1. Radius of curvature of the curvature of a convex mirror is 20 cm, and its focal length is:




... Answer is (c) -10 cm
For convex mirror f = -`\frac {R}{2}` = -10 cm{from the book]. The negative sign is due to the centre of curvature lying on the opposite side of the reflecting surface of the convex mirror. [ But according to new Cartesian convention the focal length lies on the right side of the convex mirror and any distance on the right side has a Positive Sign (+ve) ]


2. Incident ray of light makes an angle of 30° with a plane mirror. What is the angle of reflection of a light ray?




... Answer is (a) 30°
For a plane mirror the angle of incident of light ray = angle of reflection


3. Focal length of the concave lens is




... Answer is (b) negative
A concave lens is a diverging lens and will always have a negative focal length.


4. A virtual, erect, and smaller than an object, image is always formed by _____________




... Answer is (d) Convex mirror
The image formed by a convex mirror is always virtual and erect. When an object is placed at infinity, a virtual image is formed at focus and the size of the image is smaller

.


5. A denser medium has a refractive index of 1.5 the critical angle for it is:




... Answer is (a) 41.8°
C = `\sin⁻¹frac {1}{n}` = `\sin⁻¹frac {1}{1.5}` = sin⁻¹ (0.667) = 41.8°


6. Concave lens forms virtual, erect, and enlarges the image if the object is placed




... Answer is (d) Between F and C
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7. A concave lens has a focal length of 5 cm. Find its power? :




... Answer is (a) 20 D
P = `\frac {1}{f}`


8. A magnifying glass has a focal length of 5 cm then its magnifying power is:




... Answer is (b) 6
Since magnifying glass is used for magnifying near objects So `\m_θ` = `\frac {N}{f}` + 1 where near point N = 25 cm. Thus `\m_θ` = `\frac {25 cm}{5 cm}` + 1 = 6


9. . Near the point of a person lies 40 cm from him. He is suffering from :




... Answer is (a) Farsightedness
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10. Accommodation in the eye is done by:




... Answer is (c) Ciliary Muscle
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