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Questions Related to physics

Multiple choice physics refraction of light optical fibre the critical angle, total internal reflection and optical fibre total internal reflection

A ray of light travelling in a transparent medium falls on a surface separating the medium from air at an angle of incidence 45$^{\circ}$. The ray undergoes total internal reflection. The possible value of refractive index of the medium with respect to air is

  1. 1.245

  2. 1.324

  3. 1.414

  4. 1.524
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\mu _{medium} \times \sin 45^{\circ} =\mu _{air}$


$\dfrac{\mu _{medium}}{\mu _{air}}=\dfrac{1}{\sin 45^{\circ}}
=\sqrt{2}
=1.414$

Multiple choice physics refraction of light optical fibre the critical angle, total internal reflection and optical fibre total internal reflection

The critical angle of a medium B with respect another medium A is 45$^{\circ}$ and the critical angle of a medium C with respect the medium B is 30$^{\circ}$. The critical angle of medium C with respect to A is :

  1. Less than 30$^{\circ}$
  2. Greater than 30$^{\circ}$
  3. 30$^{\circ}$

  4. Cannot be determined
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$ \mu _{B} sin 45^{\circ}=\mu _{A} $


$ \mu _{C} sin 30^{\circ}=\mu _{B} $

$ \mu _{C} sin 30 sin 45=\mu _{A} $

$ \mu _{C} \dfrac{1}{2\sqrt{2}}=\mu{A} $

$ \therefore critical \ angle = sin ^{-1} \left ( \dfrac{1}{2\sqrt{2}} \right )<30^{\circ} $

Multiple choice physics refraction of light optical fibre the critical angle, total internal reflection and optical fibre total internal reflection

 Light takes t$ _{1}$ sec to travel a distance x cm in vacuum and takes t$ _{2}$ sec to travel 10x cm in a medium.  The critical angle corresponding to the media is :                         

  1. $sin^{-1}(10t _{1}/t _{2}$)
  2. $sin^{-1}(t _{2}/10$)
  3. $sin^{-1}(1/t _{1}$)
  4. $sin^{-1}(t _{1}/10t _{2}$)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\vartheta _{vaccum}=\dfrac{d _{vaccum}}{t _{vaccum}}=\dfrac{\chi }{t _{1}}$


$v _{med}=\dfrac{10\chi }{t _{2}}$

$\mu=\dfrac{\chi \times t _{2}}{t _{1}\times 10\chi }=\dfrac{t _{2}}{10t _{1}}$


$\theta _{cric}=sin^{-1}\left ( \dfrac{1}{\mu} \right )=sin^{-1}\left ( \dfrac{10t _{1} }{t _{2}}\right )$

Multiple choice physics refraction of light optical fibre the critical angle, total internal reflection and optical fibre total internal reflection

If the critical angle of the medium is 30$^{\circ}$, the velocity of light in that medium is :
(velocity of light in air  $3 \times 10^8 $ m/s)

  1. 6 x 10$^{8}$m/ s
  2. 3 x 10$^{8}$m /s
  3. 1.5 x 10$^{8}$m/ s
  4. 1 x 10$^{8}$m/s
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

As, $\theta _{cric}=sin^{-1}\left ( \dfrac{1}{\mu} \right )$


$ sin \theta _{cric}=\dfrac{1}{\mu} $

$ \mu= \dfrac{1}{sin 30}=2 $

Also as $ \mu= \dfrac{c}{v _m}=\dfrac{3\times 10^{8}}{v _m } $

$ v _m = 1.5 \times 10^{8} m/s. $

Multiple choice physics refraction of light optical fibre the critical angle, total internal reflection and optical fibre total internal reflection

A ray of light from a denser medium strikes a rarer medium at an angle of incidence $i$. If the reflected and refracted rays are mutually perpendicular to each other then the critical angle is :

  1. sin$^{-1}$ (tan i)
  2. cos$^{-1}$ (tan i)
  3. cot $^{-1}$ (tan i)
  4. cosec$^{-1}$ (tan i)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$i+r=90$  where i is the angle of incidence, r is the angle of refraction


$r=90-i$

From Snell's Law, $\mu \times sin i= 1 \times sin r$

$\mu \times sin i = sin \left ( 90-i \right )$

$\mu = cot\ i$

$\theta _{cric} =sin^{-1} \left ( \dfrac{1}{\mu} \right )=sin^{-1}\left ( tan\ i \right )$

Multiple choice physics refraction of light optical fibre the critical angle, total internal reflection and optical fibre total internal reflection

The critical angle for a medium with respect to air $45^0$. The refractive index of that medium with respect to air is:

  1. $\dfrac {\sqrt 3}{2}$
  2. $\dfrac {2}{\sqrt 3}$
  3. $\sqrt 2$
  4. $\dfrac {1}{\sqrt 2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$C=45^0$


$^{med}\mu _a=\dfrac {1}{sin C}=\dfrac {1}{sin 45^0}$

$=\dfrac {1}{(1\sqrt 2)}=\sqrt 2$

Multiple choice physics refraction of light optical fibre the critical angle, total internal reflection and optical fibre total internal reflection

A ray of light travelling in water is incident on its surface open to air. The angle of incidence is $\theta$, which is less than the critical angle. Then there will be?

  1. Only a reflected ray and no refracted ray

  2. Only a refracted ray and no reflected ray
  3. A reflected ray & a refracted ray and the $\angle$ between them would be less than $180^o-20^0$
  4. A reflected ray & a refracted ray and the $\angle$ between them would be greater than $180^o-2\theta$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

There will be a reflected ray and a refracted ray.since incident angle is less than critical angle, angle between two resultant rays would be between $180^{\circ} - 20^{\circ}$.hence option c

Multiple choice physics refraction of light optical fibre the critical angle, total internal reflection and optical fibre total internal reflection

A point source S is placed at the bottom of a transparent block of height 10 mm and refractive index 2.72. It is immersed in a lower refractive index liquid as shown in the figure. It is found that the light emerging from the block to the liquid forms a circular brightspot of diameter 11.54 mm on the top of the block. The refractive index of the liquid is

  1. 1.21

  2. 1.30

  3. 1.36

  4. 1.42
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

We have, 
$ Sin  C = [ 1 + \dfrac {\mu+b}{\mu _l}] = [\dfrac {\mu _1}{2.72}]$


$\implies [ \dfrac {r}{\sqrt {r^2 + h^2}}] = \dfrac {\mu _1}{2.72}$

$\implies \mu _1 = (\dfrac {2.72}{2}) = 1.36$

Multiple choice physics refraction of light optical fibre the critical angle, total internal reflection and optical fibre total internal reflection

A ray of light travelling in a transparent medium falls on a surface separating the medium from air at an angle of incidence $45^{\mathrm{o}}$ and undergoes total internal reflection. lf $\mu$ is the refractive index of medium the possible values of $\mu$ are

  1. $\mu =1.3$
  2. $\mu =1.4$
  3. $\mu =1.5$
  4. $\mu =1.6$
Reveal answer Fill a bubble to check yourself
C,D Correct answer
Explanation

Since, the ray undergoes total internal reflection, 
$ \mu > \dfrac{1}{sin c} $


Now,$ i = 45$

Thus, $sin \  c < sin  \ i $

Thus, $ \mu > \dfrac{1}{sin i} $

OR, $ \mu > \sqrt{2} $

Multiple choice physics heat and temperature thermal expansion in liquids anomalous expansion of water thermal expansion in solids, liquids and gases

Assertion(A): Real expansion of liquid does not depend up on material of container.

Reason (R): Liquids have no definite shape. They acquire the mouth of the containers in which they are taken.

  1. Both A and R are true and R is the correct explanation of A

  2. Both A & R are true but R is not the correct explanation of A.

  3. A is true but R is false

  4. A is false but R istrue
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Real expansion would not be affected by the size and shape of container. Because of liquid has no any definate shape.
Both assertion and reason are true and reason is correct explanation.