What is the focal length of concave and convex lens?
Michael King
Updated on April 05, 2026
What is the focal length of concave and convex lens?
Viva Questions
| Convex lens | Concave lens |
|---|---|
| The focal length is positive | The focal length is negative |
| Image obtained can be either real or virtual | Image obtained is always virtual |
| The light rays are converged towards the principal axis | The light rays diverge away from the principal axis |
Is the focal length of a concave lens positive or negative?
The focal length of a concave surface is negative, whereas the focal length of a convex surface is positive. Therefore, for a lens, the power of a concave and convex lens is negative and positive respectively. Whereas, for a mirror, the power of concave and convex lens is positive and negative respectively.
Does convex lens have focal length?
Convex lens have the ability to converge a parallel beam of light into a point. This point is called the focal point of the convex lens and the distance from the optical centre to the focal point is called the focal length.
What is the focal length of convex lens of focal length 30cm?
Hence, the focal length of the combination of lenses is 60 cm.
What is the focal length of above convex lens?
As we all know that the focal length of the convex lens is always positive as it behaves as a converging lens because it causes the light ray to converge at one point from the axis called as principal focus of the lens. Therefore, f1 = 30 cm.
Do convex lenses have negative focal length?
For focal length, f in lens is always taken as negative for concave and positive for convex. In case of mirror the f is taken as negative if it is in -X side i.e., is in Concave mirror and taken as positive if it is in +X side i.e., is in Convex mirror.
Can focal length of convex mirror negative?
Parallel rays of light reflected from the mirror seem to originate from the point F at the focal distance f behind the mirror. The focal length and power of a convex mirror are negative, since it is a diverging mirror.
Why concave lens has negative focal length?
For focal length, f in lens is always taken as negative for concave and positive for convex. It is taken as negative in Concave lens since image is formed in -X side of the Cartesian. In Concave mirror V is taken as positive and negative for convex mirror.
Why is focal length negative in concave lens?
The power of the lens is the reciprocal of the focal length. A concave lens is a diverging lens, so it will always have a negative focal length.
Which lens has a negative focal length?
diverging lens
A diverging lens is said to have negative focal length. A diverging lens causes exiting rays to be more divergent coming out than thay were enetering the lens. A converging lens can form a real image or a virtual image of a real object.
