Uses of focal length + 50 cm and another student use a lens of - 50 discuss the nature and the find of find the power of lens
Answers
Explanation:
[Focal length of convex lens is positive and focal length of concave lens is negative. ]
Therefore,
the lens of +50cm focal length used by student is convex lens
and the lens of -50cm focal length used by another student is concave lens.
Nature of lens:
Nature of the lens having focal length +50cm:
- real and inverted OR
- virtual and erect
(it depends on the position of the object where the object is kept on the lens.)
Nature of the lens having focal length +50cm:
- virtual and erect
(size depends on the position of the object where the object is kept on the lens.)
Power of lens:
If f is expressed in metres , then power is expressed in dioptres.Thus, dioptre is the power of lens whose focal length is 1 metre. If focal length is given in centimetres then
Power = 100/f (in cm)
Power of the lens having focal length +50cm:
Power = 100/f (in cm)
= 100/ 50
= 2 D
Power of the lens having focal length -50cm:
Power = 100/f (in cm)
= 100/ -50
= -2 D
(For concave lens, power and focal length are negative.
For convex lens, power and focal length are positive.)