Light Test

Result

Light Test - 10

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Question 1
1 / -0

A medium through which light passes fully is called

A
transparent

B
opaque

C
translucent

D
alloy

Solution

A medium through which light passes fully is called transparent.
Question 2
1 / -0

Which of the following electromagnetic waves has the longest wavelength?

A
Heat waves

B
Visible light

C
Micro Waves

D
Radio frequency waves

Solution

In the image we can see that radio waves have longest wavelength and lowest frequency.
Question 3
1 / -0

The formation of umbra and penumbra regions of the shadow of an opaque sphere by a small light source is due to

A
wave nature of light

B
rectilinear propagation of light

C
capacity of light to bend around the obstacle

D
unequal reflections of light from different parts of the obstacle

Solution

When light from a source falls on an opaque sphere, the shadow is formed by the sphere opposite to the source side. This shadow can divided into two regions called umbra and penumbra. The region where all of the light from the source is blocked by the object is called umbra and the region where the shadow is only partial is called penumbra. This phenomenon occurs due to rectilinear propagation of light.
Question 4
1 / -0

An illuminating object is placed between two plane mirrors mutually perpendicular to each other. The number of images formed is

A
4

B
3

C
2

D
6

Solution

An illuminating object is placed between two plane mirrors mutually perpendicular to each other. The number of images formed is 3.
n = 360/90 - 1 = 4 - 1 = 3
Question 5
1 / -0

When a plane mirror is placed horizontally on ground level at a distance of 60 m from the foot of a tower, the top of the tower and its image in the mirror subtends an angle of 90^o at the eye. The height of the tower is

A
30 m

B
60 m

C
90 m

D
120 m

Solution
Question 6
1 / -0

When an object is placed beyond the centre of curvature for the concave mirror, the characteristics of the image will be

A
real and inverted image

B
virtual, inverted and magnified image

C
virtual, erect and diminished image

D
No image is formed

Solution

When an object is placed beyond the centre of curvature for the concave mirror, the characteristics of the image will be real and inverted.
Question 7
1 / -0

A dentist uses a small mirror that gives a magnification of 4 when it is held 0.60 cm from a tooth. The radius of curvature of the mirror is

A
1.60 cm (convex)

B
0.8 cm (concave)

C
1.60 cm (concave)

D
0.8 cm (convex)

Solution

m = -v/u
4 = -v/(-0.6)
v = 2.4 cm
1/f = 1/v + 1/u
1/f = 1/2.4 - 1/0.6
1/f = -3/2.4
f = - 0.8 cm
R = - 1.6 cm
Mirror is concave.
Question 8
1 / -0

A coin dropped in water of refractive index 4/3 up to a real depth of 28 cm will apparently seem to be at a depth of

A
21 cm

B
7 cm

C
14 cm

D
5 cm

Solution

Real depth/Apparent depth
4/3 = 28/Apparent depth
Apparent Depth = 21 cm
Question 9
1 / -0

The refractive index of water is (4/3) and that of glass is (3/2). If the speed of light in glass is 2 10⁸ m/s, the speed of light in water will be

A
1 10⁸ m/s

B
(9/4) 10⁸ m/s

C
(8/3) 10⁸ m/s

D
4 10⁸ m/s

Solution

Refractive index for glass = 3/2

= c/v_g x v_w/c
3/2 x 3/4 = v_w/2 x 10⁸v_w= 9/4 x 10⁸ m/s
Question 10
1 / -0

Where should an object be placed so that a real and inverted image of the same size is obtained using a convex lens?

A
Between the lens and its focus

B
At the focus

C
At twice the focal length

D
At infinity

Solution

At twice the focal length a real and inverted image of the same size is obtained using a convex lens.
Question 11
1 / -0

The minimum distance between an object and its real image formed by a convex lens is

A
2f

B
4f

C
f

D
zero

Solution
Question 12
1 / -0

In order to increase the magnifying power of a telescope,

A
the focal powers of the objective and the eye piece should be large

B
the objective should have small focal length, and the eye piece should be large

C
both should have large focal lengths

D
the objective should have large focal length and the eye- piece should have small

Solution

In order to increase the magnifying power of a telescope, the objective should have large focal length and the eye-piece should have small.
Question 13
1 / -0

In a compound microscope, the intermediate image is

A
virtual, erect and magnified

B
real, erect and magnified

C
real, inverted and magnified

D
virtual, erect and reduced

Solution

In a compound microscope, the intermediate image is real, inverted and magnified.
Question 14
1 / -0

In dispersion by a prism, we can see the colours in the decreasing order of deviation as :

A
blue, violet, yellow, red

B
red, yellow, violet, indigo

C
red, yellow, green, orange

D
orange, yellow, green, blue

Solution

In dispersion by a prism, we can see the colours in the order: orange, yellow, green, blue.
Question 15
1 / -0

'Dispersion' is the term used to describe

A
propagation of light in straight lines

B
splitting of a beam of light into component colours

C
bending of a beam of light when it strikes a mirror

D
change that takes place in white light after passage through red glass

Solution

'Dispersion' is the term used to describe splitting of a beam of light into component colours.
Question 16
1 / -0

To astronauts in a space ship, the sky appears dark because

A
light from the sky is absorbed by the medium

B
the fact that human eye becomes blind to the blue colour

C
there is no atmosphere

D
of cosmic rays

Solution

To astronauts in a space ship, the sky appears dark because there is no atmosphere.
Question 17
1 / -0

Mirages are observed in deserts due to the phenomenon of

A
double reflection of light

B
total internal reflection

C
refraction

D
scattering of light

Solution

Mirages are observed in deserts due to the phenomenon of total internal reflection of light.
Question 18
1 / -0

In cold countries, the phenomenon of looming (i.e. ship appears in the sky) takes place, because refractive index of air

A
decreases with height

B
increases with height

C
does not change with height

D
becomes infinity at the surface

Solution

In cold countries, the phenomenon of looming (i.e. ship appears in the sky) takes place, because refractive index of air decreases with height.
Question 19
1 / -0

The power of the eye lens to adjust its focal length according to the distance so that image is formed on the retina, is called

A
astigmatism

B
accommodation

C
magnification

D
none of the above

Solution

The power of the eye lens to adjust its focal length according to the distance so that image is formed on the retina, is called accommodation.
Question 20
1 / -0

A person can see clearly up to 3 metres. If he wants to see up to 12 metres, he should use a

A
convex lens

B
concave lens

C
concavo–convex lens

D
cylindrical lens.

Solution

A person can see clearly up to 3 metres. If he wants to see up to 12 metres, he should use a concave lens.