Lenses

Question 1

For a convex lens:

Answer 1

If the object is outside the focus the image is real and located at the opposite side of the lens to the object. The image is inverted
If the object is inside the focus the image is virtual and is located at the same side of the lens as the object. The image is upright (erect)

Question 2

Unit of power of a lens

Answer 2

The unit of power of a lens is the per metre

Question 3

Power of two lenses

Answer 3

If two lenses of power P1 and P2 are placed in contact, the power P of the combination is given by:
P = P1 + P2

Question 4

Focal length of two lenses

Answer 4

If two lenses of focal length f1 and f2 are placed in contact the focal length f of the combination is given by:
1/f = 1/f1 + 1/f2 Where f is given a ‘+’ sign for a convex lens and a ‘-‘ sign for a concave lens

Question 5

Short sight

Answer 5

A short-sighted person can see nearby objects clearly but cannot bring distant objects into focus

Question 6

Long sight

Answer 6

A long-sighted person can see distant objects clearly but cannot being nearby objects into focus