1Which of the following rules applies during the refraction of light? (i) Light bends only while passing from a rarer medium to a denser medium. (ii) Light bends towards the normal as it passes from a denser medium to a rarer medium. (iii) When light passes from a rarer medium to a denser medium, the angle of incidence is smaller than the angle of refraction. (iv) The angle of refraction becomes greater than the angle of incidence when light travels from a denser medium to a rarer medium.
2A ray of light passes from medium 1 into medium 2. In medium 1 it makes an angle of 15° with the normal, and in medium 2 the refracted ray makes an angle of 30° with the normal. Which statement is correct? (i) Medium 2 is denser and medium 1 is rarer. (ii) The speed of light in medium 2 is less than in medium 1. (iii) The speed of light in medium 1 is twice that in medium 2. (iv) Medium 1 is denser and medium 2 is rarer.
3A ray passes through a rectangular glass slab. Four quantities are marked by numbers: number 2 is outside the slab at the top face, between the ray arriving and the normal; number 4 is inside the slab just below the top face, between the ray and the normal; number 1 is outside the slab at the bottom face, between the ray leaving and the normal; number 3 is the perpendicular gap between the ray leaving and the dotted extension of the ray that arrived. Which naming is correct? (i) 1 angle of incidence, 2 angle of refraction, 3 lateral shift, 4 angle of emergence. (ii) 1 angle of emergence, 2 angle of incidence, 3 lateral shift, 4 angle of refraction. (iii) 1 angle of refraction, 2 angle of emergence, 3 lateral shift, 4 angle of incidence. (iv) 1 lateral shift, 2 angle of refraction, 3 angle of incidence, 4 angle of emergence.
4Which of the following is the result obtained from observing refraction through a glass slab? (i) ∠i = ∠e < ∠r (ii) ∠i > ∠r = ∠e (iii) ∠i < ∠e = ∠r (iv) ∠i = ∠e > ∠r
5What is the value of the critical angle of glass? (i) 42° (ii) 49° (iii) 24° (iv) 48°
6Among endoscopes, spectacles, mirages, dispersion of light, rainbows, optical fibres and hand lenses, in which instruments and processes does total internal reflection of light take place? (i) endoscope, spectacles and mirage (ii) dispersion of light, rainbow and hand lens (iii) rainbow, optical fibre and mirage (iv) endoscope, mirage and optical fibre
7The velocities of green, violet and red light in a prism during dispersion are \( v_g \), \( v_v \) and \( v_r \). Which relation is correct? (i) \( v_g > v_v > v_r \) (ii) \( v_g > v_v < v_r \) (iii) \( v_g < v_r < v_v \) (iv) \( v_g > v_r < v_v \)
8An object AB stands on the principal axis of a convex lens, between the principal focus F1 and the lens. What are the characteristics of its image? (i) virtual, erect, magnified (ii) real, inverted, diminished (iii) real, erect, magnified (iv) virtual, inverted, inverted
9Choose the correct statement about images formed by concave and convex lenses. (i) A convex lens forms a real, inverted and diminished image of an object. (ii) A concave lens forms a virtual, erect and diminished image of an object. (iii) A convex lens forms a real, inverted and magnified image of an object. (iv) A concave lens forms a virtual, erect and magnified image of an object.
10What is the correct understanding of eye problems and their causes? (i) When the lens of the eye becomes cloudy, colour blindness occurs. (ii) When the focal length of the eye lens increases, shortsightedness occurs. (iii) When the shape of the surface of the cornea changes, a defect in vision is seen. (iv) Night blindness occurs due to weakness of the cone cells of the retina.
11Differentiate between reflection of light and total internal reflection of light.
12Differentiate between a concave lens and a convex lens.
13Differentiate between the near point and the far point of the eye.
14Differentiate between shortsightedness and longsightedness.
15Differentiate between colour blindness and night blindness.
16Give reason: between glass and water, glass is considered the denser medium and water the rarer medium.
17Give reason: when a coin is placed in a glass containing water, it appears to rise a bit.
18Give reason: when letters written on paper are seen from the top of a glass slab, they appear slightly raised.
19Give reason: stars twinkle.
20Give reason: the sun appears on the horizon about two minutes before the actual sunrise.
21Give reason: a diamond appears to shine but a piece of glass cut to the same shape does not.
22Give reason: sunlight is refracted when it is passed through a prism.
23Give reason: a convex lens converges light rays.
24Give reason: a concave lens diverges the rays of light.
25Give reason: deficiency of vitamin A in the body is one of the main causes of night blindness.
26Give reason: colour blindness occurs when the cone cells of the retina stop functioning.
27What is the refraction of light?
28Write the laws of refraction of light.
29A pencil is placed slanting in a vessel of water, so that half of it is under the water. What change is noticed in its shape? Explain with a ray diagram, and name the process.
30When a light ray passes from water to air, the angle of incidence and angle of refraction at the water-air boundary are 40.5° and 60°. Draw a ray diagram showing the refraction, and give the reason why an object outside appears farther away than its actual position to an observer inside the water.
31What is a critical angle?
32What is total internal reflection of light?
33Write two conditions necessary for total internal reflection of light.
34Data can now be transmitted very fast through fibre internet. Mention the role of total internal reflection of light in fibre internet.
35In endoscopy, colonoscopy and keyhole surgery, how is total internal reflection of light used in the devices that send light to internal organs of the human body without large incisions?
36What is dispersion of light?
37Mention the reason for the dispersion of light.
38Draw ray diagrams showing (i) refraction of light through a glass slab and (ii) dispersion of light through a prism.
39A person is curious to know why a rainbow always appears semicircular and of the same size. Explain, including the position of the sun, the position of the water droplets and the process of dispersion.
40Define these terms related to a lens: (i) centre of curvature (ii) optical centre (iii) principal axis (iv) focus.
41What is meant by the power of a lens?
42The powers of two convex lenses are +2 D and +4 D. (i) Which of them is thicker? Give reason. (ii) Calculate the focal length of each lens.
43In which case is the image formed by a convex lens real and of the same size as the object? Show the ray diagram.
44A man standing on a bank throws a spear at a fish he sees in the water. Will the spear hit the fish? Explain based on the real depth of the fish.
45A ray diagram shows light travelling along a curved, wavy tube, bouncing from wall to wall inside it. What process is shown? Name any two devices that work on this process.
46Complete these ray diagrams: (i) a ray AO in air strikes a water surface at O; (ii) a ray in water strikes the water-air surface at 48.8° to the normal; (iii) a ray enters a right-angled glass prism with angles 90°, 60° and 30°, perpendicular to one of the faces that form the right angle; (iv) a ray PQ strikes the long face AC of a glass prism ABC, which has a right angle at B and AB = BC, at 90°; (v) a ray of red light strikes one face of a triangular prism; (vi) an object is placed beyond 2F in front of a convex lens.
47Three uses of lenses are shown: a lens focusing sunlight on to a piece of paper until it burns, a hand lens held over printed text, and a man looking through a small viewer fitted in a door. Mention the facts, with ray diagrams, that apply to each use.
48A ray of white light passes through a triangular prism and splits. The ray bent more towards the base reaches point X on a screen, and the ray bent less reaches point Y above it. (a) Which colours are indicated by X and Y? (b) Why is Y bent less than X?
49How can the light dispersed by a prism be converted back into white light?
50The focal lengths of two lenses are 20 cm and -20 cm. Name the type of each lens. Which one forms a virtual and magnified image when an object is kept 16 cm away from it? Explain with a scaled ray diagram.
51Write the functions of these parts of the eye: (i) ciliary muscle (ii) cornea (iii) lens (iv) iris (v) pupil (vi) retina.
52Write any two problems that may be seen in corneal injury.
53A student in a classroom shifts his eyes from letters on the whiteboard to a distant object seen through the window. Explain the role of the ciliary muscles in changing the thickness of the eye lens.
54A ray diagram shows rays from a nearby object at the normal near point (25 cm) entering the eye and forming the image behind the retina. Identify the defect of vision. Write two causes and its correction.
55A student cannot read the letters on the whiteboard from the last bench but reads them clearly from the first bench. (i) What defect of vision does the student have? (ii) Draw a ray diagram of this defect. (iii) Write any two reasons for it. (iv) Explain, with a ray diagram, the role of the lens used to correct it.
56Explain, with a ray diagram, the role of the lens used to correct longsightedness.
57A student concludes that the defect of vision is greater in a person wearing spectacles with thick lenses than in one wearing thin lenses. Is this correct? Justify.
58Compare the use of spectacles and the use of contact lenses to correct visual defects.
59Explain the laser surgery method used to solve eyesight problems.
60What is a cataract? Write the role of the intraocular lens developed by Nepal's ophthalmologist Dr. Sanduk Ruit in the treatment of cataracts.
61The speeds of light in air and glass are \( 3 \times 10^8 \) m/s and \( 2 \times 10^8 \) m/s. Calculate the refractive index of glass with respect to air.
62The refractive index of a diamond is 2.42. If the speed of light in air is \( 3 \times 10^8 \) m/s, calculate the speed of light in a diamond.
63A ray of light falls on the surface of a plastic block. The angle of incidence and the angle of refraction are 45° and 33°. Calculate the refractive index of the plastic.
64Calculate the power of a lens having a focal length of 25 cm.
65The power of the lens in a student's spectacles is -6 D. Calculate its focal length and name the type of lens.
66Why does the maximum refraction in the eye take place at the cornea and not at the lens?
67Why should the eyes not be rubbed when dust or sand enters them during a storm?
68Why does keratoconus first cause shortsightedness?
69After the death of an eye donor, why are the eyelids closed, and why must the cornea be removed within 8 to 12 hours?
70What is corneal transplantation, who needs it, and what role does the Nepal Eye Bank play in it?