Draw ray diagrams each showing (i) myopic eye and (ii) hypermetropic eye.
Ray diagrams show:
(i) Myopic eye: Light rays from a distant object focus in front of the retina.
(ii) Hypermetropic eye: Light rays from a nearby object focus behind the retina.
A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give her? Draw ray diagram for the correction of this defect.
The student is suffering from myopia (near-sightedness). A doctor advises her to use a concave lens of appropriate power to correct the defect.
A concave lens diverges the incoming rays so that they focus on the retina.
How are we able to see nearby and also the distant objects clearly?
The human eye is able to see objects at different distances clearly by changing the focal length of the eye lens using its power of accommodation.
A person needs a lens of power −4.5 D for correction of her vision. (a) What kind of defect in vision is she suffering from? (b) What is the focal length of the corrective lens? (c) What is the nature of the corrective lens?
(a) The person is suffering from myopia.
(b) The focal length \( f = \dfrac{1}{P} = \dfrac{1}{-4.5} = -0.22 \text{ m} \).
(c) The corrective lens is a concave lens.
How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.
Two identical prisms are arranged such that one is placed inverted with respect to the other. The first prism disperses white light into its spectrum, and the second prism recombines the spectrum to form white light again.
Draw a ray diagram showing the dispersion through a prism when a narrow beam of white light is incident on one of its refracting surfaces. Also indicate the order of the colours of the spectrum obtained.
When white light is incident on a prism, the emergent beam splits into a spectrum of seven colours. The order from top to bottom is: Violet, Indigo, Blue, Green, Yellow, Orange, Red.
Is the position of a star as seen by us its true position? Justify your answer.
No. Due to atmospheric refraction, the light from stars bends as it enters layers of air with varying refractive indices. Hence, the star appears slightly higher than its actual position.
Why do we see a rainbow in the sky only after rainfall?
After rainfall, a large number of water droplets remain suspended in the atmosphere. These droplets act like small prisms and disperse sunlight, producing a rainbow.
Why is the colour of the clear sky blue?
The blue colour of the sky is due to the scattering of light. Blue light is scattered the most by atmospheric particles because it has a shorter wavelength.
What is the difference in colours of the Sun observed during sunrise/sunset and at noon? Give explanation for each.
During sunrise and sunset, the Sun appears reddish because sunlight travels a longer atmospheric path and blue light is scattered away. At noon, the Sun appears white because it travels a shorter path and scattering is minimal.