Question

if two lenses of focal length 20cm and -10 cm are used in the combination what will be the combimed power of tje lens​

Answer 1

Answer:

Explanation:

1 or 2 meter optical bench.

Illuminated object-box.

Object-image device for measuring focal length of positive lenses.

Screen, for locating real images.

Reference pointer, for locating virtual images.

Lenses, f = -20 cm.

Assorted simple lenses.

Wide focusing range telescope and holder, for locating images.

Ramsden eyepiece, or other achromatic eyelens (optional).

Short focal length achromatic lens for microscope objective.

Small specimen on microscope slide (a reticle will do.)

Answer 2

Question :

• Two lenses of focal length 20cm and -10 cm are used in the combination what will be the combined power of the lens​.

Given :

• f  ' = 20 cm = 0.2 m
• f " = - 10 cm = 0.1 m

[ in order to convert cm into m divide by 100 ]

To find :

• Combined power of the lens

Solution :

As per the formula ,

$\leadsto \mathtt{P = P' + P" }$

$\leadsto \mathtt{P = \dfrac{1}{f'} + \dfrac{1}{f"} }$

$\leadsto \mathtt{P = \dfrac{1}{0.2 } - \dfrac{1}{0.1 } }$

$\leadsto \mathtt{P = \dfrac{1-2}{0.2 } }$

$\leadsto \mathtt{P = \dfrac{-1}{0.2 } }$

$\leadsto \mathtt{P = - 5 D }$

Extra Information :

• The focal length of the concave lens is negative
• The focal length of the convex lens is positive