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

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

first towards and then away from the lens

away from the lens on the same side of object

away from the lens on the other side of lens

toward 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.

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

Convex lens only

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

Concave mirror 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.

#3. You are given three media A, B and C of refractive index 1.33, 1.65 and 1.46. The medium in which the light will travel fastest is

equal in all three media

The lower the refractive index, the faster the velocity of light.light will travel faster in a medium having lower refractive index.

#4. 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 diminished in size

real, inverted and enlarged in size

real, inverted and diminished in size

virtual, upright and enlarged in size

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

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

towards the lens

first away and then towards the lens

away from the lens

first towards and then away from 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.

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

real and erect

virtual and erect

real and inverted

virtual and inverted

#7. A10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is

– 40 cm

– 20 cm

– 30 cm

– 60 cm

Explanation: (b) Given

h0 = 10 mm = 0.1 cm

h2 = – 5 mm = -0.5 cm

for real image, v = – 30 cm

M=h_i/h_o= -v/u

1/f=1/v 1/u = 1/(-30) 1/(-60)

1/f= (-2-1)/60
=> 1/f= -1/20
F=-20 Cm

#8. 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 prism

A convex lens

A rectangular glass slab

A concave lens

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.

#9. 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.

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

beyond 2f

at 2f

at f

between O and f

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

3 × 108 m/s

1.33 × 108 m/s

2.26 × 108 m/s

2.66 × 108 m/s

µ=c/v

V=c/ µ
V=(3×10⁸)/1.33=2.26×10⁸ m/s

#12. As light travels from a rarer to a denser medium it will have

increased velocity

both (2) and (3)

decreased velocity

decreased wavelength

Explanation: (d) When light ray travel from rarer to denser medium, its velocity and wavelength both decrease as v = vλ.

#13. 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

between focus and centre of curvature

at the focus

at the centre of curvature

beyond 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.

#14. A concave mirror of focal length 20 cm forms an image having twice the size of object. For the virtual position of object, the position of object will be at

10 cm

40 cm

At infinity

25 cm

Explanation: (c) For virtual image,

M=-v/u = 2 => v=-2u

As 1/u=1/v 1/f

So 1/u 1/(-2u)=1/(-20)

1/2u=1/(-20)
U=-10cm

#15. 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

#16. The refractive index of transparent medium is greater than one because

Speed of light in vacuum < speed of light in transparent medium

Speed flight in vacuum = speed of light in transparent medium

Frequency of light wave changes when it moves from rarer to denser medium

Speed of light in vacuum > speed of light in transparent medium

µ=speed of light in Vacuum (c)/speed of light in medium(v)

As c> v so µ>1

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

is reflected in different directions

is reflected in the same direction

is refracted into the second medium

is scattered

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

is equal to one

is less than one

is more 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.

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

45°

30°

90°

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

#20. 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

diminished and virtual

enlarged and real

shortened and real

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

#21. A ray of light is travelling from a rarer medium to a denser medium. While entering the denser medium at the point of incidence, it

bends away from the normal

does not enter at all

goes straight into the second medium

bends towards the normal

#22. 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, erect and smaller in size

real, inverted and diminished

real, inverted and enlarged

virtual, upright and enlarged

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

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

retrace its path

pass through the pole

be parallel to the principal axis

pass through the centre of curvature

#24. The angle of incidence i and refraction r are equal in a transparent slab when the value of i is

depend on the material of the slab

45°

0°

90°

Explanation: (a) When the incident ray falls normally on the glass slab, it will refracted without deviation, i.e. along the normal in the glass slab. So, ∠i = ∠r = 0

#25. 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?

Prism

Concave lens

Convex lens

Rectangular glass slab

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.

#26. 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.

#27. Large number of thin stripes of black paint are made on the surface of a convex lens of focal length 20 cm to catch the image of a white horse. The image will be

a zebra of black stripes

a zebra of less brightness

a horse of black stripes

a horse of less brightness

Explanation: (c) Complete image of the white horse is formed but of less intensity, the light falling on the curved portion will not react at the image position.

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

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

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

A concave lens has 4 dioptre power having a focal length 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

#29. 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.

#30. 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:

at focus

at the pole

behind the mirror

at infinity

#31. A divergent lens will produce

none of these

both real and virtual image

always virtual image

always real image

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

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

virtual and of same size

virtual and magnified

virtual image is not formed

virtual and diminished

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

neither positive nor negative

positive or negative depending on the size of the object

negative

positive

#34. 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

0.5 m

0.25 m

0.125 m

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

#35. The laws of reflection hold good for

all mirrors irrespective of their shape

plane mirror only

convex mirror only

concave mirror only

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

#36. Focal length of a concave mirror is

depends on the position of image

depends on the position of object

negative

positive

#37. 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.

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

+50 cm

+100 cm

-100 cm

-50 cm

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

real and erect

virtual and inverted

real and inverted

virtual and erect

#40. 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

30 cm

– 15 cm

+15 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.

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