Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

Multiple choice physics electric charges and fields potential energy of a dipole in external field potential due to electric dipole electric dipole

An electric dipole has the magnitude of its charge as q and its dipole moment is p. It is placed in a uniform electric field E. If its dipole moment is along the direction of the field, the force on it and its potential energy are respectively:

  1. q. E and p. E

  2. zero and minimum

  3. q. E and maximum

  4. 2q. E and minimum
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$F = p\dfrac{dE} {dr} = 0 \left ( \because E = constant \right )$
$u = -\overrightarrow{p} \overrightarrow{E} = -PE \left ( minimum \right )$

Multiple choice physics electric charges and fields potential energy of a dipole in external field potential due to electric dipole electric dipole

Intensity of an electric field (E) depends on distance $r$. In case of dipole, it is related as :

  1. $ E \propto \cfrac{1}{r}$

  2. $ E \propto \cfrac{1}{r^{2}}$

  3. $ E \propto \cfrac{1}{r^{3}}$

  4. $ E \propto \cfrac{1}{r^{4}}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Intensity of electric field due to a Dipole
$ E = \cfrac{p}{4\pi \varepsilon _{0}r^{3}} \sqrt{3cos^{2 }\theta+1}\Rightarrow E \propto \cfrac{1}{r^{3}}$

So, we can just dimensionally tell that Electric field will be inversely proportional to third power of $r$.

Multiple choice physics electric charges and fields potential energy of a dipole in external field potential due to electric dipole electric dipole

A point charge $Q$ lies on the perpendicular bisector of an electric dipole of dipole $p$. If the distance of $Q$ from the dipole is $r$ (much larger than the size of the dipole).then the electric field at $\theta$ is proportional to :

  1. $P^{2}$ and $r^{-3}$

  2. $P$ and $r^{-2}$

  3. $P^{-1}$ and $r^{-2}$

  4. $P$ and $r^{-3}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$\begin{array}{l} As\, \, we\, \, have, \ if\, \, r>1 \ { P _{ axi } }=\frac { 1 }{ { 4\pi { E _{ 0 } } } } \frac { { 2P } }{ { { r^{ 3 } } } }  \ { V _{ axi } }=\frac { 1 }{ { 4\pi { E _{ 0 } } } } \frac { P }{ { { r^{ 2 } } } }  \ Where\, \, in, \ Angle\, \, between\, \, { P _{ axi } }\, \, and\, \, P\, \, is\, 0. \ { E _{ equatorial } }=\frac { { kp } }{ { { r^{ 3 } } } }  \ i.e\, \, \, E\propto p \ and\, \, P\propto { r^{ -3 } } \end{array}$

Hence, Option $D$ is correct answer.

Multiple choice physics measurement and effects of heat thermal expansion in gases thermal expansion of fluids volume elasticity constant of gases

At constant pressure how much fraction of heat supplied to gas is converted into mechanical work ?  

  1. $\dfrac { \gamma -1 }{ \gamma } $

  2. $\dfrac { \gamma }{ \gamma -1 } $

  3. $\gamma -1$

  4. $\dfrac { \gamma }{ \gamma +1 } $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

At constant pressure, dQ = nCp dT and dW = P dV = nR dT. The fraction of heat converted to work is dW/dQ = (nR dT) / (nCp dT) = R/Cp. Since Cp = gamma*R / (gamma-1), the fraction is R / (gamma*R / (gamma-1)) = (gamma-1)/gamma.

Multiple choice physics measurement and effects of heat thermal expansion in gases thermal expansion of fluids volume elasticity constant of gases

A gas compressed to half of its volume at ${30}^{o}C$. Upto what temperature should it be heated, so that its volume increase to double of its original volume?

  1. ${60}^{o}C$

  2. $303K$

  3. $606K$

  4. $1212K$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using P1V1/T1 = P2V2/T2. Since pressure is constant, V1/T1 = V2/T2. V1 = V, V2 = 2V. T1 = 30 + 273 = 303K. V/303 = 2V/T2. T2 = 606K.

Multiple choice physics measurement and effects of heat thermal expansion in gases thermal expansion of fluids volume elasticity constant of gases

A gas follows $VT^2 =$ const. Its volume expansion coefficient will be :-

  1. $\dfrac{2}{T}$

  2. $-\dfrac{2}{T}$

  3. $\dfrac{3}{T}$

  4. $-\dfrac{3}{T}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\begin{array}{l} \gamma =\dfrac { 1 }{ V } \left( { \dfrac { { dV } }{ { dT } }  } \right)  \ P{ T^{ 2 } }=cons\tan  t \ \dfrac { { nRT } }{ V } { T^{ 2 } }=cons\tan  t \ \therefore \gamma =\dfrac { 3 }{ T }  \ Hence,\, C\, the\, \, correct\, option\, .\,  \end{array}$

Multiple choice physics measurement and effects of heat thermal expansion in gases thermal expansion of fluids volume elasticity constant of gases

A one litre flask contain some mercury. It is found that at different temperatures the volume of air inside the flask remain same. the volume of mercury taken in the flask is (coefficient of linear expansion of volume expansion of $Hg$ is $1.8\times { 10 }^{ -4 }/ _{  }^{ o }{ C }$ 

  1. $150ml$

  2. $750ml$

  3. $1000ml$

  4. $700ml$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For the volume of air to remain constant, the expansion of the mercury must equal the expansion of the flask. V_Hg * gamma_Hg * dT = V_flask * gamma_flask * dT. Assuming gamma_flask is negligible or given, we solve for V_Hg. If gamma_flask is 0, V_Hg = V_flask * (gamma_flask/gamma_Hg). The question implies a specific balance.

Multiple choice physics measurement and effects of heat thermal expansion in gases thermal expansion of fluids volume elasticity constant of gases

A uniform steel rod has length $\ell$ at $0^oC$. Now one of its end is kept in ice $(0^oC)$ and the other end is kept in steam $(100^oC)$. If the coefficient of thermal expansion of the rod is $\alpha,$how much is the thermal expansion of the rod at steady state? 

  1. $50\ \alpha\ell$

  2. $100\ \alpha\ell$

  3. $200\ \alpha\ell$

  4. $150\ \alpha\ell$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Thermal expansion is defined as the change in length due to a change in temperature. Since the rod is at steady state with one end at 0C and the other at 100C, the temperature varies linearly along the rod, resulting in an average temperature of 50C. The expansion is given by delta L = L * alpha * delta T, where delta T is the difference between the average temperature and the initial temperature (50 - 0 = 50).

Multiple choice physics measurement and effects of heat thermal expansion in gases thermal expansion of fluids volume elasticity constant of gases

An inflated rubber balloon contains one mole of an ideal gas. Has a pressure p, volume V and temperature T. if the temperature rises to 1.1 T, and the volume is increase to 1.05 V, the final pressure will be:

  1. 1.04p

  2. 1.2 p

  3. less than p

  4. between p and 1.1.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$PV=nRT\rightarrow (1)\ P _1(1.05V)=nR(1.1T)\rightarrow (2)\ \Rightarrow (1)\div(2)\ \Rightarrow \cfrac{P}{1.05P _1}=\cfrac{1}{1.1}\ \Rightarrow P _1=\cfrac{1.1P}{1.05}=1.047P$