Ch5 - Refraction in Lenses

A lens is defined as ‘a transparent refracting medium bounded ______________'

• by two spherical surfaces

• two plane surfaces

• one spherical and one plane surface

• either two spherical surfaces or one spherical and one plane surface

The ray of light passing through the optical center _____

• deviates away from the principal axis

• passes undeviated

• refracts parallel to the principal axis

• reflects backwards

Where must a point source of light be placed in front of a convex lens so as to obtain a parallel beam of light?

• At the first focus

• At the second focus

• At the optical centre

• at the first centre of curvature

An object is placed between F1 and optical center a convex lens, the image formed will be _____

• Real, inverted and beyond 2F2

• On the same side as the object, behind it

• On the same side as the object, in front of it

• at the focus

Principal axis is defined as ‘a line joining the _____

• two foci

• two centres of curvature

• centre of curvature and focus

• centre of curvature and optical centre

An object is placed at a distance of 25 cm from a convex lens of focal Length 10 cm. The image formed is real, inverted and ______.

• enlarged

• diminished

• of the same size as object

• none of the above

What is the unit of power of a lens?

• watt

• diopter

• decibel

• phon

How does the power of a lens change if its focal length is doubled?

• power doubles

• power is halved

• power is unaffected

• power decreases to one-fourth

If the magnification produced by a lens is - 0.5, the correct statement is

• the lens is concave

• image is virtual

• image is magnified

• image is real and diminished

For an object placed at a distance 20 cm in front of a convex lens, the image is at a distance 20 cm behind the lens. The distance between the two foci of the lens is _______

• 20 cm

• 10 cm

• 15 cm

• 40 cm