You are asked to design a shaving mirror assuming that a person keeps it 10 cm from his face and views the magnified image of the face at the closest comfortable distance of 25 cm. The radius of curvature of the mirror would then be :

  • Option 1)

    30 cm

  • Option 2)

    24 cm

  • Option 3)

    60 cm

  • Option 4)

    -24 cm

 

Answers (1)

As we learnt in

Mirror Formula -

\frac{1}{v}+\frac{1}{u}=\frac{1}{f}


 

- wherein

u= Object distance from pole of mirror.

v= Image distance from pole of mirror.

f= focal length of the mirror.

 

 

Relation between focal length and radius of curvature -

f=\frac{R}{2}

 

- wherein

R = Radius of curvature

This is valid only for smaller angle of incidence.

i.e.paraxial rays

 

 From question v = 15 cm,  u = -10 cm

Radius of curvature R = 2f = ?

Mirror formula \frac{1}{v}+\frac{1}{u}=\frac{1}{f}=\frac{1}{15}+\frac{1}{(-10)}=\frac{1}{f}

 f = - 30 cm

\therefore    R= 2(-30) = - 60 cm 

Correct option is 3.

 

 

 

 


Option 1)

30 cm

This is an incorrect option.

Option 2)

24 cm

This is an incorrect option.

Option 3)

60 cm

This is the correct option.

Option 4)

-24 cm

This is an incorrect option.

Most Viewed Questions

Preparation Products

Knockout JEE Main April 2021 (One Month)

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Weekend Live Classes, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 14000/- ₹ 4999/-
Buy Now
Knockout JEE Main May 2021

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Weekend Live Classes, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 22999/- ₹ 9999/-
Buy Now
Test Series JEE Main May 2021

Unlimited Chapter Wise Tests, Unlimited Subject Wise Tests, Unlimited Full Mock Tests, Get Personalized Performance Analysis Report,.

₹ 6999/- ₹ 2999/-
Buy Now
Knockout JEE Main May 2022

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Live Classes, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 34999/- ₹ 24999/-
Buy Now
JEE Main Rank Booster 2021

Booster and Kadha Video Lectures, Unlimited Full Mock Test, Adaptive Time Table, 24x7 Doubt Chat Support,.

₹ 13999/- ₹ 6999/-
Buy Now
Boost your Preparation for JEE Main 2021 with Personlized Coaching
 
Exams
Articles
Questions