The figure shows a ray of light falling normally on the face AB of an equilateral glass prism having a refractive index 3 / 2 , placed in water of refractive index 4 / 3 . Will this ray suffer total internal reflection on striking the face AC? Justify your answer.

It is given that the glass prism is equilateral. μ p = 3 / 2 μ w = 4 / 3 Thus, ∠ A = 60 ° . Let us draw a normal to the face AC. From the geometry, we can see, the angle of incidence on the face AC is 60 ° . Thus, i = 60 ° . Let this angle be the critical angle i.e. i = i c . Then the refractive index of the prism in the air, μ = 1 sin i c = 1 sin 60 ° μ = 2 3 = 1 . 54 Now if the prism is placed in water then the refractive index of a prism with water, μ A = μ p μ w = 3 2 4 3 = 9 8 = 1 . 125 The total internal reflection at face AC, is possible only when μ < μ A . But from the results obtained above, we can see that μ > μ A ∴ 1 . 54 > 1 . 125 No total internal reflection takes place and the light ray gets refracted from the prism placed in water. Thus, we can conclude that for total internal reflection, in this case, the Critical angle should be greater than 60 ° .

An object is placed in front of a concave mirror. It is observed that a virtual image is formed. Draw the ray diagram to show the image formation and hence derive the mirror equation 1 f = 1 u + 1 v .

Ray diagram to show the formation of a virtual image by concave mirror: Derivation of mirror equation using the above ray diagram: ∆ C A ' B ' and ∆ C A B are similar triangles. Hence, we can write: A ' B ' A B = C B ' C B = C P + P B ' C P - B P .......(i) D N is equal to A B and is a normal on the principal axis. ∆ F D N and ∆ F A ' B ' are similar triangles. The incident rays are considered to be paraxial rays hence, D and P are very close. We can write: A ' B ' A B = F B ' F D = F P + P B ' F D = F P + P B ' F P .....(ii) Using the above equations and substituting the values according to the sign convention we get: C P + P B ' C P - B P = F P + P B ' F P - 2 f + v - 2 f + u = - f + v - f ⇒ - 2 f 2 - f v = 2 f 2 - f u - 2 v f = u v ⇒ f u + f v = u v f On dividing both sides by u v f we get: 1 u + 1 v = 1 f The above equation is the required mirror equation.

Larger aperture of objective lens in an astronomical telescope _____

increases the resolving power of telescope.

decreases the brightness of the image.

increases the size of the image.

decreases the length of the telescope.

HARD

12th Meghalaya Board

IMPORTANT

Earn 100

What is chromatic aberration? What causes it?

Important Questions on Ray Optics and Optical Instruments

HARD

12th Meghalaya Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Ray Optics and Optical Instruments>Exercise>Q 63

Which type of telescopes can be made using a concave mirror, convex mirror, plane mirror and a lens? Draw diagrams of these telescopes.

HARD

12th Meghalaya Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Ray Optics and Optical Instruments>Exercise>Q 64

Explain the construction of Galileo’s telescope.

MEDIUM

12th Meghalaya Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Ray Optics and Optical Instruments>Exercise>Q 65

Draw a ray diagram for a monochromatic ray refracting from a glass prism. Write the expression for refractive index of glass in terms of prism angle and angle of minimum deviation.

MEDIUM

12th Meghalaya Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Ray Optics and Optical Instruments>Exercise>Q 66

The distance between two point sources of light is

24 cm

. Where should a convex lens of focal length

9 cm

be placed so that the images of both the sources are formed at the same point?

HARD

12th Meghalaya Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Ray Optics and Optical Instruments>Exercise>Q 67

Define Snell's Law. Using a neat labelled diagram derive an expression for the refractive index of the material of an equilateral prism.

HARD

12th Meghalaya Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Ray Optics and Optical Instruments>Exercise>Q 68

Show the nature of the

i - 𝛿

curve for a prism. Analyse the curve to show that for any particular value of

𝛿

, the difference between the fixed values of

i

and

e

decrease with the decrease of

𝛿

and becomes zero for

𝛿

minimum.

MEDIUM

12th Meghalaya Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Ray Optics and Optical Instruments>Exercise>Q 69

Give a short note on Cassegrain Telescope.

MEDIUM

12th Meghalaya Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Ray Optics and Optical Instruments>Exercise>Q 70

An infinitely long cylinder of radius $R$ is made of an unusual exotic material with refractive index –1 (Figure). The cylinder is placed between two planes whose normals are along the $y$ direction. The centre of the cylinder $O$ lies along the $y$ -axis. A narrow laser beam is directed along the $y$ direction from the lower plate. The laser source is at a horizontal distance $x$ from the diameter in the $y$ direction. Find the range of $x$ such that light emitted from the lower plane does not reach the upper plane.

Question Image

What is chromatic aberration? What causes it?

Important Questions on Ray Optics and Optical Instruments

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