Question

For determination of focal length the lens used isby​

Answer 1

Answer:

The following are several ways of determining the focal length of lenses. • Direct Measurement ... This method uses the follow these steps: • Solve Eq. (1) for ... The first method is by direct.

Answer 2

Explanation:

Lens Formula

Definition: The equation relating the object distance (u), the image distance (v) and the focal length (f) of the lens is called the lens formula.

Assumptions made:

The lens is thin.

The lens has a small aperture.

The object lies close to principal axis.

The incident rays make small angles with the lens surface or the principal axis.

When a lens of known focal length, f is used to find the relationship between the object distance,

u and the image distance v, the value of (1/u + 1/v) is a constant.

This constant value is equal to 1/f.

Therefore, the relationship between the object distance, the image distance and the focal length of a lens is given by the

Lens Formula: 1u+1v=1f

The lens formula may be applied to convex lenses as well as concave lenses provided the ‘real is positive’ sign convention is followed.

Table shows the sign convention for the values of object distance, image distance and focal length. All distances are measured from the optical centre of the lens.