Ray Optics and Optical Instruments

Ray Optics and Optical Instruments

Easy Questions
Moderate Questions
Difficult Questions

Optics

Ray Optics and Optical Instruments
Wave Optics
  1. A person is six feet tall. How tall must a vertical mirror be if he is able to see his entire length? ​








  1. View Hint View Answer Discuss in Forum

    To see his full image in a plane mirror a person requires a mirror of at least half of his height.

    Correct Option: A

    To see his full image in a plane mirror a person requires a mirror of at least half of his height.

  1. A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is :​​​








  1. View Hint View Answer Discuss in Forum


    The focal length of the mirror

    -
    1
    		 =
    1
    		 +
    1
    fvu

    For A end of the rod the image distance ​When u1 = – 20 cm
    ⇒ -
    1
    		 =
    1
    		 -
    1
    10v120

    1
    		 =
    -1
    		 +
    1
    		 =
    -2 + 1
    v1102020

    v1 = – 20 cm ​
    For when u2 = – 30 cm
    1
    		 =
    1
    		 -
    1
    fv230

    1
    		 =
    -1
    		 -
    1
    		 =
    -30 + 10
    		 =
    -20
    v21030300300

    v2 = – 15 cm
    L = v2 – v1 = – 15 – (– 20) ​
    L = 5 cm

    Correct Option: D


    The focal length of the mirror

    -
    1
    		 =
    1
    		 +
    1
    fvu

    For A end of the rod the image distance ​When u1 = – 20 cm
    ⇒ -
    1
    		 =
    1
    		 -
    1
    10v120

    1
    		 =
    -1
    		 +
    1
    		 =
    -2 + 1
    v1102020

    v1 = – 20 cm ​
    For when u2 = – 30 cm
    1
    		 =
    1
    		 -
    1
    fv230

    1
    		 =
    -1
    		 -
    1
    		 =
    -30 + 10
    		 =
    -20
    v21030300300

    v2 = – 15 cm
    L = v2 – v1 = – 15 – (– 20) ​
    L = 5 cm

  1. Two plane mirrors are inclined at 70°. A ray incident on one mirror at angle θ after reflection falls on second mirror and is reflected from there parallel to first mirror. The value of θ is








  1. View Hint View Answer Discuss in Forum


    From fig. 40° + θ = 90°
    ∴ θ = 90° – 40° = 50°

    Correct Option: A


    From fig. 40° + θ = 90°
    ∴ θ = 90° – 40° = 50°

  1. Match the corresponding entries of column-1 with column-2 (Where m is the magnification produced by the mirror) : ​​
    Column-1 Column-2
    (P) m = – 2(A) Convex mirror
    (Q) m = - 1 / 2 (B) Concave mirror
    (R) m = + 2 (C) Real image
    (S) m = + 1 / 2 (D) Virtual image








  1. View Hint View Answer Discuss in Forum

    Magnitude m = +ve ⇒ virtual image ​m = –ve ⇒ real image ​
    magnitude of magnification, ​
    | m | > 1 ⇒ magnified image ​
    | m | < 1 ⇒ diminished image

    Correct Option: A

    Magnitude m = +ve ⇒ virtual image ​m = –ve ⇒ real image ​
    magnitude of magnification, ​
    | m | > 1 ⇒ magnified image ​
    | m | < 1 ⇒ diminished image

  1. A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source I. When the mirror is rotated through a small angle θ, the spot of the light is found to move through a distance y on the scale. The angle θ is given by








  1. View Hint View Answer Discuss in Forum

    When mirror is rotated by  angle θ reflected ray will be rotated by 2θ.

    y
    		 = 2θ ⇒ θ =
    y
    x2x

    Correct Option: D

    When mirror is rotated by  angle θ reflected ray will be rotated by 2θ.

    y
    		 = 2θ ⇒ θ =
    y
    x2x