If combination of two convex lenses is each that if parallel rays enter the combination up, leaving the combination are also parallel then the distance between the lenses will be equal to:
(a) sum of their focal lengths (b) difference of their focal lengths
(c) sum of reciprocals of their focal lengths (d) difference of reciprocals of their focal lengths
Two convex lenses of the same focal length ƒ are kept touching each other. The focal length of the combination will be:
(a) ƒ (b) 0.5ƒ (c) 2ƒ (d) 2ƒ +2ƒ
The magnification M of the real images formed by a convex lens of focal length f, exceeds=1 when the object distance is:
(a) Greater than 2ƒ (b) Equal to 2ƒ (c) Less than ƒ (d) Less than 2ƒ but greater than ƒ
A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is: (a) -1.5 D (b) -6.5 D (c) +6.5 D (d) +6.6D
The nature of the image formed by a convex mirror is:
(a) Virtual (b) Real (c) diminished (d) Depends on the distance of object from mirror.
If the magnification of a convex lens is 4 and the image of an object is formed at a distance of 24 cm, then the object must be at a distance of: (a) 12 cm (b) 4 cm (c) 6 cm (d) 96 cm
An object 5 cm high is placed 1 m in front of a converging lens of focal length 1.5 m. The height of the image (in cm) will be:
(a) 0.5 (b) 15 (c) 5 (d) 1.5
The objective of the astronomical telescope will form an image which is:
(a) Virtual and magnified (b) real and magnified (c) real and diminished (d) none of these
To get higher magnification by a magnifying glass, the lens used should be of:
(a) Short focal length (b) less than 1m focal length (c) Large focal length (d) none of these
Ratio of focal length of the objective to the focal length of the eye piece is greater than one for:
(a) telescope (b) microscope (c) both telescope and microscope (d) neither telescope nor microscope
A convex lens with chromic aberration focuses a parallel beam of green light at a distance of 16 cm from it. Then a parallel beam of yellow light will focus at a distance of:
(a) more than 16cm (b) less than 16cm (c) equals to 16cm (d)N.O.T
A convex lens of focal length 40cm is used in combination with concave lens of focal length 25cm. The power of combination is: (a) -1.5D (b) 1.5D (c) 6.5D (d) -6.5D
An object is placed 25cm from a convex lens which has a focal length of 10cm. At what distance will the image be formed?
(a) 25cm (b) 16.67cm (c) 12.44cm (d) 13.44cm
Lens with a long focal length is: (a) thick (b) thin (c) Cannot be said (d) N.O.T
Real images formed by single convex lenses are always:
(a) on the same side of the lens as the object (b) inverted (c) erect (d) smaller than the object (e) larger than the object
A virtual image is formed by:
(a) a slide projector (b) a motion-picture projector (c) a duplicating camera (e) a simple magnifier
A converging lens gives divergent rays if: (a) p < f (b) q < f (c) p > f (d) q > f
Chromatic aberration is caused by: (a) reflection (b) dispersion (c) refraction (d)N.O.T
The magnifying power of a telescope is M, If the focal length of its eye lens is halved, the magnifying power will become
(a) M / 2 (b) 2 M (c) 3 M (d) 4 M
If tube length of astronomical telescope is 105 cm and magnifying power is 20 for normal setting, calculate the focal length of objective (a) 100 cm (b) 10 cm (c) 20 cm (d) 25 cm
Focal length of a convex lens will be maximum for
(a) Blue light (b) Yellow light (c) Green light (d) Red light
The focal length of convex lens is 30 cm and the size of image is quarter of the object, then the object distance is
(a) 150 cm (b) 60 cm (c) 30 cm (d) 40 cm
Two lenses of power 6D and – 2D are combined to form a single lens. The focal length of this lens will be
(a)3/2m (b) 1/4m (c) 4 m (d)1/8m
If a lens is cut into two pieces perpendicular to the principal axis and only one part is used, the intensity of the image
(a) Remains same (b)1/2times(c) 2 times (d) Infinite
The combination of a convex lens (f = 18 cm) and a thin concave lens (f = 9 cm) is
(a) A concave lens (f = 18 cm) (b) A convex lens (f = 18 cm)
(c) A convex lens (f = 6 cm) (d) A concave lens (f = 6 cm)
Answers
Explanation:
) M / 2 (b) 2 M (c) 3 M (d) 4 M
If tube length of astronomical telescope is 105 cm and magnifying power is 20 for normal setting, calculate the focal length of objective (a) 100 cm (b) 10 cm (c) 20 cm (d) 25 cm
Focal length of a convex lens will be maximum for
(a) Blue light (b) Yellow light (c) Green light (d) Red light
The focal length of convex lens is 30 cm and the size of image is quarter of the object, then the object distance is
(a) 150 cm (b) 60 cm (c) 30 cm (d) 40 cm
Two lenses of power 6D and – 2D are combined to form a single lens. The focal length of this lens will be
(a)3/2m (b) 1/4m (c) 4 m (d)1/8m
If a lens is cut into two pieces perpendicular to the principal axis and only one part is used, the intensity of the image
(a) Remains same (b)1/2times(c) 2 times (d) Infinite
The combination of a convex lens (f = 18 cm) and a thin concave lens (f = 9 cm) is
(a) A concave lens (f = 18 cm) (b) A convex lens (f = 18 cm)
(c) A convex lens (f = 6 cm) (d) A concave lens (f = 6 cm)
Answer:
If combination of two convex lenses is each that if parallel rays enter the combination up, leaving the combination are also parallel then the distance between the lenses will be equal to:
(a) sum of their focal lengths (b) difference of their focal lengths
(c) sum of reciprocals of their focal lengths (d) difference of reciprocals of their focal lengths