UNIT 10: WAVE
Multiple choice questions [1 mark each]
1.
What is the speed of light in vacuum?
a) 3×108
m/s b) 3×108
Km/s c) 3×108
cm/s d) 332m/s
2.
Which colour light has the lowest speed in a medium?
a) blue b) violet c) orange d) red
3.
Absorption of which ray causes hotness?
a) UV rays b) infrared rays c) X-ray d) gamma ray
4.
Which of the following is the best refracting
transparent medium?
a)
glycerine b) water c) glass d) alcohol
5.
Which of the following is the refracting index of
glass?
a) 1.33 b) 1.36 c) 1.47 d) 1.5
6.
What is the refractive index of cornea?
a) 1.346 b) 1.357 c) 1.376 d) 1.676
7.
What is the refractive power of cornea of eye?
a) 43 D b) 44 D c) 45 D d) 42 D
8.
For how many days can cornea be preserved in
Optisol-GS?
a) 7 days b) 9 days c) 12 days d) 14 days
9.
In which hospital there is eye bank in Nepal?
a) Nepal
eye hospital b)
Lumbini Eye Institute
c)
Tilganga Eye hospital d)
Both b and c
10. How long
does the cataract surgery take?
a) 15-20
minutes b) 20-30 minutes c) 30-45 minutes d) at least 1 hour
11. Who
discovered colour blindness?
a) Dr.
Sandook Rooit b) John Dalton c) Thomas Young d) William Thomson
12. Which of
the following formula can be used to calculate the power of a lens?
13. A student
sitting on the last bench can clearly see things written on the books but
cannot see letters written on the board distinctly. What defect does he/she
have?a) Far
sightedness b) short-sightedness c) colour blindness d) none of these
14. The part
of the eye that focuses light onto the retina is the:
(a) cornea (b) iris (c) lens (d) pupil
15. The retina
is a thin layer of tissue at the back of the eye that contains:
(a) rods
and cones (b) the lens (c) the cornea (d) the iris
16. Rods are
responsible for:
(a) color
vision (b) night vision (c) both a and b (d) None of
these
17. Cones are
responsible for:
(a) color
vision (b) night vision (c) both a and b (d) None of
these
18. The eye is
able to focus on objects at different distances by:
(a)
changing the shape of the lens
(b)
changing the size of the pupil
(c) both
changing the shape of the lens and changing the size of the pupil
(d)
neither changing the shape of the lens nor changing the size of the pupil
19. The eye is
able to adjust to different levels of light by:
(a)
changing the size of the pupil
(b)
changing the shape of the lens
(c) both
changing the size of the pupil and changing the shape of the lens
(d) neither changing the size of the pupil nor changing the shape of the lens
Answers:
1(a), 2(b), 3(b), 4(c), 5(d), 6(c), 7(a), 8(d), 9(c), 10(a), 11(b), 12(d), 13(b),
14(c), 15(a), 16(b), 17(a), 18(a), 19(a)
Very Short Answer type questions. [1 mark
each]
1.
What is wave?
Wave is the path of
energy that transfer from one point to another.
2.
Define refraction of
wave.
The process of bending
of wave when it passes from one medium to another.
3.
What is diffraction of
wave?
Diffraction is a
phenomenon that occurs when waves encounter an obstacle or pass through an
aperture and bend or spread out as they propagate.
4.
What is total internal
reflection?
When the angle of
incidence in the denser medium is more than the critical angle, the rays of
light passing from denser medium to rarer medium reflect back to the same
medium. This phenomenon is called total internal reflection.
5.
What is a denser medium?
The medium in which
light travels slower than the other medium is called denser medium.
6.
What is rare medium?
The medium in which
light travels comparatively faster is called rarer medium.
7.
What is the speed of
light in water?
The speed of light in
water is 2.25×108m/s.
8.
What is keratitis?
Keratitis is the
inflammation or infection of the cornea, which is the clear, dome-shaped
surface that covers the front of the eye.
9.
Define corneal edema?
Corneal edema is the
swelling of cornea due deposition of liquid between the layer of cornea.
10. Define keratoconus.
Keratoconus is the
defect of cornea in which the shape of cornea change into funnel shape which
may lead to blindness.
11. What is corneal donation?
Corneal donation, also
known as cornea transplantation, is a surgical procedure in which a damaged or
diseased cornea is replaced with a healthy cornea from a dead donor.
12. Name the solution in which cornea is preserved.
The solution in which
cornea is preserved is called Optisol-GS (graft Solution).
13. What is cataract?
Cataract is a defect
of vision in which a cloudy patches of protein is formed in the lens.
14. Who developed intra-ocular lens?
Dr. Sandook Rooit
developed intra-ocular lens.
15. What is colour blindness?
Colour blindness is a
defect of vision in which a person has trouble in identifying blue, green and
red colours.
16. What are the types of colour blindness?
The types of colour
blindness are monochromacy and dichromacy.
17. What type of colour blindness is monochromacy?
Monochromacy is a type
of color blindness in which people have no color vision at all. They see the
world in shades of gray, like a black-and-white television.
18. Define Night blindness.
Night blindness is the
defect of vision in which a person can see objects clearly during the day time
but cannot see things clearly at night or dim light.
19. What type of colour blindness is dichromacy?
Dichromacy is a type of
colour blindness in which people are lacking the vision of either of the red,
blue or green colour.
20. What is lens? How many types of lens are there?
A lens is a part of transparent glass bounded by
two spherical surfaces.
21. Define convex lens.
The lens which is thicker in the middle and
thinner at the edges is called convex lens.
22. What is concave lens?
The lens which is thinner in the middle and
thicker at the edges is called concave lens.
23. What is centre of curvature?
Centre of curvature of a lens is defined as the
centre of the spherical surface from which a lens is made.
24. What is principal axis?
Principal axis is an imaginary line that joins
both the centre of curvature of a lens.
25. Define principal focus?
Principal focus is defined as the point at which
the parallel rays of light after refraction through a lens meet or appears to
be meeting.
26. What is focal length?
The distance between optical centre and
principal focus is called focal length.
27. Define optical centre?
The geometrical centre of a lens is called
optical centre.
28. What is focusing?
Focusing is the process of adjusting the
distance between the lens and the screen to produce a sharp and clear image.
29. What is an image? Name two types of image formed by lenses.
When an object is placed in front of a lens,
light rays from the object fall on it and get refracted. The refracted rays
produce a picture of object on the screen which is called an image.
30. What is real image?
The image which is formed by the actual
intersection of rays of light and can be obtained on screen is called real
image.
31. What is meant by virtual image?
The image which is not formed by actual
intersection of the rays of light and cannot be obtained on the screen is
called virtual image.
32. Name the type of lens which forms a real image.
A convex lens generally forms real image.
33. Name the type of lens which forms a virtual image.
A concave lens forms a virtual image.
34. What is optical instrument?
The instruments which are used to produce image
of an object by lens or combination of lenses are called optical instruments.
35. Give two examples of optical instruments.
Microscope and Telescope are the examples of two
optical instruments.
36. What is meant by the defect of vision? Name its types.
The disorder of human eyes in which a person can
not see an object clearly is called defect of vision. Its types are
long-sightedness and short sightedness.
37. What is far sightedness?
Far-sightedness is a defect of vision in which a
person cannot see near object clearly but can see the distant object clearly.
38. What is myopia or Short sightedness?
Myopia or short sightedness is a defect of
vision in which a person can see near objects clearly but cannot see distant
object clearly.
39. Write two cause of hypermetropia?
Two causes of hypermetropia are:
i)
the ciliary muscles fails to stretch the eye lens to required
thinness.
ii)
the contraction of eye ball.
40. Name two liquids found in the eye.
The names of two liquids found in the eye are:
i)
Aqueous humor
ii)
Vitreous humor
41. Write down the main causes of myopia.
The main causes of myopia are:
i)
the cilliary muscles fails to contract the eye lens to required
thickness.
ii)
the elongation of eye ball.
42. In which point the object should be kept in front of the convex
lens to have magnification one?
The object should be kept at 2F (center of
curvature) in front of the convex lens to have magnification one.
43.
What is near point of
the eye?
The near point of an eye is the nearest point
from the eye upto which the eye can see an object clearly.
44.
What is the near point
of a normal eye?
The near point of human eye is 25 cm from the
eye.
45.
What is far point?
The far point of an eye is the farthest point
from the eye upto which the human eye can see object clearly.
46. Define power of a lens.
The ability of a lens to
converge or diverge the rays of light passing through the lens is called the
power of lens.
Power of lens is also
defined as the reciprocal of focal length.
47. Write one function of cilliary muscles and iris?
The function of cilliary
muscles is to expand or contract the eye lens to required focal length and the
iris control the intensity of the light passing through the lens.
48. What is magnification of lens?
The ratio of the height
of the image to the height of the object is called magnification of lens.
It is also the ratio of
image distance to the object distance.
49. Write formula of power and magnification of lens.
1.
What type of lens is to
be used in spectacles to correct the short sightedness?
Concave lens is used in
the spectacles to correct the short sightedness.
2.
Write any function of
aqueous humour.
Aqueous humor is used to
retain the shape of eye ball.
3.
The power of lens is
+5D. Name the type of lens.
The power of lens is
+5D. The type of lens is convex lens.
4.
Sita is wearing
spectacles of power +2.5D. What is the defect in her eye?
Sita is wearing
spectacles of power+2.5 D. It means that she is suffering from long
sightedness.
Short Answer Question [2 marks each]
1.
Write any two rules of
refraction of light through lens.
Two rules of refraction of light are:
i)
A ray of light that passes parallel with the principal axis passes
through the principal focus after refraction.
ii)
A ray of light must pass through optical center without deviation.
2.
The incident light
deviates from its rectilinear path as it passes from one medium to another.
Give reason.
Different medium has
variable densities. When the incident light passes from one medium to another
there is a change in velocity due to the variation in densities. Thus, the
change in velocity makes light to deviate from its rectilinear path.
3.
What are the causes of
night blindness?
Night blindness is
causes by short-sightedness, cataracts, retinitis pigmentosa, genetic condition
and deficiency of vitamin A.
4.
What is meant by the
power of a lens? Write down the formula of SI unit.
The capacity of a lens
to converge or diverge light rays falling on it. Or it is the reciprocal of
focal length. Its formula is
P=1/focal length (m)
and its SI unit is Diopter (D).
5.
Write two differences
between convex lens and concave lens.
Two differences between
convex and concave lens are:
|
Convex lens |
Concave lens |
|
1. It is thicker in
middle and thinner at the edges 2. It always forms
real image except when the object is placed between F and O. |
1. It is thinner in
the middle and thicker at the edges. 2. It always forms a
virtual image. |
6.
Write two differences
between real image and virtual image.
Two differences between
real and virtual image are:
|
Real image |
Virtual image |
|
1. It is formed by the
actual intersection of refracted rays of light. 2. It can be obtained
on the screen. 3. It is always
inverted. |
1. It is formed by the
back trace of the refracted rays of light. 2. It cannot be
obtained on the screen. 3. It is always erect. |
7.
Write two differences
between image formed by convex lens and concave lens.
Two differences between
image formed by the convex and concave lens are:
|
Image formed by convex
lens |
Image formed by
concave lens |
|
1. Image is generally
real except when the object is placed between F and O. 2. Convex lens forms
enlarged image, diminished image or image of equal size depending on the
position of the object. |
1. Image is always
virtual. 2. Concave lens always
form diminished image where ever the object is placed. |
8.
Write two differences
between myopia and hypermetropia?
Two differences between
myopia and hypermetropia are:
|
Myopia (short sightedness) |
Hypermetropia (Long sightedness) |
|
1. In this defect, a person cannot see the distant object
clearly. 2. It is caused by the elongation of eye ball. 3. It can be correct by using concave lens of suitable focal
length. |
1. In this defect, a person cannot see the near object clearly. 2. It is caused by the contraction of eye ball. 3. It can be corrected by using convex lens of suitable focal
length. |
9.
What is meant by short
sightedness? Draw a neat diagram showing the type of defect .
Short sightedness is the
defect of vision in which a person's eye can see the near object clearly but
cannot see the distant object clearly.
The labeled diagram
showing the short sightedness:
1.
Which lens is used to
remove myopia? Why?
Concave lens is used to
remove myopia or short sightedness. This is because the parallel rays of light
coming from distant object first diverges concave lens and then converges by
eye lens. Due to the combined action of both the lenses the image is formed on
the retina and myopia is removed.
2.
Convex lens is called a
converging lens, why? Write with figure.
Convex lens is called
converging lens because it converges the parallel rays of light coming from
distant object at a point after refraction through it.
1.
Concave lens is called
diverging lens, why? Write with figure.
Concave lens is called
diverging lens because it diverges the parallel rays of light after refraction
through it.
2.
Long sightedness
(hypermetropia) can be removed by a convex lens, why?
Long-sightedness can be
removed by using spectacles containing convex lens. When a convex lens of
suitable focal length is used in front of eye lens, the rays of light coming
from nearby object are first converges by convex lens and then by eye lens.
Thus due to the combine effect of both the lenses, image of the object is
formed on retina and hence the person can see nearby object clearly.
3.
Why does rainbow appears
curved?
Rainbows appear curved
because the sunlight is refracted by the water droplets in the atmosphere. The
angle of refraction depends on the wavelength of the light, so the different
colors of light are bent by different amounts as they have different velocities
inside the water droplets. This is why we see a rainbow with a spectrum of
colors, with red on the outside and violet on the inside. This makes the
rainbow a curve shaped.
4.
The magnification is
more than one, what does it mean?
The magnification of a
lens is more than one, it means that the size of image is larger than that of
the object.
5.
Write two differences
between far point and near point.
Two differences between far point and near point are:
|
Far point |
Near Point |
|
1. It is the farthest distance at which a person's eye can see
an object clearly. |
1. It is the nearest distance at which a human eye can see a
nearest object clearly. |
|
2. It is infinity for a normal eye. |
2. It is 25 cm form the eye for a normal eye. |
6.
It is difficult to catch
a fish in water, why?
It is difficult to catch a fish in water
because of refraction of light. The rays of light coming from the fish bends
away from normal. For the observer outside the water, fish appear at apparent
position from the actual position of the fish. Thus, a man trying to catch the
fish put his/her hand at the apparent position.
7.
A clear pond seems
shallower than its real depth. Give reason.
It is known that water is a denser
medium and air is optically rarer medium. The rays of light coming from the
bottom of the pond bends away from the air-water interface. Due to which the
bottom of the pond seems to be above the actual position for the observer. So,
a clear pond seems shallower than its real depth.
8.
A pencil partially
dipped in water appears bent, why?
The rays of light coming from the lower
end (part inside water) of the pencil bend away from the normal as light passes
from water (a denser medium) to air (a rarer medium). As a result a virtual
image of the part of pencil below the water is formed above the actual position
of the pencil. For the observer the part
of the pencil above and below water appear at different position and hence a
pencil partially dipped in water appears bend.
9.
Why does a ray of light
bend when it passes from one optical medium to another medium?
A ray of light bends when it passes from
one optical medium to another medium because of the change in velocity of
light. When light passes in rarer medium its velocity is comparatively more but
when the same light passes into denser medium its velocity decreases as a
result it bends.
10.
Why does a white visible
ray split into corresponding colours when it passes through a prism?
White light is actually made up of many
different colors of light, each with its own wavelength. When white light
passes through a prism, the different colors bend at different angles due to
the refraction of light. This causes the colors to spread out and form a
spectrum, with red on one end and violet on the other. This is known as
dispersion.
11.
Rainbow cannot be seen
at the midday even in the rain, why?
Rainbows are caused by the refraction,
or bending, of light as it passes through water droplets, such as rain. For a
rainbow to be visible, the sun must be behind the observer and the water
droplets must be in front of the observer. Because the sun is high in the sky
during mid-day, the light is coming from above and the water droplets are
below. This means that the light is passing through the water droplets at a
mostly at 900 or normal with the rain droplets making it difficult
for the light to be refracted enough to form a rainbow.
12.
Light does not disperse
through a glass slab, why?
When light passes through glass, it
encounters two interfaces-one entering and the other leaving. It slows down at
the first interface and speeds back up at the second. If the two interface
surfaces are parallel to each other, as in a 'slab' of glass, all of the
bending (and dispersion) that takes place at the first interfaces is exactly
reversed at the second, 'undoing' the effect of the first interface; so
although the emerging ray of light is displaced slightly from the entering ray,
it travels in the same direction as the incoming ray and all wavelengths that
separated at the first interface are re-combined.
13.
Stars twinkle but
planets do not, why?
The rays of light coming from the star
suffer atmospheric refraction due to the varying optical densities of air at
different altitudes. The continuously change in atmospheric density refract the
light from the stars in varying amount and different directions from one moment
to next. When atmosphere refract more starlight towards us, the star appears to
be bright and when the atmosphere refracts less, the starlight appears dimmer.
In this way stars appears twinkling.
On the other hand, planets are quite
close to the earth. So, the intensity of light that we receive from the planets
is very high. As a result, despite of being varying atmospheric layer, the
light from the planets reach to our eyes with negligible refraction. Hence, they
are not seems twinkling.
14.
The sun near the horizon
appears flattened at the sunset and sunrise, why?
When the rays of light of the sun enters
the earth’s atmosphere, they get refracted at the varying angle at different
layer of atmosphere. This causes the apparent flattening of the sun.
15.
The sun is visible two
minutes before the actual sunrise, why?
The Earth's atmosphere consists of
layers of air with varying densities, and each layer has a different refractive
index. When sunlight enters the Earth's atmosphere, it encounters these
different layers and undergoes refraction, causing the light to bend.
Atmospheric refraction causes the
apparent position of the sun to be slightly higher in the sky than its actual
position. As a result, even when the center of the sun is still below the
horizon, the top edge of the sun becomes visible. This is why we see the sun
two minutes before the actual sunrise,
16.
The sun set occurs about
two minutes after the sunset, why?
During the sunset, the light rays from
the sun is actually below the horizon. They get refracted towards the earth.
While traveling from rarer to the denser medium of the atmosphere, the sunlight
reaches the observer from the apparent position of the sun. This enables us to
see the apparent sunset for a while even after the actual sunset.
17.
Why does air bubbles
inside water shine?
It is well known to us that water is
optically denser medium and air is rare medium. When light rays passes into the
air present inside the water bubble at the angle greater than the critical
angle of water, they undergo total internal reflection. The reflected rays enter
the observer’s eye. Due to this reason the bubble inside water shines.
18.
Sound is not heard at a
long distance during the day, why?
During the day time, the land get heated
faster and it makes the air above it warm. The warm air rises and the air above
the land act as rarer medium while the upper layer is comparatively cooler and
act as denser medium. When sound travel from the ground, most of its wave
travel upward due to the bending of sound from rarer to denser medium. As a
result the sound become fader at the bottom layer and cannot be heard at a
longer distance during the day.
19.
Sound is heart at a long
distance during the night. Give reason.
During night, the land get cooler faster
and the air above it act as rarer medium. When sound travels from the ground at
night it undergo total internal reflection. As a result, most of the sound wave
undergo total internal reflection and hence sound is heard at the longer distance
during night.
20.
A person hits a spear to
a fish at the place where it is seen in water, but the fish escapes. Why?
A person hits a spear to a fish at the
place where it is seen in water, but the fish escapes because of the refraction
of light. The rays of light coming from the fish inside water when passes from
water to air bends away from the normal. As a result an apparent image of the
fish is formed at the higher level and ahead from the actual position of the
fish. For the observer, the apparent image seen as a real fish and hence
instead of hitting the real fish he hits the apparent image.
21.
When we enter a cinema
hall after the film is started, we do not see the audience on their seat
clearly. Why?
When we are outside the cinema hall, the
pupil of the eye is small in the bright light. When we enter a cinema hall
after the film is started, the iris muscles could not contract immediately to
enlarge the size of pupil. As a result small amount of light enter into the eye
and hence we do not see the audience on their seat clearly but after sometime
the pupil enlarges and sufficient amount of light enter into the eye and we see
the audience.
22.
We feel difficult to
open our eyes in very bright light. Give reason.
We feel difficult to open our eyes in
very bright light because of the way our eyes work. The iris, the colored part
of the eye, controls how much light enters the eye. When we are in a dark room,
the iris opens wide to let in more light. When we are in a bright room, the
iris closes to let in less light.
However, it takes time for the iris to
adjust to changes in light. When we go from a dark room to a bright room, the
iris can't close fast enough to prevent too much light from entering the eye.
This can cause pain, discomfort, and even temporary blindness.
23. Why does light ray not deviate when it passes through normal in
any optical medium? Give reason.
When light rays passes through normal from one optical medium to
another, the angle of incidence is zero with the normal. Therefore, the angle
of refraction also becomes zero
24. What are the causes of cataract?
The causes of cataract are:
a) When a person grow old or aging.
b) Eye injury
c) Diabetes
d) Heridity factor
25.
What are the functions
of rod and con cells?
Rod cells are photoreceptor cells in the
retina of the eye that are responsible for vision in low light conditions. They
are are very sensitive to motion.
Cone cells are photoreceptor cells in
the retina of the eye that are responsible for vision in bright light
conditions and for color vision.
26.
Write down the uses of
convex lens.
Three uses of convex lens are:
i)
It is used to make microscope, telescope.
ii)
It is used for the remedy of long sightedness.
iii)
It is used in camera.
27. What type of defect of vision is shown in the given figure? Draw a
diagram showing the correction of the defect.
The defect of vision shown in the diagram is short sightedness. The
diagram showing the correction of the defect is:
Which defect of vision is shown in the given diagram? Redraw the diagram showing the remedy of such defect.
The defect of vision shown in the diagram is long-sightedness. The remedy
of the defect is shown in the diagram below
Write down the uses of
concave lens.
The uses of concave lens are:
a)
It is used in the correction of myopia.
b)
It is used in projectors and cameras to
diverge the light to larger area.
c)
It is used in spotlight and stage to
spread the light to larger area.
d)
It is used in optical instrument like
microscope and telescope to magnify the light.
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