1. Dispersive power of the material of the prism is 0.0221. If the deviation produced by it for yellow color is 38°, then the angular dispersion between red and violet color is?
a) 0.84°
b) 0.65°
c) 0.48°
d) 1.26°
Explanation: Angular dispersion = deviation produced * dispersive power
angular dispersion = (38°) * (0.0221)
therefore, angular dispersion = 0.8398° Ξ 0.84°.
2. What is the lens?
a) An image – forming device
b) An image – producing device
c) An image – reflecting device
d) An object – reflecting device
Explanation: A lens is an image- forming device. They form an image by refraction of light at its two bounding surfaces
3. The spherical surface of lens results in ________
a) having a wide range of focal length
b) having a narrow range of focal length
c) having a wide range of curvature
d) having a narrow range of curvature
Explanation: Most lenses are made of spherical surfaces because spherical surfaces are easy to make and have wide range of curvature. Hence, the spherical surface of lens only results in having a wide range of curvature, not wide range of focal length.
4. What are Concave lenses?
a) Thicker from the centre than at the edge
b) Thinner from the centre than at the edge
c) Thicker from both the positions
d) Thinner from both the positions
Explanation: Concave lenses are thinner from the centre than at the edge. However, convex lenses are thicker from the centre than at the edge.
5. Out of the following which one is diverging or negative lens?
a) Biconvex
b) Plano-convex
c) Biconcave
d) Positive meniscus
Explanation: Biconcave is the diverging or negative lens. Whereas biconvex, plano-convex and positive meniscus are converging or positive lenses
6. What is the reciprocal, of the length of radius of curvature?
a) Focal length
b) Curvature
c) Optical centre
d) Power
Explanation: The reciprocal of length of radius of curvature is called curvature.
i.e., C=1/R
while, the reciprocal of focal length is power.
i.e., P=1/f
A lens has two centres of curvature, also it has two radii of curvature, one for each of the refracting surface.
7. Where does the principal axis intersect the two refracting surfaces?
a) Front vertex and back vertex
b) Focal length
c) Radius of curvature
d) Principal focus
Explanation: The point at which the principal axis intersects, the two refracting surfaces are front vertex and back vertex. Focal length is the distance of focal point and optical centre. The length of radius of curvature of the surface, is called radius of curvature. The point at which converging and diverging of the rays take place is called principal focus.
8. What is the power of lens?
a) Reciprocal of R
b) Reciprocal of C
c) Reciprocal of f
d) Equal to f
Explanation: The reciprocal of focal length is power.
i.e., P=1/f
while, the reciprocal of length of radius of curvature is called curvature.
i.e., C=1/R.
9. If the object is at infinity, where and how will the image form?
a) At 2F, real, inverted and of same size
b) At F, point size, real and inverted
c) Between F and 2F, real, inverted and diminished
d) Beyond 2F, real, inverted and magnified
Explanation: When the object is at infinity, the image will form at F. It will be of point size, real and inverted. Whereas, if the object is at 2F, the image will form at 2F and the image will be real, inverted and of the same size. Moreover, if the object is beyond 2F, the image will form, in between F and 2F, it will be real, inverted and diminished. While, if the object is in between F and 2F, the image will form beyond 2F, it will be real, inverted and magnified.
10. If the lens is placed in water, then the refractive index with respect to water will be ________
a) m=a/b
b) m=b/a
c) m*a=b
d) m/b=a
Explanation: The refractive index of glass with respect to water, “m” is:
m=a/b
where, “m” is the refractive index of glass with respect to water, “a” is the refractive index of glass and “b” is the refractive index of water.
whereas, the refractive index of water with respect to glass, “n” (say) is:
n=b/a
=> n*a=b