#### 12th Standard Physics English Medium Ray Optics Reduced Syllabus Important Questions 2021

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 105
Multiple Choice Questions
15 x 1 = 15
1. The speed of light in an isotropic medium depends on,

(a)

its intensity

(b)

its wavelength

(c)

the nature of propagation

(d)

the motion of the source w.r.t medium

2. When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index,

(a)

less than one

(b)

less than that of glass

(c)

greater than that of glass

(d)

equal to that of glass

3. A ray of light travelling in a transparent medium of refractive index n falls, on a surface separating the medium from air at an angle of incidents of 45o. The ray can undergo total internal reflection for the following n,

(a)

n = 1.25

(b)

n = 1.33

(c)

n = 1.4

(d)

n= 1.5

4. The light reflected by plane mirror may form a real images.

(a)

If the rays incident on the mirror are diverging

(b)

If the rays incident on the mirror are converging

(c)

If the object is placed very close to mirror

(d)

Under no circumstance

5. Ray optics is valid, when characteristic dimensions are

(a)

of the same order as the wave length oflight

(b)

much smaller then the wavelength of light

(c)

of the order of one millimeter

(d)

much larger than the wavelength oflight

6. A man having height 6 m, want to see full height in mirror. They observe image of 2 m height erect, then used mirror is

(a)

Concave

(b)

convex

(c)

plane

(d)

none of these

7. A point object is placed at a distance of 30 cm from a convex mirror of focal length 30 cm, The image will from at

(a)

Infinity behind the mirror

(b)

Focus

(c)

Pole

(d)

15 cm

8. A concave mirror of focal length 15 cm forms an image having twice linear dimensions of the object. The position of the object when the image is virtual will be

(a)

22.5 cm

(b)

7.5 cm

(c)

7.5 cm

(d)

45 cm

9. A convex mirror has a focal length f. A real object is placed ata distance Jinfront the pole produces an image at

(a)

infinity

(b)

f

(c)

$\cfrac { f }{ 2 }$

(d)

2f

10. All of the following statement are correct except

(a)

The magnification produced by a convex mirror is always less than one

(b)

A virtual, erect same sized image can be obtained using a plane mirror

(c)

A virtual, erect magnified iinage can be formed using a concave mirror

(d)

A real, inverted, same-sized image can be formed using a convex mirror

11. A virtual image three times the size of the object is obtained with a concave mirror of radius of curvature 36 cm, The distance of the object from the mirror is

(a)

5 cm

(b)

12 cm

(c)

10 cm

(d)

20 cm

12. A dice is placed with its one edge parallel to the principal axis between the principal focus and the centre to the curvature of a concave mirror. Then the image has the shape of

(a)

Cube

(b)

Cuboid

(c)

Barrel shaped

(d)

Spherical

13. A luminous object is placed 20 cm from surface of a convex mirror and a plane mirror is set so that virtual images formed in two mirrors coincide. If plane ~irror is at a distance of 12 cm from object. Then focal length of convex mirror, is

(a)

5 cm.

(b)

10 cm

(c)

20 cm

(d)

40 cm

14. A cube of side 2m is placed in front of a concave mirror focal length 1m with its face P at a distance of 3m and face Q at a distance of 5m from the mirror. The distance between the images of face P and Q and height of images P and Q are

(a)

1m, O.5m,0.25m

(b)

0.5m, 1m, 0.25m

(c)

0.5 m, 0.25m, 1m

(d)

0.025m, 1m, 0.5m

15. A concave mirror forms an image of sun at a .distance of 12 ern from it

(a)

The radius of curvature of this mirror is 6 cm

(b)

To use it as a shaving mirror, it must be held at a distance of 8 - 10 cm from the face

(c)

If an object is kept at a distance of 12 cm from it, the image formed will be same size as the object

(d)

All the above

16. 2 marks
10 x 2 = 20
17. What is critical angle and total internal reflection?

18. Arrive at lens equation from lens maker's formula.

19. What is Rayleigh's criterion?

20. What type of lens is formed by a bubble inside water?

21. When a wave undergoes reflection at a denser medium, what happens to its phase?

22. What is meant by focal plane?

23. What is simultaneous reflection?

24. Define angle of deviation d.

25. A convex lens (n = 1.5) of focal length fs immersed
(I) in water n = 1.33 and
(ii) in carbon disulphide n = 1.6, how does the lens behave in the two cases?

26. A ray of light incident on a concave lens becomes parallel to the principal axis after refraction.Show this situation with the help of a ray diagram.

27. 3 Marks
10 x 3 = 30
28. Describe the Fizeau's method to determine speed of light.

29. Obtain the equation for radius of illumination (or) Snell's window.

30. Derive the equation for angle of deviation produced by a prism and thus obtain the equation for refractive-index of material of the prism.

31. Prove that when a reflecting surface of light is tilted by an angle θ, the reflected light will be tilted by an angle 2θ.

32. Light travels from air in to glass slab of thickness 50 cm and refractive index 1.5.
(i) What is the speed of light in glass?
(ii) What is the time taken by the light to travel through the glass slab?
(iii) What is the optical path of the glass slab?

33. Locate the image of the point object O in the situation shown. The point C denotes the centre of curvature of the separating surface

34. Determine the focal length of the lens made up of a material of refractive index 1.52 as shown in the diagram. (Points C1 and C2 are the centers of curvature of the first and second surface.)

35. If the focal length is 150 cm for a glass lens, what is the power of the lens?

36. Light ray falls at normal incidence on the first face of an equilateral prism and emerges gracing the second face. What is the angle of deviation? What is the refractive index of the material of the prism?

37. What is focus (or) focal point of a mirror?

38. 5 Marks
8 x 5 = 40
39. A thin converging glass lens made of glass with refractive index 1.5 has a power of + 50D. When -this lens is immersed in a liquid of refractive index n, it acts as a divergent lens of focal length 100 cm. What must be the value of n?

40. Calculate the distance for which ray optics is good approximation for an aperture of 5 mm and wavelength 500 nm.

41. A diffraction grating consisting of 4000 slits per centimeter is illuminated with a monochromatic light that produces the second order diffraction at an angle of 30°. What is the wavelength of the light used?

42. What is the angle at which a glass plate of refractive index 1.65 is to be kept with respect to the horizontal surface so that an unpolarised light travelling horizontal after reflection from the glass plate is found to be plane polarised?

43. A ray of light falls on a transparent sphere with centre C as shown in the figure. The ray emerges from the sphere paralled to the line AB. Find the angle of refraction at A if refraction index of the material of the sphere is $\sqrt { 3 }$

44. A ray of light passes through an equilateral glass prism such that the angle of incidence is equal to the angle of emergence. The angle of emergence is $\cfrac { 3 }{ 4 }$ times the angle of prism. Calculate the refractive index of the glass prism.

45. Calculate the angle of dispersion between red and violet colours produced by a flint glass prism of refracting angle of 600• Given μ1=1.633 and = μr 1.622.

46. A convex lens, of focal length 20 cm, has a point object placed on its principal axis at distance of 40 cm from it. A plane mirror is placed 30 cm behind the convex lens. Locate the position' of image formed by this combination.