Tag: physics

Questions Related to physics

Which of the following conclusion can be drawn from the result $\oint \bar{B}\cdot d\bar{A}=0$

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. Magnetic field is zero everywhere

  2. Magnetic monopole cannot exist

  3. Magnetic lines of force do not intersect each other

  4. A current produces magnetic field

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Correct Option: B
Explanation:

Flux of certain closed surface is zero and so it tells that net magnetic charge is equal to zero. This is possible when there are two equal and opposite poles.

Which of the following effects could not be explained by Maxwell's electromagnetic wave theory?

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. Photoelectric effect

  2. Compton effect

  3. Raman effect

  4. All of these

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Correct Option: D
Explanation:

  1. Photoelectric effect was discovered by heinrich Rudoy Hertz.
  2. Compton effect was discovered by Aethur Holl Compton.
  3. Raman effect was discovered by Sir Chandrasekhar Venbata Ram. 
      So, none of these effect was discovered by Maxwell.

A parallel plate capacitor having plate area A and plate separation $d$ is connected to a battery of emf $\varepsilon$ and internal resistance $R$ at $t=0$. Consider a plane surface of area $\dfrac{A}{2}$, parallel to the plates and situated symmetrically between them. Find the displacement current through this surface as a function of time?

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. $\dfrac {-\varepsilon}{2R} \ \ \ e^{\dfrac{-td}{\varepsilon AR}}$

  2. $\dfrac {2\varepsilon}{R} \ \ \ e^{\dfrac{-td}{\varepsilon AR}}$

  3. $\dfrac {5\varepsilon}{2R} \ \ \ e^{\dfrac{-td}{4 \varepsilon AR}}$

  4. $\dfrac {\varepsilon}{2R} \ \ \ e^{\dfrac{-td}{4\pi \varepsilon AR}}$

Show answer
Correct Option: A

According to Maxwell's hypothesis, changing of electric filed give rise to

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. magnetic field

  2. pressure gradient

  3. charge

  4. voltage

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Correct Option: A
Explanation:

According to Maxwell's hypothesis, changing of electric field gives rise to Magnetic field.

We know that $F=qE,$, where $F$ is force and $E$ is electric field.
We can relate magnetic field and force by $F=qvB$, where $v$ is velocity and $B$ is the magnetic field.
Therefore we can obtain magnetic field by changing electric field.
Therefore option $A$ is correct.

Unpolarized light falls first on polarizer $\left( P \right) $ and then on analyzer $\left( A \right) $. If the intensity of the transmitted light from the analyser is $\dfrac { 1 }{ 8 }$th of the incident unpolarized light. What will be the angle between optic axes of $P$ and $A$?

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. ${ 45 }^{ o }$

  2. ${ 30 }^{ o }$

  3. Zero

  4. ${ 60 }^{ o }$

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Correct Option: D
Explanation:

Given,
$I=\dfrac { { I } _{ 0 } }{ 2 } $              ....(i)
${ I }^{ ' }=I\cos ^{ 2 }{ \theta  } $                 $\left( \because { I }^{ ' }=\dfrac { { I } _{ 0 } }{ 8 }  \right) $
$\therefore \dfrac { { I } _{ 0 } }{ 8 } =\dfrac { { I } _{ 0 } }{ 2 } \cos ^{ 2 }{ \theta  } $
From the equation (i), we have
$\dfrac { 1 }{ 4 } =\cos ^{ 2 }{ \theta  } \Rightarrow \cos { \theta  } ={ 1 }/{ 2 }$
$\Rightarrow \cos { \theta  } =\cos { { 60 }^{ o } } $
$\Rightarrow \theta ={ 60 }^{ o }$

A plane electromagnetic wave with an intensity of $200 W/m^2$ is incident normal to a flat plate of radius 30 cm. If the plate absorbs $60%$ and reflect $40%$ of the incident radiation, what is the momentum transferred to it in 5 min?

physics option a: relativity maxwell's equations the nature of light introduction to electromagnetic waves

  1. $1.7 \times 10^{-3} kg ms^{-1}$

  2. $2.7 \times 10^{-4} kg ms^{-1}$

  3. $3.7 \times 10^{-4} kg ms^{-1}$

  4. $3.7 \times 10^{-3} kg ms^{-1}$

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Correct Option: A

If refraction index of glass with respect to air is $ _{a}{u} _{g} = \dfrac{3}{2}$, the refraction index of air with respect to glass will be $ _{g}{u} _{a} =$

physics light : reflection and refraction from plane surface principle of reversibility of path of light image formation by plane mirror refractive index

  1. ${3}/{2}$

  2. ${2}/{3}$

  3. ${1}/{3}$

  4. ${1}/{2}$

Show answer
Correct Option: B
Explanation:
refractive index of glass w.r.t air =${ _{ a }{ \mu  } _{ g }= }\dfrac { 3 }{ 2 } $
then,
refractive index of air w.r.t glass  =$ _{ g }{ \mu  } _{ a }=\dfrac { 1 }{ _{ a }{ \mu  } _{ g } } $

$ _{ g }{ \mu  } _{ a }=\dfrac { 1 }{ _{ a }{ \mu  } _{ g } } =\dfrac { 2 }{ 3 } $
Option B is correct.

The refractive index of water with respect to air is $ _{a}{u} _{w}$ and of glass with respect to air is $ _{a}{u} _{g}$. Express the refractive index of glass with respect to water

physics light : reflection and refraction from plane surface principle of reversibility of path of light image formation by plane mirror refractive index

  1. $\dfrac{ _{a}{u} _{g}}{ _{a}{u} _{w}}$

  2. $\dfrac{ _{g}{u} _{a}}{ _{a}{u} _{w}}$

  3. $\dfrac{ _{a}{u} _{w}}{ _{a}{u} _{g}}$

  4. $\dfrac{ _{a}{u} _{a}}{ _{g}{u} _{g}}$

Show answer
Correct Option: A
Explanation:

Refractive index of water w.r.t air
$ _{a}\mu _{w}=\dfrac{\mu _{w}}{\mu _{a}}$
Refractive index of glass w.r.t air
$ _{a}\mu _{g}=\dfrac{\mu _{g}}{\mu _{a}}$
Hence refractive index of glass w.r.t water
$ _{w}\mu _{g}=\dfrac{\mu _{g}}{\mu _{w}}   =\dfrac{ _{a}\mu _{g}}{ _{a}\mu _{w}}$

At ray of light is incident in medium 1 at an angle of $37^{o}$ and gets refracted in medium 2 at an angle of $53^{o}$. What will be angle of refraction if light is incident in medium 2 at an angle of $53^{o}$.

physics light : reflection and refraction from plane surface principle of reversibility of path of light image formation by plane mirror refractive index

  1. $37^{o}$

  2. $53^{o}$

  3. $36^{o}$

  4. $45^{o}$

Show answer
Correct Option: A
Explanation:

Principle of reversibility states that when final path of a ray of light after any number of reflections and refractions is reversed, the ray retraces its entire path or in simple words, light follows exactly the same path if its path of travel is reversed.

Thus angle of refraction of light in medium $1$ will be $37^o$.

A real object is at a distance of 1 m from its virtial image formed by a diverging lens . Determine the focal length of the lens if magnification is  02.6 :- 

physics light : reflection and refraction from plane surface principle of reversibility of path of light image formation by plane mirror refractive index

  1. -3.25m

  2. -205m

  3. -3.75 m

  4. 1.25 m

Show answer
Correct Option: B