Class 10 Science, Chapter 10 (NCERT). 15 questions by concept. Open “Show answer” for the answer and why.
How to teach this chapter · Common misconceptions & worked visual for this chapter
Which part of the eye controls the size of the pupil to adjust how much light enters?
(b) Iris
The iris is a muscular diaphragm that controls the size of the pupil, regulating how much light enters the eye. The cornea and lens refract light, and the retina detects the focused image.
What kind of image does the eye lens form on the retina?
(a) Real and inverted
The eye lens forms a real and inverted image on the retina. The visual system then interprets this signal so the scene is perceived upright.
For a young adult with normal vision, what are the near point and the far point of the eye?
(d) 25 cm and infinity
A normal young eye has a near point near 25 cm and a far point effectively at infinity.
A distant object is viewed. What does the eye change in order to focus objects at different distances?
(c) The focal length of the lens
Ciliary muscles change the curvature of the lens. This changes the focal length of the lens. The retina stays fixed in place. For a distant object the lens becomes thinner and its focal length increases.
A person's near point is 1 m instead of 25 cm. Which defect of vision is this?
(b) Hypermetropia
A distant near point means near objects are blurred while distant ones are clear. This is hypermetropia, or far-sightedness.
In a hypermetropic eye, why is a near object seen blurred?
(c) Its image forms behind the retina
In hypermetropia, light from a near object focuses behind the retina, so the image on the retina is blurred.
Which pattern of vision is typical of hypermetropia without spectacles?
(c) Nearby objects blurred; distant objects clear
In hypermetropia, nearby objects appear blurred while distant objects are seen clearly. The image of a nearby object would form behind the retina.
In a myopic eye, why is a distant object seen blurred?
(d) Its image forms in front of the retina
In myopia, light from a distant object focuses in front of the retina, so the image on the retina is blurred.
Which lens corrects myopia and hypermetropia occurring together in the same eye?
(b) Bifocal lens
A bifocal lens has two parts of different power: a concave upper part for distant vision and a convex lower part for near vision.
Why does vision remain poor in severe cataract despite wearing spectacles?
(d) Clouding of the eye lens
Severe cataract clouds the eye lens and obstructs clear vision. Changing spectacle power cannot remove this clouding. Weak ciliary muscles and eyeball elongation cause different vision problems.
Why does a glass prism split white light into a band of colours?
(c) Different colours have different refractive indices in glass
White light has many colours, and each colour has a different refractive index in glass. So each colour bends by a different amount, and the prism spreads them into a band from red to violet.
How does the emergent ray from a triangular prism differ from the emergent ray from a rectangular glass slab?
(a) It is deviated from the incident direction
A slab has parallel faces, so the ray emerges parallel to its original direction, only shifted sideways. A prism's faces are not parallel. Its ray emerges at an angle to the incident ray.
Why do planets not twinkle the way stars do?
(c) They are extended sources
A planet is much nearer and looks like a small disc, an extended source. The changes in light from its many points average out, so it does not twinkle.
Near the horizon, where does the Sun appear to be compared with its actual geometric position?
(d) Above it
Atmospheric refraction bends light from the Sun as it passes through layers of air near the horizon. This makes the apparent position of the Sun lie above its actual geometric position. That is why apparent sunrise happens before actual sunrise, and apparent sunset happens after actual sunset.
Why does the sky look dark to an astronaut in space but blue from the ground?
(d) There is no atmosphere to scatter sunlight
The blue colour of the sky is caused by scattering of sunlight by air molecules. In space there is no atmosphere, so there is nothing to scatter sunlight and the sky appears dark to an astronaut.
Wrong
Near-sightedness needs a converging lens to make distant objects clear.
Why it feels right. Stronger convergence sounds like better focus.
Right
A diverging lens helps move the focus of distant light back onto the retina.
Worked example
