IMPORTANT QUESTIONS IN PHYSICS
1. (REFRACTION OF LIGHT)
1. What do you mean by refraction of light? Give examples of it?
2. Explain how light travels i) from a denser medium to rarer medium. ii) from a
rarer medium to a denser medium.
3. What is lens? How many types of lenses are there?
4. Write the differences between convex and concave lens.
5. Explain the image formation by a convex lens for various positions of the
object. And also draw the ray diagrams.
6. Explain the image formation by a concave lens for various positions of the
object. And also draw the ray diagrams.
7. If the image formed by a lens for all positions of the object placed in front of it
is always virtual, erect and diminished, state the type of the lens. Draw a ray
diagram in support of your answer.
8. Write the uses of Convex lens and Concave lens.
9. Write New Cartesian sign convention for spherical lenses.
10. Explain the rules of refraction (i. Parallel to principal axis ii. Passing through F
iii. Passing through optical centre ) in Convex lenses along with neat ray
diagrams.
11. Explain the rules of refraction (i. Parallel to principal axis ii. Directed towards
F and iii. Passing through optical centre ) in Concave lenses along with neat ray
diagrams.
12. Simple Numerical problems.( Solved problems in text book, exercise
problems and all problems discussed in class room).
13. Define and explain about refractive index of a medium.
14. Define and explain about power of a lens.
15. Briefly describe refraction through a rectangular slab.
16. Write and explain laws of refraction.
ANSWERS
1. Refraction of light: When light travels obliquely from one medium to
another,the direction of propagation changes in the second medium. This
phenomenon of light is known as refraction of light.
Examples: a) The bottom of a tank containing water appears to be raised.
b) A lemon kept in water in a glass tumbler appears to be larger than actual size.
c) A pencil partly immersed in water in a glass tumbler appears to be displaced ,
at the interface of air and water.
2. Refraction from denser to rarer medium : – When light rays pass from denser
to rarer medium, the light rays bend away from the normal. Due to this the angle of
refraction becomes more than the angle of incidence. e.g. In case when light rays
pass from water to air or glass to air, light rays bend away from the normal. The
speed of light rays becomes greater while passing from glass or water to air.
Refraction from rarer to denser medium: When light rays pass through rarer to
a denser medium, the light rays bend towards the normal. Due to this the angle of
refraction is smaller than the angle of incidence. e.g. In the case when light rays
pass from air to water or from air to glass, it bends towards normal. It is because of
the reason that the speed of light rays reduces while passing from air to glass or
water.
.
3.. A transparent material bound by two surfaces, of which one or both surfaces are
spherical is called the lens. There are two types of lenses:
i. Convex (Converging) lens- Convex lenses are thick in the middle and thinner at
the edges. A convex lens is also known as the converging lens because it converges
parallel light rays inwards to a point known as the focus.
ii. Concave (Diverging) lens- Concave lenses are flat in the middle and thicker at
the edges. The concave lens is also known as a diverging lens because it diverges
the parallel light rays outward from a point known as the focus.
4. Differences between convex and Concave lenses.:
Concave lens Convex Lens
A concave lens is thinner in the center Convex lenses are thicker at the center and
and thicker at the edges. thinner at their edges.
It has a virtual focus It has a real focus
It has a negative focal length. It has a positive focal length.
Also called diverging lenses, as they They are also called converging lenses, as they
diverge the incident parallel beam of converge the parallel beam of light that passes
light. through them.
They can form only virtual images. They can form both virtual and real images.
They can form only diminished They can form both enlarged and diminished
images. images.
5. Table no.9.4 ( page no.152) and ray diagrams.
6. Table no.9.5 (page no.153) and ray diagrams.
7. Irrespective of the position of object, on the principal axis, you will get an erect,
virtual image, diminished in size in between the focal point and optic centre for
concave lens. ( Figure no.9.17 (page no. 155)
8. Uses of Convex lens:
Convex lens is used in microscopes and magnifying glasses to subject all the
light to a specific point.
Convex lens is used as a camera lens in cameras as they focus light for a clean
picture.
Convex lens is used in the correction of hypermetropia.
Uses of Concave lens:
They're used in binoculars and telescopes.
They are used as peepholes in doors.
They're found in flashlights, cameras, and other electronic devices.
They are used in the correction od Myopia
9. Sign conventions:
All distances are measured from the optic centre..
Distances measured in the direction of incident rays are taken as positive while
in the direction opposite of incident rays are taken negative.
Distances above the principal axis are taken positive and below the principal axis
are taken negative.
10. Figure 9.13, 9.14 and 9.15 (page no.153 &154)
11. Figure 9.13, 9.14 and 9.15 (page no.153 &154)
