Answer: The human eye is compared with a camera because its lens system forms an image of an object on a light-sensitive screen called the retina. The eye lens focuses light on the retina, similar to how a camera lens forms an image on its screen.

Answer: The cornea is a transparent membrane forming the front surface of the eyeball. Most of the refraction of light entering the eye occurs at the outer surface of the cornea.

Answer: The iris is a dark muscular diaphragm that controls the size of the pupil. The pupil regulates the amount of light entering the eye.

Answer: The retina is a delicate, light-sensitive membrane containing a large number of light-sensitive cells. These cells are activated by light and generate electrical signals which are sent to the brain through the optic nerve.

Answer: The eye lens forms an inverted real image of the object on the retina.

Answer:

The human eye is a sensitive sense organ that enables us to see objects and colours around us. It works somewhat like a camera. The main steps involved in the working of the human eye are:

1. Entry of light: Light from an object enters the eye through the transparent cornea.
2. Control of light: The iris controls the size of the pupil. The pupil regulates the amount of light entering the eye.
3. Refraction and focusing: Most of the refraction of light entering the eye occurs at the outer surface of the cornea. The crystalline eye lens provides the finer adjustment of focal length needed to focus objects at different distances.
4. Formation of image: The eye lens forms an inverted real image of the object on the light-sensitive retina.
5. Conversion into electrical signals: The light-sensitive cells present in the retina are activated when light falls on them and generate electrical signals.
6. Transmission to the brain: These electrical signals are carried to the brain through the optic nerve.
7. Perception: The brain processes and interprets these signals, enabling us to perceive the object.

Conclusion: Thus, the human eye receives light, focuses it on the retina, converts the light information into electrical signals and sends these signals to the brain, which enables us to see objects.

Answer: The ability of the eye lens to adjust its focal length so that objects at different distances can be focused clearly on the retina is called the power of accommodation.

Answer: When viewing a distant object, the ciliary muscles relax. The eye lens becomes thinner, its focal length increases and the distant object is focused clearly on the retina.

Answer: For a nearby object, the ciliary muscles contract. This increases the curvature of the eye lens, making it thicker. Its focal length decreases and the nearby object is focused clearly on the retina.

Answer: The minimum distance at which an object can be seen clearly without strain is called the least distance of distinct vision or near point of the eye.

For a young adult with normal vision, it is approximately 25 cm.

Answer: The farthest point up to which a normal eye can see objects clearly is called the far point. For a normal eye, the far point is infinity.

Answer: The focal length of the eye lens cannot be decreased beyond a certain minimum limit. Therefore, an object placed closer than about 25 cm cannot be focused clearly on the retina without strain.

Answer: Cataract is a condition in which the crystalline lens of the eye becomes cloudy or milky. It can cause partial or complete loss of vision and can be treated through cataract surgery.

Answer:

1. Myopia or near-sightedness
2. Hypermetropia or far-sightedness
3. Presbyopia

Answer: Myopia is also called near-sightedness. A person with myopia can see nearby objects clearly but cannot see distant objects distinctly.

In a myopic eye, the image of a distant object is formed in front of the retina.

Myopia is corrected using a concave lens of suitable power.

Answer: Myopia may arise due to:

1. Excessive curvature of the eye lens.
2. Elongation of the eyeball.

Answer: Hypermetropia is also called far-sightedness. A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.

It is corrected using a convex lens of appropriate power.

Answer: Hypermetropia may arise because:

1. The focal length of the eye lens is too long.
2. The eyeball has become too small.

Answer: Presbyopia is a defect of vision in which the power of accommodation of the eye decreases with ageing. The near point gradually recedes and the person finds it difficult to see nearby objects clearly.

Answer: Some people may suffer from both myopia and hypermetropia. Such people may require bifocal lenses.

The upper portion generally consists of a concave lens for distant vision, while the lower portion consists of a convex lens for near vision.

Solution: Given:
P = –5.5 D

Therefore: Answer: f ≈ –18.2 cm
The negative sign indicates a concave lens.

Solution: Answer: f ≈ +66.7 cm
The positive sign indicates a convex lens.

Solution: For a distant object: Using the lens formula: Therefore: Power: Answer: A concave lens of power –1.25 D is required.

Solution: Using: Therefore: Hence: Answer: A convex lens of power +3 D is required.

Answer: A triangular glass prism is a transparent optical element having two triangular bases and three rectangular lateral surfaces. The two lateral surfaces are inclined to each other.

Answer: The angle between the two lateral refracting surfaces of a prism is called the angle of the prism.

Answer: The angle through which the emergent ray deviates from the direction of the incident ray is called the angle of deviation.

Answer: When light enters glass from air, it bends towards the normal.

When it travels from glass to air at the second surface, it bends away from the normal.

Answer: The splitting of white light into its component colours is called dispersion of light.

Answer: The seven colours are: The sequence is remembered using the acronym VIBGYOR.

Answer: Violet light deviates the most.

Answer: Red light deviates the least.

Answer: Different colours of light bend through different angles when passing through a prism. Red light bends the least while violet light bends the most. Therefore, the colours emerge along different paths and form a spectrum.

Answer: The band of coloured components obtained from a beam of light is called its spectrum.

Answer: A rainbow is a natural spectrum appearing in the sky after a rain shower. It is produced by the dispersion of sunlight by tiny water droplets in the atmosphere.

Answer: Water droplets in the atmosphere act like small prisms. Sunlight entering a water droplet undergoes refraction and dispersion, followed by internal reflection, and then refraction again when the light emerges from the droplet.

The different colours then reach the observer's eye and form a rainbow.

Answer: A rainbow is generally formed in the direction opposite to the Sun.

Answer: The refraction of light caused by the Earth's atmosphere is called atmospheric refraction.

Answer: The twinkling of stars is due to atmospheric refraction of starlight.

Starlight passes through layers of the atmosphere having continuously changing refractive index. The apparent position and brightness of the star keep changing slightly, causing the twinkling effect.

Answer: Planets are much closer to Earth and appear as extended sources rather than point sources. The variations in light coming from different parts of the planet tend to average out, so the twinkling effect is not noticeable.

Answer: The Sun is visible about two minutes before actual sunrise because of atmospheric refraction. The apparent position of the Sun is higher than its actual position due to refraction by the atmosphere.

Answer: Atmospheric refraction causes the apparent position of the Sun to be above the horizon even after the Sun has actually crossed the horizon. Therefore, the Sun remains visible for about two minutes after actual sunset.

Answer: Scattering of light is the phenomenon in which light interacts with fine particles present in a medium and gets scattered in different directions.

Answer: The scattering of light by colloidal particles is called the Tyndall effect. It makes the path of a beam of light visible.

Answer: The path of sunlight becomes visible when a fine beam enters a smoke-filled room through a small opening.

Answer: Fine particles and molecules in the atmosphere scatter shorter wavelengths of light more strongly than longer wavelengths. Blue light is scattered more strongly than red light, and the scattered blue light enters our eyes.

Hence, the clear sky appears blue.

Answer: Red light is scattered the least by fog or smoke. Therefore, red light can be seen from a greater distance and is used for danger signals.

Answer: At very high altitudes, scattering of sunlight is not prominent because there is much less atmosphere. Therefore, the sky appears dark instead of blue.