Tag: physics

Questions Related to physics

For a constant power source across a resistor, heat generated in a resistor:

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. increases with increase in resistance

  2. increases with increase in applied potential

  3. increases with decrease in resistance

  4. is constant

Show answer
Correct Option: D
Explanation:

Heat generated across the resistor is given by

$Q=I^2Rt = VIt$
Since, power supplied is constant,
$VI = \text{constant}$
$\implies Q = constant$ 

How much heat, in joules, must be added to 0.250 mol of Ar(g) to raise its temperature from 20.0 to $36.0^\circ C$ of at constant pressure?

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. $50.0J$

  2. $83.14J$

  3. $18J$

  4. $200J$

Show answer
Correct Option: B
Explanation:

At constant pressure,
$q=nCp  \Delta t$               $C _p =\frac{5R}{2}$
$=(0.25) \left ( \frac{5}{2} \times 8.314  \right ) (16)$
$=83.14 J$

The $1847$ Joule's experiment was aimed at.

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. Determining the mechanical equivalent of heat

  2. Determining the temperature for the maximum density of water

  3. Investigating the heating effect of electric current

  4. Investigating the internal energy of a gas

Show answer
Correct Option: A

Heat produced by the resistance R is:

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. $\displaystyle \frac { VIt }{ 4.2 } $

  2. $\displaystyle \frac { W }{ J } $

  3. $\displaystyle \frac { { i }^{ 2 }Rt }{ 4.2 } $

  4. All

Show answer
Correct Option: D
Explanation:

From Joule's Law of heating-


Heat produced$=H=I^2Rt$

Now, $V=IR$

$\implies H=(IR)It=VIt$

And, $I=\dfrac{V}{R}$

$H=I^2Rt=\dfrac{V^2}{R^2}Rt=\dfrac{V^2}{R}t$

In which of the following process, convection does not takes place primarily?

physics transfer of heat applications of convection convection thermal energy transfers

  1. sea and land breeze

  2. Boiling of water

  3. warming of glass of bulb due to filament

  4. heating air around a furnace

Show answer
Correct Option: C
Explanation:
Heat transfer of glass bulb from filament is through radiation. 
A medium is required for convection process.
As a bulb is almost evacuated, heat from the filament is transmitted through radiation.

A double-plane window consist of two glass sheets each of area $1m^2$ and thickness $0.01m$ separated by a $0.05m$ thick stagnant air space In the steady state, the room glass interface and the glass outdoor interface are at constant temperature of $27^oC$ and $0^oC$ respectively. The rate of heat flow through the window plane is (Given , $k _{glass}=0.8\,\,W\,\,m^{-1}K^{-1},K _{air}=0.08\,\,W\,\,m^{-1}K^{-1})$

physics transfer of heat applications of convection convection thermal energy transfers

  1. $41.5\,\,W$

  2. $31.5\,\,W$

  3. $21.5\,\,W$

  4. $11.5\,\,W$

Show answer
Correct Option: A
Explanation:

Total thermal resistance is 
$R=\dfrac{t _1}{K _1A _1}+\dfrac{t _2}{K _2A _2}+\dfrac{t _1}{K _1A _1}$


$R=2\times \dfrac{0.01}{0.8\times 1}+\dfrac{0.05}{0.08\times 1}= 0.65W^{-1}K$

$\therefore $Heat current $,H=\dfrac{\triangle T}{R}=\dfrac{27-0}{0.65}=41.5W$

A 1200 kg car is braked to a stop from 100 km/h. If 60% of this energy appears in the steel brake drums, whose total mass is 10 kg its temperature will rise by $\left( s _ { \text { steel } } = 450 \mathrm { J } / \mathrm { kg } \mathrm { K } \right)$

physics temperature and heat applications of convection convection transfer of heat

  1. $31.2 ^ { \circ } C$

  2. $61.7 ^ { \circ } \mathrm { C }$

  3. $92.1 ^ { \circ } C$

  4. $42.1 ^ { \circ } C$

Show answer
Correct Option: B
Explanation:

$\large \begin{array}{l} According\, to\, question............. \ Here, \ \, \, \, \, \, m=1200kg,\, \, \, break\, drum\, (m)=10kg \ \, \, \, \, u=100km/h=27.77m/s \ \, \, \, \, { S _{ Steel } }=450J/KgK,\, \, \, \, \, V=0\, m/s \ so,\,  \ Energy\, released\, during\, breaking=\, \, change\, in\, kinetic\, energy \ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, =\frac { 1 }{ 2 } m{ v^{ 2 } }-\frac { 1 }{ 2 } m{ u^{ 2 } } \ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, =\frac { 1 }{ 2 } (1200)\, { (0)^{ 2 } }-\frac { 1 }{ 2 } (1200)\, { (27.77)^{ 2 } } \ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, =0-462937.0374\, J \ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, =462937.0374\, J \ Now, \ \, \, 60\quad perecent\quad of\, this\, energy\, appears=0.6\times 462937.0374\, J=277762.225 \ For\, change\, in\, temperature:\, \, \, \, ms\Delta \frac { 1 }{ 2 } t=277762.225 \ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \Rightarrow \Delta t=\dfrac { { 277762.225 } }{ { ms } } =\dfrac { { 277762.225 } }{ { 10\times 450 } }  \ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \therefore \, \, \, \, \Delta t\, ={ 61.7^{ 0 } }C \ so\, \, the\, correct\, option\, is\, B. \end{array}$

While measuring the thermal conductivity of liquids, the upper part is kept hot and lower one cool so that :

physics thermal energy transfers applications of convection convection transfer of heat

  1. convectional flow is stopped

  2. radiation is stopped

  3. conduction is easier

  4. it is easier to perform the experiment

Show answer
Correct Option: A
Explanation:

Heat flows from hotter part to colder part and the above arrangement is done to avoid convection currents.

Fireman crawl when entering a burning building because:

physics transfer of heat applications of convection convection thermal energy transfers

  1. It is easier to crawl

  2. Smoke rises high in the air

  3. It helps to move faster

  4. To resist more heat

Show answer
Correct Option: B
Explanation:

Smoke is lighter than air so it rises above the air, hence it is easier to breath crawling than while standing up.

Convection of heat takes place in:

physics thermal energy transfers applications of convection convection transfer of heat

  1. Metals only

  2. Liquids only

  3. Gases only

  4. Liquids and gases

Show answer
Correct Option: D
Explanation:

The molecules of liquids and gases are not rigidly bound to each other and can move freely. This makes the transfer of heat by convection possible.