Q). An object placed at a distance of 30 cm in front of a concave mirror of focal length 20 cm. The image is formed at a distance of
A) 60 cm
B) -60 cm
C) 30 cm
D) -30 cm
Q). Every lens has _________ focal points.
A) one
B) two
C) three
D) infinite
Q). The radii curvatures of a double convex lens are 10 cm and 10 cm. Its refractive index is 1.5. The focal length is
A) 10 cm
B) 0.1 cm
C) 100 cm
D) zero
Explanation: R1 = 10, R2 = 10, n = μ = 1.5
∴ 1/f =
= 0.5 x[2/10] = 5/10×2/10 = 10/100 = 1/10 cm
F = 10 cm, f = 4, so image forms infinity
Q). An object is placed 10 cm from a converging lens of focal length 10 cm. The image is formed at a distance of
A) 10 cm
B) 20 cm
C) 100 cm
D) ∞
Q). A convex lens is placed in water. The focal length will
A) remain same
B) decrease
C) increase
D) none of the above
Q). A light ray incident on curved surface travelling from rarer medium to denser medium bends _______ the normal.
A) towards
B) away from
C) parallel to
D) none
Q). Which part of human eye is called variable aperture?
A) Retina
B) Cornea
C) Pupil
D) Lens
Q). In case of eye defect called ‘myopia’ image forms
A) after retina
B) before retina
C) on retina
D) none of the above
Q). In prism experiment, the i-d curve looks like
A) straight line
B) circle
C) parabola
D) ellipse
Q). The splitting of white light into different colours is called
A) dispersion
B) scattering
C) refraction
D) reflection