i. Which of the following quantities is not changed during refraction of light?




... Answer is (c) its frequency
Frequency of light does not change on refraction. When a ray of light passes from one medium to another, its direction (or path) changes because of change in speed of light from one medium to another.


ii. A converging mirror with a radius of 20 cm creates a real image 30 cm from the mirror. What is the object distance?




... Answer is (c) -15 cm
According to the New Cartesian Sign Convention of Concave and Convex Lens, the distances measured in the direction opposite to the direction of incident light are taken as negative(-ve). Distances measured in the same direction as the incident light are taken as positive (+ve). Given: Radius of Curvature R= 20 cm so Focal Length f= - R / 2 = - 20 / 2 = -10 cm (-ve for real image) image distance q = -30 cm To Find: Object Distance p = ? Solution: So in this case i.e for a converging (concave) mirror, The image distance (q) and focal length (f) are negative for a real image. The and Object distance (p) will also be negative sign Mirror Formula 1/p+1/q=1/f ⇒ p = (f q) /(q - f) Putting values ⇒ p = (-10 x -30) /(-30 - (-10)) ⇒ p = 300 / -20 ⇒ p = -15 cm The negative sign indicates that the object is on the reflecting side as the mirror.


iii. An object is placed at the centre of curvature of a concave mirror. The image produced by the mirror is located:




... Answer is (b) at the centre of curvature
 When an object is placed at the centre of curvature, the real image is formed at the centre of curvature. The size of the image is the same as compared to that of the object.


iv. An object is 14 cm is in front of a convex mirror. The image is 5.8 cm behind the mirror. What is the focal length of the mirror?




... Answer is (c) -9.9cm
Given: p = object distance = + 14 cm (+ve sign is for the object is in front of the mirror) q = image distance = - 5.8 cm ( -ve sign is for image located behind the face of the mirror) To Find: f = focal length: ( -ve )? ( For a convex mirror the focal length 'f' is negative because it is located behind the face of the mirror. So, our answer will be with -ve sign) Solution: Using mirror formula, 1/f = 1/p + 1/q 1 /f = (q + p ) / pq f= pq / (q + p ) (putting values as given we get) f = -81.2 / 8.2 f = - 9.9 cm


v. The index of refraction depends on




... Answer is (b) the speed of light
Refractive index, also called index of refraction, describes how fast light travels through the material. It is defined as n = c/v. where c is the speed of light in vacuum and v is the phase velocity of light in the medium.


vi. Which type of image is formed by a concave lens on a screen?




... Answer is (d) upright and virtual
 A concave lens always produces virtual, erect and diminished images and the decrease in the size of the image depends on the position of the object.


vii. Which type of image is produced by the converging lens of human eye if it views a distant object? :




... Answer is (b) real, inverted, diminished
The eye lens, which is a double convex lens forms a real, inverted and highly diminished image of distant objects on the retina.


viii. Image formed on a camera is




... Answer is (a) real, inverted, and diminished
For photographic camera, the object is mostly beyond 2f (not at infinity). So the image thus produced lies in between f and 2f and will be real and inverted and diminished.


ix.. If a ray of light in glass is incident on an air surface at an angle greater than the critical angle, the ray will




... Answer is (b) reflect only
In Optics Critical angle is the greatest angle at which a ray of light totally reflected with the same medium when travelling from denser medium (Glass) and strike the rare medium (air).
 

x.. The critical angle for a beam of light passing from water into air is 48.8 degrees. This means that all light rays with an angle of incidence greater than this angle will be




... Answer is (b) totally reflected
In Optics Critical angle (48.8 degrees of water in this case) is the greatest angle at which a ray of light totally reflected with the same medium when travelling from denser medium (Water in this case) and strike the rare medium (air).
 

Note: If you are now confident to answer correctly for the above MCQs, than you can examine yourself by taking this Simple MCQS Quiz (Click here to play the Quiz)
 
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