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The focal length of an optical system is the inverse of the optical power of the system. It measures how strongly the system converges or diverges light.
- A system with a positive focal length converges light, whereas a system with a negative focal length diverges light.
- The focal length is the distance between the pole of the mirror (or the optical center of the lens) and the focal point of a mirror (or lens).
- Convex mirrors are spherical mirrors with reflecting surfaces that bulge in the direction of the light source.
- Convex lenses are made by joining two spherical surfaces that bulge outward. The central portion of a convex lens is thicker than its edges.
The relationship between the position of the object (u), the position of the image (v), and the focal length of the mirror (f) is known as the mirror formula. It is given by
1/f = 1/u + 1/v
The relationship between the position of the object (u), the position of the image (v), and the focal length of the lens (f) is known as the lens formula. It is given by
1/f = - 1/u + 1/v
Ques. What is a convex lens?
Ans. The convex lens, which is relatively thick in the center and thin at the lower and upper edges, converges light rays that travel parallel to its principal axis (i.e., converges the incident rays towards the principal axis). The edges are curved outward rather than inward.
Ques. What kind of image is created by the convex lens?
Ans. Convex lenses produce real and inverted images of different sizes. Based on the position of the object, erect, virtual, and magnified images are formed.
Ques. What is the formula for finding the focal length of the convex lens?
Ans. The focal length of a convex lens can calculated by the formula
1/f = 1/u + 1/v
Where u and v are the distance of the object and image respectively from the center of the lens.
Ques. What is a convex mirror?
Ans. A convex mirror is a spherical mirror with the reflecting surface bulging out towards the light source. A convex mirror reflects light outwards and hence cannot be used to focus light.
Ques. Explain the type of image formed by the convex mirror.
Ans. A convex mirror always produces erect and diminished virtual images for all object locations.
Ques. What is a convex lens referred to as?
Ans. When parallel beams of light pass a convex lens, they converge and meet at a point on the other side. Therefore, the convex lens is also known as a converging lens.
Ques. Why is a convex lens used in cameras?
Ans. A convex lens is used in cameras to focus light to provide a clear and sharp image.
Ques. A convex lens is used to treat which type of refractive error in the human eye?
Ans. Light is converged when it passes through a convex lens. Presbyopia, hypermetropia, and aphakia can all be treated using convex lenses.
Ques. Is the focal length of a convex lens positive or negative?
Ans. The focal length of a convex lens is positive.
Ques. Which type of lens has a negative focal length?
Ans. A concave lens has a negative focal length.
Ques. Define the power of the lens.
Ans. The ability of a lens to converge or diverge light rays incident on it is referred to as its power. The power of a lens is equal to the reciprocal of its focal length. The dioptre (D) is the SI unit of power.
Ques. How is the lens power measured?
Ans. The power of a lens is measured in dioptre (D).
Ques. Define focal length.
Ans. The focal length is the distance between the pole of the mirror (or the optical center of the lens) and the focal point of a mirror (or lens). The focal point (F) of a mirror is the point at which a parallel beam of light is "focussed" after reflection in the mirror. For a convex lens and convex mirror, the focal length is taken to be positive and it is taken to be negative for concave lenses and concave mirrors.
Ques. What happens to the incident ray, which is an incident on a convex lens?
Ans. The incident rays converge towards the principal axis using a convex lens.
Ques. What are the types of mirrors?
Ans. There are two types of mirrors
- Plane mirrors
- Spherical mirrors
Ques. Is a convex mirror a transparent or opaque object?
Ans. A convex mirror is an opaque object. An opaque object does not allow light to pass through it.
Ques. When a concave lens is combined with a convex lens, what would be the quality of the image?
Ans. When a concave lens is combined with a convex lens, a sharper image is produced.
Ques. Which lens is known as a diverging lens?
Ans. Because a concave lens bends the incident rays outward, it is also known as a diverging lens.
Ques. Which type of lens is used in the human eye?
Ans. A biconvex lens is a type of convex lens present in the human eye that is responsible for the formation of real images. It works by focusing light rays towards the retina.
Ques. The lens works on which principle?
Ans. The lens works on the principles of refraction of light.
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