Model Test Paper മാതൃകാ ചോദ്യപേപ്പർ
A full paper in the Kerala Class 9 Physics pattern for this chapter, covering the whole of “Refraction of Light” – optical density and refractive index, the rules of refraction, the glass slab, everyday and atmospheric refraction, critical angle and total internal reflection, and its uses. Several questions ask you to draw ray diagrams. Work on paper with a timer before you look at the solutions.
Standard IX · Physics
Chapter 1 · പ്രകാശത്തിന്റെ അപവർത്തനം · Refraction of Light
- The first 15 minutes are cool-off time: read every question and plan your answers; do not write.
- Answer all questions. Marks for each question are shown on the right.
- Draw ray diagrams neatly in pencil with a ruler. Show the normal as a dashed line and arrows on every ray. Measure all angles from the normal.
- For numericals write Given → Formula → Substitution → Answer. Take c = 3 × 108 m/s.
SECTION AAnswer all · 8 × 1 = 8 marks
1.
The ratio of the speed of light in vacuum to the speed of light in a medium is called the of that medium.
(1)2.
Which of these media has the highest optical density?
(1)(a) air(b) water(c) glass(d) diamond
3.
The critical angle of glass is 42°. Inside a glass block, total internal reflection takes place when the angle of incidence is
(1)(a) 30°(b) 40°(c) 42°(d) 50°
4.
A ray of light falls perpendicularly on the surface of a glass slab. Its angle of refraction is .
(1)5.
Find the relation and fill in: air → water : bends towards the normal :: water → air :
(1)6.
The twinkling of stars is due to .
(1)7.
The unit of refractive index is
(1)(a) m/s(b) s/m(c) metre(d) it has no unit
8.
The 2009 Nobel Prize in Physics for achievements in the transmission of light through optical fibres went to .
(1)SECTION BAnswer all · 5 × 2 = 10 marks
9.
Light travels through glycerine at a speed of 2.04 × 108 m/s. Find the refractive index of glycerine. (Speed of light in vacuum c = 3 × 108 m/s)
(2)10.
A ray of light passes obliquely from air into water (figure). (a) Complete the diagram showing the refracted ray and mark the angle of incidence i and the angle of refraction r. (b) Which is greater, i or r?
(2)11.
Write the two conditions necessary for total internal reflection.
(2)12.
A boy fishing with a bow and arrow in a paddy-field canal aims a little below the place where he sees the fish. Why? Explain with the help of the figure.
(2)13.
Write two differences between reflection from a plane mirror and total internal reflection.
(2)SECTION CAnswer all · 4 × 3 = 12 marks
14.
The speed of light in three media P, Q and R is given below.
(a) Find the refractive index of Q (c = 3 × 108 m/s). (b) Which medium is optically the densest? (c) A ray passes obliquely from R into P. Does it bend towards or away from the normal? Why?
(3)| Medium | P | Q | R |
|---|---|---|---|
| Speed of light (m/s) | 2.25 × 108 | 1.25 × 108 | 2 × 108 |
15.
A ray of light inside a semicircular glass block is aimed at the centre of its flat face at three different angles of incidence: (i) 35° (ii) 42° (iii) 50°. In (i) the angle of refraction in air is 60°. (a) What happens to the ray in (ii)? What is this angle called? (b) What happens in (iii)? Name the phenomenon. (c) Why does the ray in (i) bend away from the normal?
(3)16.
A ray of light PQ falls on a rectangular glass slab ABCD at Q with an angle of incidence of 50° (figure). (a) At which points does refraction take place? (b) Draw the path of the ray through the slab and out of it. (c) How is the emergent ray related to the incident ray PQ?
(3)17.
On a hot summer afternoon the road far ahead appears wet, but there is no water when we reach the spot. (a) Name this phenomenon. (b) Explain how it happens. (c) Why is the image seen upside down?
(3)SECTION DAnswer all · 2 × 5 = 10 marks
18.
Refractive indices of some media are given below.
(a) In which medium is the speed of light the highest? (b) Find the speed of light in diamond (c = 3 × 108 m/s). (c) A ray passes obliquely from kerosene into water. Does it bend towards or away from the normal? Why? (d) The critical angle of diamond is 24.4° and that of glass is 42°. Which of the two sparkles more? Explain.
(5)| Medium | water | kerosene | crown glass | diamond |
|---|---|---|---|---|
| Refractive index | 1.33 | 1.44 | 1.52 | 2.42 |
19.
Right-angled isosceles glass prisms (critical angle 42°) are used in cycle reflectors and in periscopes. (a) A ray falls normally on the face PQ of a reflector prism (figure). Draw its path and write the angle at which it strikes the other two faces. (b) Why is the ray totally reflected at those faces? (c) In which direction does the ray finally leave the prism, and why is this useful on a cycle? (d) In a prism periscope, through what angle does each prism turn the light? (e) If the prisms of a periscope were hollow and filled with water (critical angle 48.6°), would the periscope work? Why?
(5)