CBSE X Science Natural Phenomenon - EducareHut (Next Gen Knowledge Point)

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#1. Light from the Sun falling on a convex lens will converge at a point called

optical centre

centre of curvature

focus

radius of curvature

Explanation: (b) The parallel ray coming from the sun, after refraction through the convex lens converge at its focus.

#2. A beam of light is incident through the holes on side A and emerges out of the hole on the other face of the box as shown in the figure. Which of the following could be inside the box?

Rectangular glass slab

Convex lens

Prism

Concave lens

Explanation: (d) From figure, it is clear that parallel rays converge at a point and emerges from face B. So convex lens would be possible inside the box.

#3. An object at a distance of 30 cm from a concave mirror gets its image at the same point. The focal length of the mirror is

– 15 cm

+15 cm

– 30 cm

30 cm

Explanation: (c) When object is placed at 2F, the image formed by concave mirror is also at 2F.
So 2F = -30 or F = -15 cm.

#4. A point object is placed at a distance of 20 cm from a convex mirror of focal length 20 cm. The image will form at:

behind the mirror

at the pole

at infinity

at focus

#5. If the power of a lens is – 2 D, what is its focal length?

-50 cm

+100 cm

+50 cm

-100 cm

#6. Focal length of a concave mirror is

depends on the position of object

positive

depends on the position of image

negative

#7. An object is placed at a distance of 0.25 m in front of a plane mirror. The distance between the object and image will be

1.0 m

0.125 m

0.25 m

0.5 m

Explanation: (c) Distance between object and image = 0.25 0.25 = 0.5 m

#8. The distance between the optical centre and point of convergence is called focal length in which of the following cases?

Explanation :(c) Parallel rays after refiracting meet at the focus of a convex lens.

#9. The image formed by a convex lens can be

virtual and of same size

virtual image is not formed

virtual and magnified

virtual and diminished

#10. A full length image of a distant tall building can definitely be seen by using

a plane mirror

a convex mirror

a concave mirror

both concave as well as plane mirror

Explanation: (b) Convex mirror has a wide field of view as it forms virtual, erect and diminished image. Hence, fall length of image of distance tall building can definitely be seen by using it.

#11. When light falls on a smooth polished surface, most of it

is refracted into the second medium

is scattered

is reflected in different directions

is reflected in the same direction

#12. If a man’s face is 25 cm in front of concave shaving mirror producing erect image 1.5 times the size of face, focal length of the mirror would be

75 cm

15 cm

60 cm

25 cm

Explanation: (a) In concave shaving mirror, virtual erect and large size image, behind the mirror is obtained, using

m=-v/u=> 1.5=-v/(-25)

V=75/2 Cm

Now for Mirror Formula

1/f=1/v 1/u = 1/(75/2) 1/(-25)=-1/75

So f= -75 Cm

Hence, focal length of concave mirror is 75 cm.

#13. A spherical mirror and a spherical lens each have a focal length of -10 cm. The mirror and the lens are likely to be

both convex

the mirror is concave and the lens is convex

the mirror is convex and the lens is concave

both concave

#14. An object at a distance of + 15 cm is slowly moved towards the pole of a convex mirror. The image will get

enlarge and virtual

shortened and real

enlarged and real

diminished and virtual

Explanation: (d) Convex mirror always formed virtual and diminished image.

#15. If an incident ray passes through the focus, the reflected ray will

pass through the pole

pass through the centre of curvature

be parallel to the principal axis

retrace its path

#16. The angle of incidence for a ray of light having zero reflection angle is

90°

30°

45°

Explanation: (a) For reflecting surface ∠i = ∠r

#17. The refractive index of water is 1.33. The speed of light in water will be

1.33 × 108 m/s

3 × 108 m/s

2.66 × 108 m/s

2.26 × 108 m/s

µ=c/v

V=c/ µ
V=(3×10⁸)/1.33=2.26×10⁸ m/s

#18. A magnified real image is formed by a convex lens when the object is at

only (1) and (2) both

between F and 2F

Explanation: (d) When object is at 2F, real inverted and same size image is formed by convex lens. So, according to question option (1) and (2) both are correct.

#19. A divergent lens will produce

none of these

always virtual image

always real image

both real and virtual image

Explanation:(b) Diverging (concave) lens will always forms a virtual, erect and diminished image.

#20. If the image is formed in front of the mirror, then the image distance will be

positive

neither positive nor negative

positive or negative depending on the size of the object

negative

#21. When the object is placed between f and 2f of a convex lens, the image formed is

beyond 2f

between O and f

at 2f

at f

#22. Figure shows a ray of light as it travels from medium A to medium B. Refractive index of the medium B relative to medium A is

#23. Which of the following statements is/are true?

A concave lens has 4 dioptre power having a focal length 0.25 m

A convex lens has 4 dioptre power having a focal length 0.25 m

A convex lens has -4 dioptre power having a focal length 0.25 m

A concave lens has – 4 dioptre having a focal 0.25 m

Explanation: (a) Positive sign with power and focal length indicates that the given lens is convex.
Also f = 1P=14 = 0.25m

#24. Which of the following mirror is used by a dentist to examine a small cavity?

Plane mirror

Combination of convex and concave mirror

Concave mirror

Convex mirror

Explanation: (c) Concave mirror forms erect and enlarged image when held close to the cavity.

#25. In torches, search lights and headlights of vehicles the bulb is placed

between the focus and centre of curvature of the reflector

very near to the focus of the reflector

between the pole and the focus of the reflector

at the centre of curvature of the reflector

Explanation: (b) When source of light is placed very near to the focus of the reflector, which are concave in shape, the reflected light becomes parallel to the principal axis.

#26. In which of the following, the image of an object placed at infinity will be highly diminished and point sized?

Concave mirror, convex mirror, concave lens and convex lens.

Concave mirror only

Convex lens only

Convex mirror only

Explanation: (d) The incident ray coming from the object placed at infinity will be parallel to the principal axis. When the parallel beam of light incident on a mirror or lens, irrespective of their nature, after reflection/refraction, will pass or appear to pass through their principal focus. Hence highly diminished and point size image will be formed at their focus.

#27. Magnification produced by a rear view mirror fitted in vehicles

is equal to one

is more than one

is less than one

can be more than or less than one depending upon the position of the object in front of it.

Explanation: (a) Convex mirror is used as rear view mirror and always forms virtual, erect and diminished image. So magnification produced by a rear view mirror is less than one.

#28. A student does the experiment on tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence. He can get a correct measure of the angle of incidence and the angle of emergence by following the labelling indicated in figure:

III

#29. Image formed by reflection from a plane mirror is

real and inverted

virtual and inverted

real and erect

virtual and erect

#30. The image formed by concave mirror is real, inverted and of the same size as that of the object. The position of object should be

beyond centre of curvature

at the focus

between focus and centre of curvature

at the centre of curvature

Explanation:(c) When object lies at C of a concave mirror, image is also formed at ‘C’ and having same size real and inverted.

#31. If the magnification produced by a lens has a negative value, the image will be

virtual and erect

virtual and inverted

real and erect

real and inverted

#32. The laws of reflection hold good for

convex mirror only

concave mirror only

all mirrors irrespective of their shape

plane mirror only

Explanation: (d) The laws of reflection hold good for light reflected from any smooth surface irrespective of their shapes.

#33. For a real object, which of the following can produce a real image?

Concave lens

Plane mirror

Concave mirror

Convex mirror

Explanation: (b) Only concave mirror can produces a real image for the any position of object between its focus and infinity.

#34. The path of a ray of light coming from air passing through a rectangular glass slab traced by four students are shown as A, B, C and D in figure. Which one of them is correct?

Explanation: (b) When a light ray is incident obliquely on one face of rectangular glass slab, the emergent ray will be parallel to the incident ray and shifted sideward slightly.

#35. The nature of image formed by a convex mirror when the object distance from the mirror is less than the distance between pole and focal point (F) of the mirror would be

virtual, upright and enlarged in size

real, inverted and enlarged in size

real, inverted and diminished in size

virtual, upright and diminished in size

Explanation: (c) Convex mirror always forms a virtual, erect diminished image irrespective of the position of object in front of it.

#36. A concave mirror of radius 30 cm is placed in water. It’s focal length in air and water differ by

Explanation: (d) The focal length of spherical mirror does not depends on the surrounding medium.

#37. Beams of light are incident through the holes A and B and emerge out of box through the holes C and D respectively as shown in the figure. Which of the following could be inside the box?

A concave lens

A convex lens

A rectangular glass slab

A prism

Explanation: (a) Figure shows that emergent ray are parallel to the incident ray and shifted side ward slightly. This can be done by the rectangular glass slab only.

#38. The nature of the image formed by concave mirror when the object is placed between the focus (F) and centre of curvature (C) of the mirror observed by us is

virtual, upright and enlarged

virtual, erect and smaller in size

real, inverted and diminished

real, inverted and enlarged

Explanation: (c) When object lies between C and F, the real, inverted and enlarged image is formed beyond C.

#39. When object moves closer to a concave lens the image by it shift

away from the lens on the same side of object

away from the lens on the other side of lens

toward the lens

first towards and then away from the lens

Explanation: (b) When object infinity, image is formed at the focus of concave lens of object is moved towards lens, the image is also moved from its focus towards lens and its size increase.

#40. When object moves closer to convex lens, the image formed by it shift

away from the lens

first towards and then away from the lens

towards the lens

first away and then towards the lens

Explanation: (a) As object moves from infinity towards optical centre of the convex lens image is shifted away from its focal point and towards infinity.

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