Browse by Stream
QnA
Home
QnA
Go To Your Study Dashboard

Get Answers to all your Questions

header-bg qa
  • Home
  • NCERT
  • If a parabolic reflector is 20 cm in diameter and 5 cm deep, find the focus.

1. If a parabolic reflector is 20 cm in diameter and 5 cm deep, find the focus.

Answers (1)

best_answer

Let the parabolic reflector open towards the right.

So, the equation for parabolic reflector will be,

y^2=4ax

Now, since this curve will pass through the point (5,10) if we assume origin at the optical centre,

So, 

10^2=4a(5)

a=\frac{100}{20}=5

Hence, the focus of the parabola is,

(a,0)=(5,0).

Alternative Method: 

As we know, on any concave curve

f=\frac{R}{2}

Hence, focus 

f=\frac{R}{2}=\frac{10}{2}=5.

Hence, the focus is 5 cm right to the optical centre.

Posted by

Pankaj Sanodiya

View full answer

Crack CUET with india's "Best Teachers"

  • HD Video Lectures
  • Unlimited Mock Tests
  • Faculty Support
cuet_ads

Similar Questions

Trending Articles/News

anam-khan

CBSE Class 12 Chemistry Exam Analysis 2025: Paper 'moderately difficult' but well balanced
anam-khan

CBSE Class 12 board exam still once a year; 20 lakh expected to appear in 2026 from February 17
anam-khan

CBSE board exams twice a year from 2025-26; 2 subject groups, 'better of two marks' in draft policy

Latest Question