Tag: refraction of light

Quizzes (6) Questions (50)

Questions Related to refraction of light

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 $i$. The reflected and refracted rays make an angle of $\pi/2$ with each other. If the angles of reflection and refraction are $r$ and $r'$, then the critical angle will be

  1. $\tan^{-1}(\sin i)$

  2. $\sin^{-1}(\sin r)$

  3. $\sin^{-1}(\tan i)$

  4. $\sin^{-1}(\tan r)$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
as the reflected and refracted rays are 90 then the angle of refraction is $90-i$

according to Snell's law
$sini\mu _{r}=sin(90-i)$

$\mu _{r}=coti$

critical angle is $sin^{-1}\dfrac{1}{\mu _{r}}=sin^{-1}\dfrac{1}{coti}=sin^{-1}tani$
option $C$ is correct 
Multiple choice physics refraction of light optical fibre the critical angle, total internal reflection and optical fibre total internal reflection

A fish looks upward at an unobstructed overcast sky. What total angle does the sky appear to subtend? (Take refractive index of water is $\sqrt 2)$

  1. $180^o$

  2. $90^o$

  3. $75^o$

  4. $60^o$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
as the refractive index is $\sqrt{2}$ the critical angle is $sin^{-1}\dfrac{1}{\mu _{c}}=sin^{-1}\dfrac{1}{\sqrt{2}}=45^{\circ}$

 total angle the sky appear to subtend is $2\times 45 =90^{\circ}$

option $B$ is correct 
Multiple choice physics refraction of light optical fibre the critical angle, total internal reflection and optical fibre total internal reflection

A ray of light traveling in a transparent medium falls on a surface separating the medium from air at an angle of incidence of $45^o$. The ray undergoes total internal reflection. If n is the refractive index of the medium with respect to air, select the possible value(s) of n from the following

  1. 1.3

  2. 1.4

  3. 1.5

  4. 1.6
Reveal answer Fill a bubble to check yourself
C,D Correct answer
Explanation

$\mu _{min}=\dfrac{1}{sin45}=\sqrt{2}=1.414$


possible values of $\mu$ are $1.5$ and $1.6$ 

option $C,D$ are correct 

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

The critical angle for glass-air is $45^o$ for the light of yellow colour. State whether it will be less than, equal to, or more than $45^o$ for  blue light?

  1. more than $45^o$

  2. less than $45^o$

  3. same as $45^o$

  4. cant say
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to Snell's Law: $\dfrac{sin i _c}{sin r}=\dfrac{n _2}{n _1}$ and for critical angle of incidence $r=90^o$ and $n _2=1$


Blue light has higher refractive index than yellow light hence it's critical angle will be lower than yellow light.

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

The critical angle for glass-air is $45^o$ for the light of yellow colour. State whether it will be less than , equal to, or more than $45^o$ for  red light?

  1. more than $45^o$

  2. less than $45^o$

  3. same as $45^o$

  4. can't say
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to Snell's Law: $\dfrac{sin i _c}{sin r}=\dfrac{n _2}{n _1}$ and for critical angle of incidence $r=90^o$ and $n _2=1$


Red light has lower refractive index than yellow light hence it's critical angle will be higher than yellow light.

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

State the approximate value of the critical angle for (a) glass-air surface, (b) water-air surface (Given $\mu _{glass} =1.5, \mu _{water}=1.33$)

  1. (a) $49^o$, (b)$49^o$

  2. (a) $42^o$, (b)$42^o$

  3. (a) $42^o$, (b)$49^o$

  4. (a) $49^o$, (b)$42^o$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Critical angle is the angle of incidence from denser to rarer medium for which the angle of refraction is $%%90^o$
These angles for glass-air interface is $42^o$ and water-air interface is $49^o$

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

The critical angle for light going from medium X into medium Y is $\theta$. The speed of light in medium X is v, then speed of light in medium Y is

  1. $v(1 - cos \theta)$

  2. $v/sin \theta$

  3. $v/ cos \theta$

  4. $v cos \theta$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
critical angle condition:

${ \mu  } _{ X }\sin { \theta  } ={ \mu  } _{ Y }$

Given, speed of light in medium X is v

To find: speed of light in medium Y

$\dfrac { { \mu  } _{ Y } }{ { \mu  } _{ X } } =\sin { \theta  }$

Also, speed of light in medium $Y$ is $=\dfrac{v}{\mu _{rel}}=v\dfrac { { \mu  } _{ X } }{ { \mu  } _{ Y } }$

$=\dfrac { v }{ \sin { \theta  }  }$
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' in vacuum and the same light takes $'t _2'$ sec to travel 10 cm in a medium. Critical angle for corresponding medium will be

  1. $\displaystyle sin^{-1} \left ( \frac{10 t _2}{t _1 x} \right )$

  2. $\displaystyle sin^{-1} \left ( \frac{t _2 x}{10 t _1 } \right )$

  3. $\displaystyle sin^{-1} \left ( \frac{10 t _1}{t _2 x } \right )$

  4. $\displaystyle sin^{-1} \left ( \frac{t _1 x}{10 t _2 } \right )$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\displaystyle c = \frac{x}{t _1} , v = \frac{10}{t _2}$

$\displaystyle sin  i _c = \frac{1}{\mu} = \frac{v}{c} = \frac{10}{t _2} \times \frac{t _1}{x}$

$\Rightarrow     i _c = sin^{-1} \left ( \dfrac{10  t _1}{t _2 x} \right )$

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

A ray of light is travelling from glass to air. (Refractive index of glass $=1.5$). The angle of incidence is $50^o$.The deviation of the ray is

  1. $0^o$

  2. 80$^o$

  3. $50^o - sin^{-1} \displaystyle \left [ \frac{sin 50^o}{1.5} \right ]$

  4. $sin^{-1} \displaystyle \left [ \frac{sin 50^o}{1.5} \right ] - 50^o$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$^a\mu _g = 1.5$


$\therefore 1.5 = cosec  C$ 

Or, $C = 42^0$. 

Critical angle for glass $= 42^0$. Hence a ray of light incident at $50^0$ in glass medium undergoes total internal reflection. $\delta$ denotes the deviation of the ray.

$\delta = 180^o - (50^o + 50^o) $ or $\delta = 80^o$.

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

A light ray is incident at an angle ${30}^{o}$ on a transparent surface separating two media. If the angle of refraction is ${60}^{o}$ then critical angle is

  1. $\sin ^{ -1 }{ \left( \cfrac { 1 }{ \sqrt { 3 } } \right) } $

  2. $\sin ^{ -1 }{ \left( \sqrt { 3 } \right) } $

  3. $\sin ^{ -1 }{ \left( \cfrac { 2 }{ 3 } \right) } $

  4. ${45}^{o}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Snell's law gives ${\mu} _{1} \sin {{30}^{o}}={\mu} _{2} \sin {{60}^{o}}$ but critical angle



${\theta} _{c}=\sin ^{ -1 }{ \left( \cfrac { { \mu  } _{ 2 } }{ { \mu  } _{ 1 } }  \right)  } =\sin ^{ -1 }{ \left( \cfrac { \sin { { 30 }^{ o } }  }{ \sin { { 60 }^{ o } }  }  \right)  } =\sin ^{ -1 }{ \left( \cfrac { 1 }{ \sqrt { 3 }  }  \right)  } $