Q: The process in which rate of transfer of heat is maximum is :

\$\textbf{Step 1}\$: There are three modes of transmission of heat. They are Conduction, convection and radiation. Conduction: In this mode of transmission. heat dissipates from one place to another by molecular vibration. It is relevant to solid only. Conduction needs a medium to transfer heat. Convection: Heat is transferred from one place to another by the transfer of molecules. It happens only in liquids or gases. It also needs a medium to transfer heat. Radiation: It transfers heat in the form of electromagnetic waves. It can heat any form of material. It doesn't need any medium for the transfer of heat. \$\textbf{Step 2}\$: We know that radiation travels with the speed of light. So, the rate of heat transfer is maximum in radiation in the form of electromagnetic radiation. Thus option C is correct.

Q: The temperature at which a body does not radiate energy

Energy radiated becomes \$0\$ only when absolute temperature becomes \$0\$.

Question 1

Sunlight contains ultraviolet radiations which makes it feel hot.

Accepted Answer

Sunlight consists of many wavelengths.The longer wavelengths from the sun causes heat by vibrating electrons in the substances that absorbs these wavelengths light. Thus, the infrared radiation is responsible for warming the earth's surface. Infrared light is reflected more than ultraviolet or visible light due to its longer wavelengths.Hence above statement is false.

Question 2

Assertion (A): When hot water is poured in a thick glass tumbler then the tumbler breaks.Reason (R): Glass is a bad conductor of heat

Accepted Answer

When hot water is poured into a thick tumbler its inner surface expands. However, Since glass is bad conductor of heat  , the heat does not go to outer surface and the expansion of outer surface of the tumbler is quite small. Due to uneven expansion of the outer and inner surfaces, the tumbler breaks. because the heat will try to escape but the glass would not allow it and in the process ultimately glass breaks down.

Question 3

By which of the following methods could a cup of hot tea lose heat when placed on metallic table in a class rooma) conduction b) convectionc) radiation d) evaporation of liquid.

Accepted Answer

Conduction occurs through the walls of the cup.Radiation occurs from the top surface.Convection occurs at the top of the cup.Evaporation of liquid also occurs.

Question 4

The lowest attainable fahrenheit temperature is

Accepted Answer

The lowest possible temperature, or absolute zero as it is called is $-459.4^{o} F$.  By international agreement, absolute zero is taken as &#8722;273.15 degrees on the Celsius scale (International System of Units), which equals $-459.4^{o} F$ degrees on the Fahrenheit scaleHence, option B is correct.

Question 5

Statement-1Radiation involves transfer of heat by electromagnetic waves.Statement-2Electromagnetic waves do not required any material medium for propagation.

Accepted Answer

Electromagnetic waves are formed due to simultaneous oscillations in electric and magnetic field (both are perpendicular to each other and perpendicular to the propagation of the em wave). Both electric and magnetic fields can exist in a vacuum and do not need a material medium to exist or oscillate. So an electromagnetic wave can propagate without a medium.These radiations carry energy with them, so when a body releases radiation it loses energy, which manifests into a temperature loss. When radiation (energy) is absorbed, the body gains energy which is manifested in the form of a temperature gain. This is basically a heat transfer with radiation.Both statement 1 and Statement 2 are true, but Statement-2 is not the correct explanation for Staement-1.Option B is correct.

Question 6

For an ideal conductor, thermal resistance is :

Accepted Answer

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Question 7

The process in which rate of transfer of heat is maximum is :

Accepted Answer

$\textbf{Step 1}$: There are three modes of transmission of heat. They are Conduction, convection and radiation. Conduction: In this mode of transmission. heat dissipates from one place to another by molecular vibration. It is relevant to solid only. Conduction needs a medium to transfer heat. Convection: Heat is transferred from one place to another by the transfer of molecules. It happens only in liquids or gases. It also needs a medium to transfer heat. Radiation: It transfers heat in the form of electromagnetic waves. It can heat any form of material. It doesn't need any medium for the transfer of heat. $\textbf{Step 2}$: We know that radiation travels with the speed of light. So, the rate of heat transfer is maximum in radiation in the form of electromagnetic radiation. Thus option C is correct.

Question 8

Which of the follwing is the smallest rise in temperature?

Accepted Answer

There are 180 divisions in the Fahrenheit scale between the ice point and steam point while there are only 100 divisions in a Celsius scale.And one scale division of a Kelvin scale is same as that of a Celsius scale.So, $1^0F$ indicates a smaller rise in temperature than $1^0C$ and $1K$.

Question 9

If we place our hand below a lighted electric bulb. We feel warmer because of :

Accepted Answer

There are three ways by which heat transfers:Conduction: for which the two bodies need to be in contactConvection: for which there needs to be a material medium between the two bodiesRadiation: which occurs if there is a temperature difference, irrespective of whether there is a material medium or not.In this case, there is a medium between the two. But the two bodies are not in contact. Hence, there is radiation and convection which matches with option D.

Question 10

The temperature at which a body does not radiate energy

Accepted Answer

Energy radiated becomes $0$ only when absolute temperature becomes $0$.

Heat

Physics
3515 Views

Sunlight contains ultraviolet radiations which makes it feel hot.

Assertion (A): When hot water is poured in a thick glass tumbler then the tumbler breaks.
Reason (R): Glass is a bad conductor of heat

By which of the following methods could a cup of hot tea lose heat when placed on metallic table in a class room
a) conduction
b) convection
c) radiation
d) evaporation of liquid.

The lowest attainable fahrenheit temperature is

Statement-1
Radiation involves transfer of heat by electromagnetic waves.
Statement-2
Electromagnetic waves do not required any material medium for propagation.

For an ideal conductor, thermal resistance is :

The process in which rate of transfer of heat is maximum is :

Which of the follwing is the smallest rise in temperature?

If we place our hand below a lighted electric bulb. We feel warmer because of :

The temperature at which a body does not radiate energy

Heat

Physics 3515 Views

Sunlight contains ultraviolet radiations which makes it feel hot.

Assertion (A): When hot water is poured in a thick glass tumbler then the tumbler breaks. Reason (R): Glass is a bad conductor of heat

By which of the following methods could a cup of hot tea lose heat when placed on metallic table in a class room a) conduction b) convection c) radiation d) evaporation of liquid.

The lowest attainable fahrenheit temperature is

Statement-1 Radiation involves transfer of heat by electromagnetic waves. Statement-2 Electromagnetic waves do not required any material medium for propagation.

For an ideal conductor, thermal resistance is :

The process in which rate of transfer of heat is maximum is :

Which of the follwing is the smallest rise in temperature?

If we place our hand below a lighted electric bulb. We feel warmer because of :

The temperature at which a body does not radiate energy

Physics
3515 Views

Assertion (A): When hot water is poured in a thick glass tumbler then the tumbler breaks.
Reason (R): Glass is a bad conductor of heat

By which of the following methods could a cup of hot tea lose heat when placed on metallic table in a class room
a) conduction
b) convection
c) radiation
d) evaporation of liquid.

Statement-1
Radiation involves transfer of heat by electromagnetic waves.
Statement-2
Electromagnetic waves do not required any material medium for propagation.