Human Eye and Colourful World Test

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Human Eye and Colourful World Test - 57

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Weekly Quiz Competition

Question 1
1 / -0

A person is suffering from myopic defect. He is able to see clear objects placed at $15\ cm$ . What type and of what focal length of lens he should use to see clearly the objects placed $60\ cm$ away

A
Concave lens of $20\ cm$ focal length

B
Convex lens of $20\ cm$ focal length

C
Concave lens of $12\ cm$ focal length

D
Convex lens of $12\ cm$ focal length

Solution

Lens should be used such that the image of an object placed at $60 \ cm$ is formed at $15 \ cm$

Hence, in the given case $u=-60 \ cm$ ; $v=-15 \ cm$
Using the lens' formula $\dfrac 1f=\dfrac{1}{v}-\dfrac{1}{u}$

$\Rightarrow \dfrac 1f=\dfrac{1}{-15}-\dfrac{1}{-60} = \dfrac{-3}{60}$

$\Rightarrow f=-20\ cm$ .

Hence, the person should use concave lens of focal length $20 \ cm$
Question 2
1 / -0

The hyper-metropia is a

A
Short-side defect

B
Long-side defect

C
Bad vision due to old age

D
None of these

Solution

The hyper-metropia is an eye defect when person faces difficulty in seeing nearby objects(Short Sight) but not far-sided objects (Long Sight). Due to inability of the eye lens to converge light rays from nearby objects at the retina, image is formed behind the retina. Long sight leads to problems with near vision. So hyper-metropia is a Long-side defect.
Question 3
1 / -0

At sun rise of sunset, the sun looks more red than at mid-day because

A
The sun is hottest at these times

B
Of the scattering of light

C
Of the effects of refraction

D
Of the effects of diffraction

Solution

$I\propto\dfrac{1}{{\lambda}^4}$
According to Rayleigh’s law of scattering, intensity scattered is inversely proportional to the forth power of wavelength. So red is least scattered and sun appears Red.
Question 4
1 / -0

Stars are twinkling due to

A
Diffraction

B
Reflection

C
Refraction

D
Scattering

Solution

Stars twinkle due to variation in $R.l$ of atmosphere.
Stars are twinkling due to refraction,
Question 5
1 / -0

A person is suffering from 'presbyopia' ( myopia and hyper metropia both defects ) should use

A
A concave lens

B
A convex lens

C
A bifocal lens whose lower portion is convex

D
A bifocal lens whose upper portion is convex

Solution

A bifocal lens consists of both convex lenses with lower part is convex.
Question 6
1 / -0

A person uses a lens of power $+3\ D$ to normalise vision. Near point of hypermetropic eye is

A
$1\ m$

B
$1.66\ m$

C
$2\ m$

D
$0.66\ m$

Solution

Focal length of the lens $f=\dfrac{100}{3}\ cm$
By lens formula $\dfrac 1f=\dfrac 1v-\dfrac 1u$
$\Rightarrow \dfrac{1}{+100/3}=\dfrac 1v-\dfrac {1}{-25}\Rightarrow v=-100\ cm=-1\ m$
Question 7
1 / -0

A person wears glasses of power $-2.5\ D$ . The defect of the eye and the far point of the person without the glasses are respectively

A
Farsightedness, $40\ cm$

B
Nearsightedness, $40\ cm$

C
Astigmatism, $40\ cm$

D
Nearsightedness, $250\ cm$

Solution

Negative power is given, so defect of eye is nearsightedness
Also defected far point $=-f=-\dfrac 1p=-\dfrac{100}{(-2.5)}=40\ cm$
Question 8
1 / -0

To remove myopia ( short sightedness ) a lens of power $0.66\ D$ is required. The distant point of the eye is approximately

A
$100\ cm$

B
$150\ cm$

C
$50\ cm$

D
$25\ cm$

Solution

Given,
Power of lens $P=0.66\ D$
Far point of the eye $=$ focal length of the lens $=\dfrac{100}{P}=\dfrac{100}{0.66}=151\ cm$
Hence, The distant point of the eye is approximately $151\ cm$
Question 9
1 / -0

Colour of the sky is blue due to

A
Scattering of light

B
Total internal reflection

C
Total emission

D
None of the above

Solution

The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. These are more effective in scattering light of shorter wavelengths at the blue end than light of longer wavelengths at the red end. Thus, when sunlight passes through the atmosphere, the fine particles in air scatter the blue colour (shorter wavelengths) more strongly than red. The scattered blue light enters our eyes.
Question 10
1 / -0

The band of seven colours that constitute white light is known as

A
Rainbow

B
Palette

C
Spectrum

D
None of these

Solution

A prism separates white light into a group of seven colors called a spectrum. These seven colors are always in the same order. The colors of the spectrum are red, orange, yellow, green, blue, indigo, and violet.

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Re-Attempt Weekly Quiz Competition

Human Eye and Colourful World Test - 57

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Human Eye and Colourful World Test - 57

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SHARING IS CARING

Question 1

Concave lens of 20 cm20\ cm20 cm focal length

Convex lens of 20 cm20\ cm20 cm focal length

Concave lens of 12 cm12\ cm12 cm focal length

Convex lens of 12 cm12\ cm12 cm focal length

Solution

Question 2

Short-side defect

Long-side defect

Bad vision due to old age

None of these

Solution

Question 3

The sun is hottest at these times

Of the scattering of light

Of the effects of refraction

Of the effects of diffraction

Solution

Question 4

Diffraction

Reflection

Refraction

Scattering

Solution

Question 5

A concave lens

A convex lens

A bifocal lens whose lower portion is convex

A bifocal lens whose upper portion is convex

Solution

Question 6

1 m1\ m1 m

1.66 m1.66\ m1.66 m

2 m2\ m2 m

0.66 m0.66\ m0.66 m

Solution

Question 7

Farsightedness, 40 cm40\ cm40 cm

Nearsightedness, 40 cm40\ cm40 cm

Astigmatism, 40 cm40\ cm40 cm

Nearsightedness, 250 cm250\ cm250 cm

Solution

Question 8

100 cm100\ cm100 cm

150 cm150\ cm150 cm

50 cm50\ cm50 cm

25 cm25\ cm25 cm

Solution

Question 9

Scattering of light

Total internal reflection

Total emission

None of the above

Solution

Question 10

Rainbow

Palette

Spectrum

None of these

Solution

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Concave lens of $20\ cm$ focal length

Convex lens of $20\ cm$ focal length

Concave lens of $12\ cm$ focal length

Convex lens of $12\ cm$ focal length

$1\ m$

$1.66\ m$

$2\ m$

$0.66\ m$

Farsightedness, $40\ cm$

Nearsightedness, $40\ cm$

Astigmatism, $40\ cm$

Nearsightedness, $250\ cm$

$100\ cm$

$150\ cm$

$50\ cm$

$25\ cm$