Answer
Verified
89.7k+ views
Hint: If a ray of light goes from a denser medium to rarer medium. There is a particular angle beyond which the light rays will no longer refract but will be reflected totally. This phenomenon is called total internal reflection.
Formula Used:
The angle beyond which light rays reflect totally is called the critical angle. It is denoted as ${i_c}$.
The relation between critical angle and refractive index of the medium is given as
$\sin \,{i_c} = \dfrac{1}{n}$
Where $n$ is the refractive index.
From Snell’s law we know that refractive index is the ratio of sine of angle of incidence to the sine of angle of refraction.
Therefore,
$n = \dfrac{{\sin \,i}}{{\sin \,r}}$ (2)
Where, $i$ is the angle of incidence and $r$ is the angle of refraction
Complete step by step answer:
If a ray of light goes from a denser medium to rarer medium. There is a particular angle beyond which the light rays will no longer refract but will be reflected totally. This phenomenon is called total internal reflection. The angle beyond which light rays reflect totally is called the critical angle. It is denoted as ${i_c}$.
The relation between critical angle and refractive index of the medium is given as
$\sin \,{i_c} = \dfrac{1}{n}$ (1)
Where $n$ is the refractive index.
From Snell’s law we know that refractive index is the ratio of sine of angle of incidence to the sine of angle of refraction.
Therefore,
$n = \dfrac{{\sin \,i}}{{\sin \,r}}$ (2)
Where, $i$ is the angle of incidence and $r$ is the angle of refraction
Given the angle of incidence is ${45^ \circ }$and the refracted ray is deviated by ${15^ \circ }$.
Observe the figure above.
This means the angle of refraction can be calculated as,
$
r = {45^ \circ } - {15^ \circ } \\
= {30^ \circ } \\
$
Substituting the value of $i$ and $r$ in equation (2)
We get,
Refractive index as
$
n = \dfrac{{\sin \,{{45}^ \circ }}}{{\sin \,{{30}^ \circ }}} \\
= \dfrac{{\dfrac{1}{{\sqrt 2 }}}}{{\dfrac{1}{2}}} \\
= \sqrt 2 \\
$
Now using this value in equation 1 we get
$
\sin \,{i_c} = \dfrac{1}{n} \\
= \dfrac{1}{{\sqrt 2 }} \\
$
We need to find the angle ${i_c}$ therefore,
$
{i_c} = {\sin ^{ - 1}}\dfrac{1}{{\sqrt 2 }} \\
= {45^ \circ } \\
$
Critical Angle for glass air interface is ${45^ \circ }$.
Note: It is important to note that in this question angle of deviation is given instead of angle of refraction, we need to subtract the deviation from angle of incidence to find the angle of refraction and only then use it in Snell's Law.
Formula Used:
The angle beyond which light rays reflect totally is called the critical angle. It is denoted as ${i_c}$.
The relation between critical angle and refractive index of the medium is given as
$\sin \,{i_c} = \dfrac{1}{n}$
Where $n$ is the refractive index.
From Snell’s law we know that refractive index is the ratio of sine of angle of incidence to the sine of angle of refraction.
Therefore,
$n = \dfrac{{\sin \,i}}{{\sin \,r}}$ (2)
Where, $i$ is the angle of incidence and $r$ is the angle of refraction
Complete step by step answer:
If a ray of light goes from a denser medium to rarer medium. There is a particular angle beyond which the light rays will no longer refract but will be reflected totally. This phenomenon is called total internal reflection. The angle beyond which light rays reflect totally is called the critical angle. It is denoted as ${i_c}$.
The relation between critical angle and refractive index of the medium is given as
$\sin \,{i_c} = \dfrac{1}{n}$ (1)
Where $n$ is the refractive index.
From Snell’s law we know that refractive index is the ratio of sine of angle of incidence to the sine of angle of refraction.
Therefore,
$n = \dfrac{{\sin \,i}}{{\sin \,r}}$ (2)
Where, $i$ is the angle of incidence and $r$ is the angle of refraction
Given the angle of incidence is ${45^ \circ }$and the refracted ray is deviated by ${15^ \circ }$.
Observe the figure above.
This means the angle of refraction can be calculated as,
$
r = {45^ \circ } - {15^ \circ } \\
= {30^ \circ } \\
$
Substituting the value of $i$ and $r$ in equation (2)
We get,
Refractive index as
$
n = \dfrac{{\sin \,{{45}^ \circ }}}{{\sin \,{{30}^ \circ }}} \\
= \dfrac{{\dfrac{1}{{\sqrt 2 }}}}{{\dfrac{1}{2}}} \\
= \sqrt 2 \\
$
Now using this value in equation 1 we get
$
\sin \,{i_c} = \dfrac{1}{n} \\
= \dfrac{1}{{\sqrt 2 }} \\
$
We need to find the angle ${i_c}$ therefore,
$
{i_c} = {\sin ^{ - 1}}\dfrac{1}{{\sqrt 2 }} \\
= {45^ \circ } \\
$
Critical Angle for glass air interface is ${45^ \circ }$.
Note: It is important to note that in this question angle of deviation is given instead of angle of refraction, we need to subtract the deviation from angle of incidence to find the angle of refraction and only then use it in Snell's Law.
Recently Updated Pages
Name the scale on which the destructive energy of an class 11 physics JEE_Main
Write an article on the need and importance of sports class 10 english JEE_Main
Choose the exact meaning of the given idiomphrase The class 9 english JEE_Main
Choose the one which best expresses the meaning of class 9 english JEE_Main
What does a hydrometer consist of A A cylindrical stem class 9 physics JEE_Main
A motorcyclist of mass m is to negotiate a curve of class 9 physics JEE_Main
Other Pages
A block of mass 5 kg is on a rough horizontal surface class 11 physics JEE_Main
A pendulum clock keeps the correct time at 20 degrees class 11 physics JEE_Main
If a wire of resistance R is stretched to double of class 12 physics JEE_Main
Derive an expression for maximum speed of a car on class 11 physics JEE_Main
The diagram given shows how the net interaction force class 11 physics JEE_Main
Which of the following meet the requirements of Huckel class 11 chemistry JEE_Main