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

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

virtual and of same size

virtual image is not formed

virtual and diminished

virtual and magnified

#2. 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.

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

Concave mirror

Plane mirror

Concave lens

Convex mirror

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

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

at f

at 2f

between O and f

beyond 2f

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

a convex mirror

a plane 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.

#6. 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.

#7. A light ray enters from medium A to medium B as shown in figure. The refractive index of medium B relative to A will be

greater than unity

zero

equal to unity

less than unity

(a) Here, ∠i = 60°, ∠r = 45°

Using Snell’s law of refraction, refractive index of medium B with respect to medium A.

n=sin i / sin r

=> sin 60 / sin 45

=> √3/√2

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

negative

positive

neither positive nor negative

positive or negative depending on the size of the object

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

focus

optical centre

radius of curvature

centre of curvature

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

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

+50 cm

-50 cm

-100 cm

+100 cm

#11. 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

goes straight into the second medium

does not enter at all

bends away from the normal

bends towards the normal

#12. 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

#13. 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.

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

real and erect

virtual and inverted

real and inverted

virtual and erect

#15. 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

25 cm

60 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.

#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

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

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

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

As c> v so µ>1

#17. Focal length of a concave mirror is

depends on the position of image

depends on the position of object

positive

negative

#18. 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

25 cm

40 cm

At infinity

10 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

#19. 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.

#20. 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

between focus and centre of curvature

at the centre of curvature

at the focus

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

#21. 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.

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

Concave mirror only

Convex mirror only

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

Convex lens 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.

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

Combination of convex and concave mirror

Plane mirror

Concave mirror

Convex mirror

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

#24. 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 focus

at infinity

at the pole

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

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

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

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

#26. 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

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

both (2) and (3)

decreased velocity

decreased wavelength

increased velocity

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

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

is less than one

is equal to one

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

is more than one

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.

#29. A divergent lens will produce

always real image

none of these

always virtual image

both real and virtual image

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

#30. 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

– 60 cm

– 30 cm

– 40 cm

– 20 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

#31. 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.

#32. Magnifying power of a concave lens is

always < 1

can have any value

always > 1

always = 1

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

45°

0°

90°

depend on the material of the slab

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

#34. 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

Prism

Convex lens

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.

#35. The laws of reflection hold good for

plane mirror only

convex mirror only

concave mirror only

all mirrors irrespective of their shape

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

#36. 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

both concave

the mirror is convex and the lens is concave

the mirror is concave and the lens is convex

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

between F and 2F

only (1) and (2) both

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.

#38. 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 rectangular glass slab

A convex lens

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.

#39. 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

virtual, upright and enlarged

real, inverted and enlarged

real, inverted and diminished

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

#40. 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 horse of less brightness

a horse of black stripes

a zebra of black stripes

a zebra 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.

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