Lenses

Question 1 Define optical centre?

Question 2 Define principal focus?

Question 3 Define focal length?

Question 4 Define principal foci?

Question 5 Define first focal plane?

Question 6 Define first principal focus?

Question 7 Define second principal focus?

Question 8 What do you mean by aperture of lens?

Question 9 What are converging lenses?

Question 10 what are diverging lenses?

Question 11 Define second focal plane?

Terms used in Lenses

(1) Principal Axis

(2) Optical centre (o) : A point in or out of lens through which ray of light pass undeviated.

(3) Principal Focus (F) : A point on principal axis where all rays of light parallel to principal axis meet or appear to meet after passing through lens.

(4) Focal length (f) : The distance between the principal focus and optical centre of a lens is called focal length of lens.

(5) Principal foci : A beam of light may fall on either side of a lens therefore a lens has two principal foci.

(6) First principal foci(F_{1 )} : The position of a point on the principal axis of a lens so that the ray of light starting from this point after passing through the lens travel parallel or appear to travel parallel to principal axis.)

A vertical plane passing through first principal focus is called first focal plane.

The distance between optical centre and first principal focus is called first principal focal length.

(7) Second principal focus : The position of a point on principal axis of a lens where a beam of light parallel to principal axis meets or appear to meet after passing through the lens.

(8)Second Focal plane : A vertical line passing through second principal focus.

The distance between optical centre and second principal focus is called second principal focal length.

(9) Aperture of lens : The part of lens exposed to incident light.

A convex lens converges ray of light so it is called as converging lens.

A concave lens diverges ray of light so it is called as diverging lens.