The power of a lens is given as the reciprocal of its:
Focal length (in metres)
The power of a lens measures its ability to converge or diverge light and is defined as \(P = \dfrac{1}{f}\), where f is the focal length expressed in metres.
Because the focal length must be in metres, the unit of power is the dioptre (D), where 1 D equals 1 m-1. A shorter focal length gives a higher power, meaning the lens bends light more strongly.
Thickness is not used in this relation; a lens can be thin yet have high power if its focal length is short.
Diameter (aperture) affects how much light a lens gathers, not its power, which depends only on focal length.
Radius (of curvature) determines the focal length through the lens-maker's formula, but power itself is the reciprocal of the focal length, not of the radius.
Hence, the power of a lens is the reciprocal of its focal length in metres.
Similar Questions
Which of the following is NOT the correct use of a concave mirror?
The image formed by a concave lens for an object at infinity is:
The magnification of a concave mirror is −1. Which of the following statements is correct about the position of the object?
A ray of light enters a rectangular glass slab from air at an angle of 40 degrees to the normal. If the refractive index of glass with respect to air is 1.5 and the velocity of light in air is \(3 \times 10^{8}\) m/s, what is the velocity of light inside the glass slab?
What happens when white light passes through a glass prism?
A ray passing through the principal focus of a concave mirror will, after reflection:
A traffic surveillance camera uses a convex mirror with a radius of curvature of 2 m. Where will the image of a car located 3 m from the mirror appear?
During an experiment, a student places a candle beyond twice the focal length of a convex lens and records the image position and nature. Which of the following scenarios could result from this setup?
A student places an object 15 cm in front of a concave mirror of focal length 10 cm. If the image formed is real, what is the magnification produced by the mirror?
How does the size of atmospheric particles affect the scattering of sunlight?
Important Questions from Refraction and Reflection
A convex lens of focal length f will form a magnified real image of an object, if the object is placed.
A ray of light travelling in the direction \(\frac{1}{2} (\hat i + \sqrt 3 \hat j)\) is incident on a plane mirror. After reflection it travels along the direction \(\frac{1}{2} (\hat i - \sqrt 3 \hat j)\) The angle of incidence is:
Twinkling of stars is due to atmospheric
An optical fibre has a core material of refractive index of 1.55 and cladding material of refractive index of 1.50. The numerical aperture of the fibre is
- The refracting angle of a prism is $A$. The refractive index of the material of the prism is $\frac{1+\cos A}{\sin A}$. The angle of minimum deviation is:
