Extra 30 short questions and answers from the chapter:10 "Human Eye and Colourful World" for Class 10 CBSE Science:
What is the least distance of distinct vision?
The least distance of distinct vision for a normal human eye is
25 cm
. This means that an object must be at least
25 cm
away from the eye for clear vision.
Define power of accommodation of the eye.
The
power of accommodation
is the ability of the eye to focus on both near and distant objects by adjusting the focal length of the
eye lens
using
ciliary muscles
.
What is myopia? What causes it? How is it corrected?
Myopia (short-sightedness)
is a defect where a person can see
nearby
objects clearly but
distant
objects appear blurred.
It is caused due to:
Elongation of the eyeball
Excessive curvature of the eye lens
It is corrected using a
concave lens
, which diverges the light rays before they enter the eye.
What is hypermetropia? How is it corrected?
Hypermetropia (far-sightedness)
is a defect where a person can see
distant
objects clearly but
nearby
objects appear blurred.
It is caused due to:
Shortening of the eyeball
Less curvature of the eye lens
It is corrected using a
convex lens
, which converges the light rays before they enter the eye.
What is presbyopia? How is it corrected?
Presbyopia
is an age-related defect where both
near
and
distant
objects become difficult to see due to weakening of
ciliary muscles
and
reduced flexibility of the eye lens
.
It is corrected using
bifocal lenses
, which have
concave lenses for distant vision
and
convex lenses for near vision
.
What is astigmatism? How is it corrected?
Astigmatism
is a vision defect where objects appear distorted due to
uneven curvature of the cornea or eye lens
.
It is corrected using
cylindrical lenses
.
What is the role of the retina in human vision?
The
retina
is the light-sensitive screen of the eye where an image is formed. It contains
rods and cones
that detect light and colour, converting them into electrical signals sent to the
optic nerve
.
What is the role of the iris in the human eye?
The
iris
controls the amount of light entering the eye by adjusting the size of the
pupil
. It expands in
dim light
to allow more light in and contracts in
bright light
to reduce light entry.
Explain why the image formed on the retina is inverted, but we see objects upright.
The lens forms a
real and inverted
image on the
retina
. The
brain processes this image
and automatically corrects it to appear upright.
Why do older people need reading glasses?
With age, the
ciliary muscles weaken
, and the
lens loses flexibility
, making it difficult to focus on nearby objects. This condition is called
presbyopia
and is corrected with
convex lenses
in reading glasses.
What is atmospheric refraction? Give an example.
Atmospheric refraction
is the bending of light when it passes through layers of the atmosphere with different densities.
Example:
Twinkling of stars
and
apparent early sunrise and delayed sunset
.
Why do stars twinkle?
Due to
atmospheric refraction
, the light from stars
bends
when passing through different layers of the atmosphere. This causes stars to appear
brighter or dimmer
, making them twinkle.
Why does the sun appear red during sunrise and sunset?
During sunrise and sunset, sunlight travels through a
larger
portion of the atmosphere, scattering
blue and violet light
away, leaving only
red light
, which reaches our eyes.
Why do planets not twinkle like stars?
Planets appear as
large
sources of light due to their proximity to Earth. The effects of
atmospheric refraction
average out, preventing twinkling.
Why does the sky appear blue?
The
scattering of light
by air molecules causes shorter wavelengths (blue) to scatter more than longer wavelengths (red), making the sky appear
blue
.
What is the Tyndall effect? Give an example.
The
Tyndall effect
is the scattering of light by small particles in a medium.
Example:
Sunlight passing through mist or dust
.
Why are danger signals and traffic lights red?
Red light
is scattered the least in the atmosphere and can be seen from a greater distance, making it ideal for warning signs and signals.
What is dispersion of light?
Dispersion
is the splitting of white light into its
seven constituent colours
(VIBGYOR) when passing through a
prism
.
What is a spectrum?
A
spectrum
is a band of
seven colours
(Violet, Indigo, Blue, Green, Yellow, Orange, Red) obtained when white light is dispersed.
How is a rainbow formed?
A rainbow is formed due to
refraction, dispersion, and internal reflection
of sunlight inside raindrops. The dispersed light emerges as a colourful arc.
Why do clouds appear white?
Clouds contain large water droplets that scatter all wavelengths of light
equally
, making them appear
white
.
Why is the sun white at noon?
At noon, the sun is
overhead
, and light travels through a
shorter
distance in the atmosphere, experiencing
less scattering
, making the sun appear
white
.
Why does the bottom of a pond appear shallower than it is?
Due to
refraction
, light bends away from the normal when moving from
denser
(water) to
rarer
(air) medium, making the pond bottom appear
closer
than its actual depth.
Why do we use convex lenses in magnifying glasses?
Convex lenses
converge light rays and create a
larger, magnified image
of an object when placed within the focal length.
What is the principle behind optical
fibres
?
Optical
fibres
work on the principle of
total internal reflection
, where light is
trapped and guided
through the
fibre
without escaping.
Why do we use concave mirrors in torches and car headlights?
Concave mirrors reflect light to form a
parallel beam
, ensuring a focused and bright light output.
What happens to the focal length of the eye lens when focusing on nearby objects?
The
focal length decreases
because the
ciliary muscles contract
, making the lens
thicker
.
What is meant by persistence of vision?
It is the ability of the eye to retain an image for
1/16th of a second
after the object is removed. It is used in
movies and animation
.
What is the role of a prism in a spectrometer?
A
prism
disperses light into its spectrum, allowing spectrometers to study
light composition
.
How does the human eye differ from a camera?
Unlike a camera, the human eye adjusts its
focal length naturally
(accommodation), has
automatic brightness control
, and can detect
a wide range of colours
.
