask from losing heat.
The stopper, i.e. vacuum between double walls of thermoflask prevents heat transfer through convection.
The glass walls are silver coated because it reduces emitted radiation when they are silver coated i.e. made shiny. And we know that shiny surfaces reflects all the heat so all the heat is being reflected inside the walls and heat remains unaffected. And the thinesss of glass walls will stop heat entering or leaving the flask by conduction.
So, the flask is designed to prevent heat loss by conduction, convection and radiation.
Multiple choice thermo flask thermos flask heat energy transfers transfer of heat physics

Vacuum in a vacuum flask prevents heat transfer through process of-

  1. Conduction only

  2. Conduction and Convection

  3. Convection only

  4. Radiation only
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Vacuum in a vacuum flask prevents heat transfer through process of conduction and convection.
It is so because, in conduction there needs a direct contact for transfer of heat and there is vaccum between two layers, so conduction can't  transfer heat in this case. And in convection, heat is transferred by molecular motion in fluid (liquid or gas). But due to vaccum's presence between two layers, molecular motion is not possible So convection is also impossible for this case.
Multiple choice thermo flask thermos flask heat energy transfers transfer of heat physics

The silver coating on the inner bottle of a thermos flask

  1. prevents heat transfer by conduction

  2. prevents heat transfer by convection

  3. prevents heat transfer by radiation

  4. prevents heat transfer by absorption
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Due to the silver coating on the inner bottle, a shiny surface is formed. And these shiny surface act as a good reflector of heat 
As a result, they prevent the transfer of heat by radiation.
Multiple choice thermo flask thermos flask heat energy transfers transfer of heat physics

The walls of thermo-flask are polished because

  1. shining bodies are good absorber of heat

  2. shining bodies are good radiator of heat

  3. shining bodies have emisivity as one

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The wall of thermoflask are polished because shiny surface are good radiators of heat. Since we intend to keep in the vacuum flask and not have it radiated, Outside the shiny surface is best option. A black wall is bad option as they are good emitter and absorber of heat radiation.

Multiple choice thermo flask thermos flask heat energy transfers transfer of heat physics

The vacuum between the walls of the flask prevents the transfer of heat by

  1. Conduction

  2. Convection

  3. Radiation

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

Thermos flask is a special kind of bottle used for keeping the hot liquid hot and the cold liquid cool for a sufficiently long time. It was deviced by sir James Dewar and do it is also known as Dewar Flask. The vacuum between the walls of the flask prevents the transfer of  heat by conduction.

Multiple choice thermo flask thermos flask heat energy transfers transfer of heat physics

A polished silver surface is

  1. good absorber of heat

  2. good reflector of heat

  3. poor reflector of heat

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Heat rays are electromagnetic rays. Light rays are also electromagnetic rays. We know that a polished silver surface is a good reflector of light. this means that it is a good reflector of electromagnetic rays. Hence it is a good reflector of heat

Multiple choice thermo flask thermos flask heat energy transfers transfer of heat physics

A thermos flask maintains temperature of objects. It

  1. containing some kind of heating element to keep hot things hot.

  2. containing some kind of heating element to keep cold things cold.

  3. keeps hot things hot by not allowing heat to escape.

  4. All of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
A thermos flask maintains temperature of objects. It keeps hot things hot by not allowing heat to escape.
Thermos flask doesn't allow heat to escape from it via any mode of heat transfer i.e. conduction, convection, radiation. It does so by silver coating or polishing inner surface thin walls and vacuum between two walls.