# What Is The Focal Length Of The Lens In Air?

source : yahoo.com

## What is the focal length of the lens in air?

The focal length of a lens in air can be calculated from the lensmaker’s equation:

1/f = (n – 1) [1/R1 – 1/R2 + (n – 1) d / (n R1 R2)]

where

f is the focal length of the lens,

n is the refractive index of the lens material,

R1 is the radius of curvature of the lens surface closest to the light source,

R2 is the radius of curvature of the lens surface farthest from the light source, and

d is the thickness of the lens (the distance along the lens axis between the two surface vertices).

Picture:

http://upload.wikimedia.org/wikipedia/commons/thum…

For thin lenses, member containing “d” can be ignored so:

1/f = (n – 1) [1/R1 – 1/R2]

1/f = (2 – 1) [1/10 – 1/12]

1/f = 1/60

f = 60 cm.

What is the focal length of the lens in air? | Yahoo Answers – Consider a lens made with surfaces which are segments of a sphere. The first radius is 10 cm the second is 12 cm. The lens is made of a material with an index of refraction of 2.00.Basically, the focal length is the distance from the center of the lens to the focal point or the principal foci.The calculations will depend on the curvature of the lens, the lens thickness, and the refractive index of the material that the lens was made out of. Wikipedia has a great description of lens focal…( Refractive index of air-water = 1.33, refractive index for air-glass = 1.5). A biconvex lens of focal length f and radii of culvature of both the surfaces R is made of a material of refractive index n1 .

Relation between focal length and refractive index? – Answers – When the refractive index of medium is greater than the lens then what will happen to the focal length of the lens? So, a concave lens would behave like a convex lens, and a convex lens as concave lens.What is the focal length f of this lens in air (index of refraction for air is nair=1)? Suppose you are looking through a magnifier with a focal length of f, but you want to see the object you are looking at with an even greater angular magnification.The absolute index of refraction of air varies with the temperature, pressure, and humidity of the air and the The position of the lens, reduced to a single line, is the principal plane, which intersects the optical axis at It is defined as the reciprocal of the focal length of a lens in air measured in meters.

A convex lens has 20 cm focal length in air. What is focal length in… – The focal length of a lens depends on the refractive index of the material of the lens (n L ), the refractive index of the medium in which it is immersed (n m ) and the radii of curvature of the two faces of the lens (R 1 and R 2 ) according to the formula (valid for thin lenses), Sign ConventionsFocal length in air = 20 cm. Refractive index of air-water n₁= 1.33. For focal length in air, Using formula of lens. Put the value into the formula.Knowledge of the focal length of a lens is vital in the construction of all optical instruments, from spectacles to large astronomical telescopes. The object can be either a pin or a point source. Since R = 2f for a lens of glass of refractive index 1.5 placed in air, the value of f can be found.