Read the following passage and answer the following questions.

Lenses in our eyes

In class 6 you learnt about pinhole camera. The human eye also works as a pinhole camera with two lenses. The pupil acts as a pinhole. Light falls on the cornea which acts as a converging lens. Then it falls on 'the lens’ which is behind the cornea. Through the lens, the light falls on the retina to form a real image. To focus on objects, animals can move the lens or change its shape. Fish move their lens backward and forward to focus the image of objects on their retina. Mammals change the shape of their lens. When we have to focus on the objects at a distance our lenses become thin. Due to this the light coming from the object bends less. When we focus on nearby objects, the lenses become thicker. As a result the light coming from the object bends more and falls on the retina. The shape of lenses is changed by muscles around it. When the lens needs to be thin, the muscles relax and when the lens needs to be thick, they contract. For this reason, when you read for a long time, your muscles are contracted continuously and your eyes feel tired.

How many lenses are there in our eyes?

Read the following passage and answer the following questions.

Lenses in our eyes

In class 6 you learnt about pinhole camera. The human eye also works as a pinhole camera with two lenses. The pupil acts as a pinhole. Light falls on the cornea which acts as a converging lens. Then it falls on 'the lens’ which is behind the cornea. Through the lens, the light falls on the retina to form a real image. To focus on objects, animals can move the lens or change its shape. Fish move their lens backward and forward to focus the image of objects on their retina. Mammals change the shape of their lens. When we have to focus on the objects at a distance our lenses become thin. Due to this the light coming from the object bends less. When we focus on nearby objects, the lenses become thicker. As a result the light coming from the object bends more and falls on the retina. The shape of lenses is changed by muscles around it. When the lens needs to be thin, the muscles relax and when the lens needs to be thick, they contract. For this reason, when you read for a long time, your muscles are contracted continuously and your eyes feel tired.

How does the lens change shape when we focus on distant objects?

Read the following passage and answer the following questions.

Lenses in our eyes

In class 6 you learnt about pinhole camera. The human eye also works as a pinhole camera with two lenses. The pupil acts as a pinhole. Light falls on the cornea which acts as a converging lens. Then it falls on 'the lens’ which is behind the cornea. Through the lens, the light falls on the retina to form a real image. To focus on objects, animals can move the lens or change its shape. Fish move their lens backward and forward to focus the image of objects on their retina. Mammals change the shape of their lens. When we have to focus on the objects at a distance our lenses become thin. Due to this the light coming from the object bends less. When we focus on nearby objects, the lenses become thicker. As a result the light coming from the object bends more and falls on the retina. The shape of lenses is changed by muscles around it. When the lens needs to be thin, the muscles relax and when the lens needs to be thick, they contract. For this reason, when you read for a long time, your muscles are contracted continuously and your eyes feel tired.

How do the fish focus on objects?

Read the following passage and answer the following questions.

Lenses in our eyes

In class 6 you learned about pinhole cameras. The human eye also works like a pinhole camera with two lenses. The pupil acts as a pinhole. Light falls on the cornea which acts as a converging lens. Then it falls on 'the lens’ which is behind the cornea. Through the lens, the light falls on the retina to form a real image. To focus on objects, animals can move the lens or change its shape. Fish move their lens backward and forward to focus the image of objects on their retina. Mammals change the shape of their lens. When we have to focus on the objects at a distance our lenses become thin. Due to this the light coming from the object bends less. When we focus on nearby objects, the lenses become thicker. As a result, the light coming from the object bends more and falls on the retina. The shape of lenses is changed by the surrounding muscles. When the lens needs to be thin, the muscles relax and when the lens needs to be thick, they contract. For this reason, when you read for a long time, your muscles are contracted continuously and your eyes feel tired.

What acts as a pinhole in our eyes?

Read the following passage and answer the following questions.

Lenses in our eyes

In class 6 you learnt about pinhole camera. The human eye also works as a pinhole camera with two lenses. The pupil acts as a pinhole. Light falls on the cornea which acts as a converging lens. Then it falls on 'the lens’ which is behind the cornea. Through the lens, the light falls on the retina to form a real image. To focus on objects, animals can move the lens or change its shape. Fish move their lens backward and forward to focus the image of objects on their retina. Mammals change the shape of their lens. When we have to focus on the objects at a distance our lenses become thin. Due to this the light coming from the object bends less. When we focus on nearby objects, the lenses become thicker. As a result the light coming from the object bends more and falls on the retina. The shape of lenses is changed by muscles around it. When the lens needs to be thin, the muscles relax and when the lens needs to be thick, they contract. For this reason, when you read for a long time, your muscles are contracted continuously and your eyes feel tired.

Why do our eyes feel tried if we read for a long time?