Tag: temperature and heat

Questions Related to temperature and heat

SI units of thermal conductivity are

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. W/m - K.

  2. W/m

  3. W/K

  4. None

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Correct Option: A
Explanation:

From the formula:

Rate of heat flow $= \dfrac{(k \times A \times (Change\ of\ temp))}{Thickness}$
Units of $k$ are $W/m-K$.

The thermal conductivity of a rod depends on

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. length

  2. mas

  3. area of cross section

  4. material of the rod

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Correct Option: D

Coefficient of thermal conductivity :

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. depends upon nature of the material of the body

  2. is independent of dimensions of the body

  3. both 1 and 2

  4. only 1

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Correct Option: A
Explanation:

Coefficient of thermal conductivity of a rod is an intrinsic property. It depends on the material of the rod and not on the dimensions of the rod.

A red hot brick is placed on an iron tripod stand which stands on a large block of copper. The brick loses heat by:

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. conduction

  2. conduction and radiation

  3. conduction and convection

  4. conduction, convection, and radiation

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Correct Option: B
Explanation:

The brick loses heat (i) by conduction through iron tripod stand to the copper block which is then radiated away and convection currents are set up in the surrounding air, and (ii) by radiation.

A constant voltage is applied between the two ends of a uniform metallic wire. Some heat is
developed in it. The heat developed is doubled if

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. both the length and the radius of the wire are halved.

  2. both the length and the radius of the wire are doubled

  3. the radius of the wire is doubled

  4. the length of the wire is doubled

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Correct Option: B

In the Arctic region hemispherical houses called Igloos are made of ice. It is possible to maintain a temperature inside an Igloo as high as $20^o$C because.

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. Ice has high thermal conductivity

  2. Ice has low thermal conductivity

  3. Ice has high specific heat

  4. Ice has higher density than water

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Correct Option: B
Explanation:

ice is good at trapping heat. It is a  good insulator and low thermal conductivity .

A long silver tea spoon is placed in a cup filled with hot tea. After some time, the exposed end (the end which is not dipped in tea) of the spoon becomes hot even without a direct contact with the tea. This phenomenon can be explained mainly by_______

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. conduction

  2. reflection

  3. radiation

  4. thermal expansion

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Correct Option: A
Explanation:

As atoms in the spoon vibrates about their equilibrium positions and transfer energy form one end to other end. This process is called conduction.

A piece of metal is heated to increase its temperature from $5^{\circ}C$ to $15^{\circ}C$. The increase in temperature expressed in $K$ and $^{\circ}F$ are respectively.

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. $10\ K, 18^{\circ}F$

  2. $283\ K, 50^{\circ}F$

  3. $18\ K, 10^{\circ}F$

  4. $50\ K, 283^{\circ}F$

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Correct Option: A
Explanation:

$K=273.16+C\F=\cfrac{9C}{5}+32\quad dK=dC \quad dF=\cfrac{9}{5}dC$

A/Q, $dC=15-5=10\ \therefore dK=10K,\quad dF=\cfrac{9}{5}\times10=18°F$

A slab of stone area $3500{cm}^{2}$ and thickness $10cm$ is exposed on the lower surface to steam at ${100}^{o}C$. A block of ice at ${0}^{o}C$ rests on upper surface of the slab. In one hour $4.8kg$ of ice of melted. The thermal conductivity of the stone is $J{s}^{-1}$ ${m}^{-1}$ ${k} _{-1}$ is
(Latent heat of ice $=3.36\times { 10 }^{5 }J/kg$)

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. $12.0$

  2. $10.5$

  3. $1.02$

  4. $1.24$

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Correct Option: D
Explanation:

Given :  $A = 3500 \ cm^2 = 0.35 \ m^2$         $l = 10 \ cm = 0.1 \ m$             $\Delta T =100-0 = 100^o C$
Mass of ice melted  $m = 4.8 \ kg$
Time taken  $t = 1 \ hr = 3600 \ s$
Latent heat of ice  $L = 3.36\times 10^{5} \ J/kg$
Heat absorbed by ice = Heat conducted by slab
$\therefore$   $mL = \dfrac{KA t\Delta T}{l}$
Or    $4.8\times 3.36\times 10^{5} = \dfrac{K(0.35) (3600)(100)}{0.1}$
$\implies \ K = 1.24 \ Js^{-1} m^{-2} k^{-1}$

Which of the following minimizes the transference of heat in a thermos flask?
$1$. Conduction
$2$. Convection
$3$. Radiation

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. $2$ and $3$

  2. $1$ and $2$

  3. $1, 2$ and $3$

  4. $1$ and $3$

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Correct Option: C