Define focal length of a concave mirror. Prove that the radius of curvature of a concave mirror is double its focal length.

The focal length of a concave mirror is the distance between the Pole and the principal focus. Consider the following figure of a concave mirror. Let C be the centre of curvature of the mirror. Consider a ray parallel to the principal axis striking the mirror at M . Then CM will be perpendicular to the mirror at M . Let θ be the angle of incidence, and MD be the perpendicular from M on the principal axis. Then, ∠ M C P = θ Also, ∠ M F P = 2 θ Now, tan θ = MD CD and tan 2 θ = MD FD For small θ which is true for paraxial rays, tan θ = θ and tan 2 θ = 2 θ Therefore, MD FD = 2 MD CD ⇒ FD = DC 2 Now, for small θ , the point D is very close to the point P . Therefore, FD = f and CD = R That means, f = R 2

A small angled prism of 4 ° deviates a ray through 2 . 48 ° . Find the refractive Index of the prism.

It is given that the prism under consideration is a thin prism. Also, The angle of prism, A = 4 ° Angle of deviation, δ = 2 . 48 ° Let n be the refractive index of the prism. We know that for a thin prism, δ = A n - 1 ⇒ n = δ A + 1 ⇒ n = 1 . 62

A concave mirror produces an image of a long vertical pin, placed 40 cm from the mirror, at the position of the object. Find the focal length of the mirror (in cm ).

When an object is placed at the centre of curvature of a concave mirror, a real, inverted image of the same size as the object will form at the centre of curvature itself. This is illustrated in the figure. It is given in the question that image is formed at the same position as the object. This implies that the object is placed at the centre of curvature. That means, radius of curvature, R = - 40 cm Therefore, focal length, f = - 40 2 ⇒ f = - 20 cm

E M B I B E

Intermediate Second Year Physics>Chapter 2 - Ray Optics and Optical Instruments>MODEL QUESTIONS (IPE PATTERN)>Q 3

EASY

12th Andhra Pradesh Board

IMPORTANT

Earn 100

A mobile phone lies along the principal axis of a concave mirror longitudinally. Explain why the magnification is not uniform.

Important Questions on Ray Optics and Optical Instruments

MEDIUM

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 2 - Ray Optics and Optical Instruments>MODEL QUESTIONS (IPE PATTERN)>Q 4

Explain the Cartesian sign convention for mirrors.

HARD

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 2 - Ray Optics and Optical Instruments>MODEL QUESTIONS (IPE PATTERN)>Q 5

Define critical angle. Explain total internal reflection using a neat diagram.

EASY

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 2 - Ray Optics and Optical Instruments>MODEL QUESTIONS (IPE PATTERN)>Q 6

Explain the formation of a mirage.

HARD

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 2 - Ray Optics and Optical Instruments>MODEL QUESTIONS (IPE PATTERN)>Q 7

Explain the formation of rainbow.

HARD

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 2 - Ray Optics and Optical Instruments>MODEL QUESTIONS (IPE PATTERN)>Q 9

With a neat labelled diagram explain the formation of image in a simple microscope.

HARD

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 2 - Ray Optics and Optical Instruments>MODEL QUESTIONS (IPE PATTERN)>Q 10

What is the position of the object for a simple microscope? What is the maximum magnification of a simple microscope for a realistic focal length?

HARD

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 2 - Ray Optics and Optical Instruments>MODEL QUESTIONS (IPE PATTERN)>Q 1

What is the cartesian sign convention? Applying this convention and using a neat diagram, derive an expression for finding the image distance using the mirror equation.

MEDIUM

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 2 - Ray Optics and Optical Instruments>MODEL QUESTIONS (IPE PATTERN)>Q 1

An object of $5 cm$ height is placed at a distance of $15 cm$ from a concave mirror of radius of curvature $20 cm$ . Find the size of the image.