A student traces the path of a ray of light through a glass prism as shown in the diagram, but leaves it incomplete and unlabelled. Redraw and complete the diagram. Also, label on it ∠ i , ∠ e , ∠ r and ∠ D .

The required diagram is given below: A triangular glass prism is a transparent object made up of glass having two triangular bases and three rectangular lateral surfaces. Here, TP - Incident ray, PO - Refracted ray, OR - Emergent ray, ∠ A - Angle of the prism, ∠ i - AngIe of incidence, ∠ r - Angle of refraction, ∠ e - Angle of emergence and ∠ D - Angle of deviation. The angle between the incident ray and normal is called the angle of incidence, represented as i . The angle between refracted ray and normal is called the angle of refraction, represented as r . The angle of the light coming out of a medium is called the angle of emergence. In refraction through a glass prism, the emergent ray is deviated from its original direction by a certain angle. The angle between the incident ray and emergent ray is called the angle of deviation.

Differentiate between a glass slab and a glass prism.

Glass slab Glass prism It has 3 parallel pairs of refracting surfaces It has 3 rectangular refracting surfaces inclined to each other bounded with 2 parallel triangular surfaces Incident ray and emergent ray are parallel to each other Incident ray and emergent ray are not parallel to each other

When do we consider a person to be myopic or hypermetropic? List two causes of hypermetropia. Explain using ray diagrams how the defect associated with hypermetropic eye can be corrected.

The defect of the human eye in which a person can see the objects lying at short distances clearly but cannot see the far objects distinctly is called myopia. The defect of the human eye in which a person can see the objects lying at long distances clearly, but cannot see the nearby objects distinctly is called hypermetropia. The following are the causes of hypermetropia (i) Increase in the focal length of the eye lens (ii) The size of the eyeball becomes too short In a normal eye, the rays from the near point are focussed on the retina is 25 cm . In a hypermetropic eye, the rays from the normal near point are focussed at a point beyond the retina of the eye. So the objects lying at the near point are not seen clearly. To correct a hypermetropic eye, the person is allowed to wear spectacles with a convex lens of suitable power. When a convex lens or converging lens of suitable power is placed in front of the hypermetropic eye, then the diverging rays of light coming from the nearby object are first converged by this convex lens. Thus, the convex lens forms a virtual image of the nearby object (lying at O ' ) at the point O of the hypermetropic eye which can be easily focused by the eye lens to form an image on the retina.

Draw a labelled diagram to show (i) reddish appearance of the sun at the sunrise or the sunset and (ii) white appearance of the sun at noon when it is overhead.

Scattering of light that helps us to understand the bluish colour of the sky and the reddish appearance of the Sun at the sunrise or the sunset. (i) Near the horizon, most of the blue light and shorter wavelengths are scattered away by the particles. Therefore, the light that reaches our eyes is of longer wavelengths. This gives rise to the reddish appearance of the Sun. (ii) Light from the Sun overhead would travel relatively shorter distance. At noon, the Sun appears white as only a little of the blue and violet colours are scattered.

Why is Tyndall effect shown by colloidal particles? State four instances of observing the Tyndall effect.

The phenomenon of scattering of light by the colloidal particles gives rise to Tyndall effect. Some examples of Tyndall effects are: Tyndall effect is seen when a fine beam of sunlight enters a smoke-filled room through a small hole. Thus, scattering of light makes the particles visible. Tyndall effect can also be observed when sunlight passes through a canopy of a dense forest. Here, tiny water droplets in the mist scatter light. Sky appears blue due to scattering of shorter wavelengths. Sunrise or sunset appears as red due to scattering of longer wavelengths.

Why does the sun appear reddish early in the morning ? Will this phenomenon be observed by an astronaut on the Moon ? Give reason to justify your answer.

During the sunrise the sun is set close to the Earth’s horizon, and therefore light travels a longer distance through the Earth. Particles suspended in the air distribute the light in shorter wavelengths such as blue. The light that passes through the Earth has a long wavelength that is red. As a result, the sun appears practically reddish because only the least scattered red colour ( λ b < λ r ) is received by our sight and appears to emanate from the sun. This is why the sun seems reddish in the early morning. Because the moon has no atmosphere, the astronaut will not be able to see this occurrence on the surface.

Write the function of ciliary muscles of human eye.

The ciliary muscle is an intrinsic eye muscle that forms a ring of smooth muscle in the central layer of the eye (vascular layer). It regulates the flow of aqueous humour into Schlemm's canal and governs accommodation for viewing objects at different distances. The zonules are relaxed or tightened by this muscle, allowing the lens to change shape for focusing. The zonules are fibres that keep the lens in place while allowing it to change shape during accommodation.

Write the function of crystalline lens of human eye.

The crystalline lens, also known as the lens of the eye, is an important part of the anatomy of the eye that allows the eye to focus on objects at different distances. It is situated in front of the vitreous body, behind the iris. It's also bendable, allowing it to change shape and bend light to appropriately focus on the retina.