Spherical lenses are lenses formed by binding two spherical transparent surfaces together. There are two basic kinds of spherical lenses:
Concave lens: The lenses formed by binding two spherical surfaces such that they are curved inward are known as concave lenses.
Convex lens: The lenses formed by binding two spherical surfaces bulging outward are known as convex lenses.
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What Is Lens Formula?
Convex lenses are also known as converging lenses since the rays converge after falling on the convex lens, while concave lenses are known as diverging lenses as the rays diverge after falling on the concave lens. Images formed by these lenses can be real or virtual depending on their position from the lens and can have different sizes too. The image distance can be calculated with the knowledge of object distance and focal length with the help of the lens formula. In optics, the relationship between the distance of an image (i), the distance of an object (o), and the focal length (f) of the lens are given by the formula known as the Lens formula. The Lens formula is applicable for convex as well as concave lenses. These lenses have negligible thickness. It is an equation that relates the focal length, image distance, and object distance for a spherical mirror. It is given as,
i= distance of the image from the lens
o= distance of the object from the lens
f= focal length of the lens
The lens formula is applicable to all situations with appropriate sign conventions. This lens formula is applicable to both the concave and convex lenses. If the equation shows a negative image distance, then the image is a virtual image on the same side of the lens as the object. If this equation shows a negative focal length, then the lens is a diverging lens rather than the converging lens. This equation is used to find image distance for either real or virtual images.
Let’s learn more about the lens formula and magnification in this video
Calculating magnification with the help of the lens formula:
The magnification of a lens is defined as the ratio of the height of an image to the height of an object. It is also given in terms of image distance and object distance. It is equal to the ratio of image distance to that of object distance.
Where m= magnification
h’= height of the image
h = height of an object
v is the image distance
u is the object distance
Power of Lens
The power of a lens is the measure of the degree of convergence or divergence of the light rays falling on it. The degree of convergence or divergence depends upon the focal length of the lens. Thus, we define the power of the lens as the reciprocal of the focal length of the lens used. It is given as,
Where f is the focal length of the lens used. SI unit of power is Dioptre (D). The power of the concave lens is negative, while the power of the convex lens can be positive.
Watch the video and learn more about longitudinal magnification
Frequently Asked Questions – FAQs
What is a convex lens?
What is meant by the power of a lens?
What is the relationship between the focal length and the power of a lens?
What is the SI unit for the power of a lens?
What is meant by the focal length?
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