Tag: physics

Questions Related to physics

What is the angle of incidence if a ray of light is not deviated when it enters a block of glass?

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. $30^{\circ}$

  2. $60^{\circ}$

  3. $90^{\circ}$

  4. $0^{\circ}$

Show answer
Correct Option: D
Explanation:

The angle of incidence if a ray of light is not deviated when it enters a block of glass :

The angle of incidence is equal to angle of refraction only if the angle the  deviation is zero. This is practically impossible since, when light enters a medium from another medium it has to undergo refraction. So angle of minimum deviation is never zero but it can be a very small value. And angle of incidence is never equal to angle of refraction, if the light undergoes minimum deviation. But the angle of incidence is equal to the angle of emergence.

An under water swimmer looks upward at an unobstructed overcast sky. The vertex angle does the sky appear to subtend at the eye of swimmer is (critical angle for water air interface is  $C$).

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. $C$

  2. $C/2$

  3. $2 C$

  4. $3 C$

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Correct Option: C

A mark is made on the surface of a glass sphere of diameter 10 cm and refractive index 1.5 . it its viewed through the glass from a potion directly opposite . the distance of the image of the mark from the centre of the sphere will be 

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. 20 cm

  2. 17.5 cm

  3. 15 cm

  4. 22.5 cm

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Correct Option: A

When a ray of light strikes the glass slab at $90^{\circ}$, it is seen that it does not deviate from its path. In such a situation :

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. angle of incidence is zero

  2. angle of refraction is zero

  3. both(a) and (b)

  4. none of these

Show answer
Correct Option: C
Explanation:

 If the rays of light are incident upon the glass surface perpendicularly, or at 90 degree angle to the surface, the rays will pass through without changing direction. In this case, the angle of incidence and angle of refraction are always zero.
Hence, the option A and B are correct.

The velocity of light in air is $3\times 10^{10} cm/\sec$. If the refractive index of glass with respect to air is $1.5$, then velocity of light in glass is

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. $2\times 10^{10} cm/\sec$

  2. $4.5\times 10^{10} cm/\sec$

  3. $3\times 10^{10} cm/\sec$

  4. $1\times 10^{10} cm/\sec$

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Correct Option: A

A bird in air looks at a fish vertically elow it and inside water. X is the height of the bird above the surface of water and Y the depth of the fish below the surface of water if refractive index of water with respect to air is $ \mu $. The distance of the fish as observed by the bird is 

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. X + Y

  2. $ X + Y/ \mu $

  3. $ \mu X + Y $

  4. $ \mu X + \mu Y $

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Correct Option: C

A thin film of a liquid with refractive index $4/3$ produces interference pattern when light of wave length $450\ nm$ is incident normally. The minimum thickness of the film is approximately.

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. $1.68\times 10^{-7} m$

  2. $5.22\times 10^{-7} m$

  3. $4.5\times 10^{-7} m$

  4. $1.25\times 10^{-7} m$

Show answer
Correct Option: C

Point like object is observed using microscope angle subtended by objective with object is $20^{\circ}$. If oil of refractive index $1.4$ is kept between object and objective, numerical aperture will be ________.

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. $0.24$

  2. $0.48$

  3. $2.4$

  4. $4.8$

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Correct Option: C

A ray of light passes from a medium L to a medium K. No refraction of light occurs if the ray of light hits the boundary of these two media at the angle of incidence equal to ...............

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. $30^{\circ}$

  2. $90^{\circ}$

  3. $0^{\circ}$

  4. $120^{\circ}$

Show answer
Correct Option: B
Explanation:

If a light is an incident at an angle of $90^{o}$ it will go straight again making an angle of $90^{o}$ with the normal it doesn't depend on medium.
so the angle of incidence is $90^{o}$
A because if an angle of incidence is 90°, it means the light is propagating along the interface separating the two media. In this case, the light does not enter the second medium and so we can not talk about the angle of refraction. The angle of refraction can also be regarded as 90°.

The critical angle for refraction from medium -1 to air is ${ \theta  } _{ 1 }$ and that from medium -2 to air is ${ \theta  } _{ 2 }$. If medium -2 is denser then medium -1. Find the critical angle for refraction from medium -2 to medium. 

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. ${ sin }^{ -1 }(\frac { { sin\theta } _{ 2 } }{ { sin\theta } _{ 1 } } )$

  2. ${ sin }^{ -1 }(\frac { { sin\theta } _{ 1 } }{ { sin\theta } _{ 2 } } )$

  3. Both A and B

  4. None of these

Show answer
Correct Option: B
Explanation:

From medium 1 to air


$\eta _1sin\theta _1 = \eta _2sin\theta _2$

 here $\eta _2$ = 1 (air)

$\eta _1 = \frac{1}{sin\theta _1}$

Similarly for medium 2 to air

$\eta _2 = \frac{1}{sin\theta _2}$

Now from medium (2) to (1)

$\eta _2sin\theta _2 = \eta _1sin\theta _2$

$sin\theta _c = \frac{sin\theta _2}{sin\theta _1}$

$\theta _c = sin^{-1}(\frac{sin\theta _2}{sin\theta _1})$