Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

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

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

  1. increases with increase in resistance

  2. increases with increase in applied potential

  3. increases with decrease in resistance

  4. is constant
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Heat generated across the resistor is given by

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

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

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?

  1. $50.0J$

  2. $83.14J$

  3. $18J$

  4. $200J$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

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

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

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

James Prescott Joule performed experiments in the 1840s to demonstrate that heat is a form of energy. His work established the mechanical equivalent of heat, showing that a specific amount of mechanical work could produce a specific amount of heat.

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

Heat produced by the resistance R is:

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

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

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

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

From Joule's Law of heating-


Heat produced$=H=I^2Rt$

Now, $V=IR$

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

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

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

Multiple choice physics transfer of heat applications of convection convection thermal energy transfers

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

  1. sea and land breeze

  2. Boiling of water

  3. warming of glass of bulb due to filament

  4. heating air around a furnace
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
Multiple choice physics transfer of heat applications of convection convection thermal energy transfers

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 , $k _{glass}=0.8\,\,W\,\,m^{-1}K^{-1},K _{air}=0.08\,\,W\,\,m^{-1}K^{-1})$

  1. $41.5\,\,W$

  2. $31.5\,\,W$

  3. $21.5\,\,W$

  4. $11.5\,\,W$
Reveal answer Fill a bubble to check yourself
A Correct answer
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 $,H=\dfrac{\triangle T}{R}=\dfrac{27-0}{0.65}=41.5W$

Multiple choice physics temperature and heat applications of convection convection transfer of heat

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 $\left( s _ { \text { steel } } = 450 \mathrm { J } / \mathrm { kg } \mathrm { K } \right)$

  1. $31.2 ^ { \circ } C$

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

  3. $92.1 ^ { \circ } C$

  4. $42.1 ^ { \circ } C$
Reveal answer Fill a bubble to check yourself
B Correct answer
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}$

Multiple choice physics thermal energy transfers applications of convection convection transfer of heat

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

  1. convectional flow is stopped

  2. radiation is stopped

  3. conduction is easier

  4. it is easier to perform the experiment
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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