## A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.

Subscribe to our Youtube Channel - https://you.tube/teachoo

Last updated at April 26, 2020 by Teachoo

Subscribe to our Youtube Channel - https://you.tube/teachoo

Transcript

NCERT Question 11 A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram Since the focal length of a concave lens is negative ∴ Focal length = f = −15 cm Also, A concave lens forms a virtual, erect image Hence, image distance will be negative Image distance = v = −10 cm Let the object distance = u Using lens formula, 1/𝑓 = 1/𝑣 − 1/𝑢 1/𝑓 − 1/𝑣 = (−1)/𝑢 (−1)/𝑢 = 1/𝑓 − 1/𝑣 1/𝑢 = 1/𝑣 − 1/𝑓 1/𝑢 = (−1)/10 − 1/((−15)) 1/𝑢 = (−1)/10 + 1/15 1/𝑢 = (−3 + 2)/30 1/𝑢 = (−1)/30 u = − 30 cm 1/𝑢 = (−3 + 2)/30 1/𝑢 = (−1)/30 u = − 30 cm Hence, object is placed 30 cm infront of the lens. The Ray Diagram looks like

NCERT Questions

NCERT Question 1

NCERT Question 2

NCERT Question 3

NCERT Question 4

NCERT Question 5

NCERT Question 6

NCERT Question 7

NCERT Question 8

NCERT Question 9

NCERT Question 10

NCERT Question 11 You are here

NCERT Question 12

NCERT Question 13

NCERT Question 14

NCERT Question 15

NCERT Question 16

NCERT Question 17

Class 10

Chapter 10 Class 10 - Light - Reflection and Refraction

About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.