Physics, asked by dkavyasri13, 1 year ago

1.an object is placed in front of concave mirror of focal length 20 Cm, the image formed is 3 times the size of the object.find the image distance.

2.A 2.5 cm candle is placed 12 cm away from a convex mirror of focal length 30 cm.find the location of the image and magnification of the image.


dkavyasri13: please answer
dkavyasri13: it is urgent
dkavyasri13: please answer
dkavyasri13: please write fast
Jahnvi97: okay!! done!
dkavyasri13: i want 2 questions answers from physics
dkavyasri13: same lesson
dkavyasri13: will u give
dkavyasri13: ill post

Answers

Answered by Jahnvi97
2
1. f = -20cm
m = -3
v = ?

m = -v/u = -3
⇒ v/u = 3
⇒ v = 3u

Using mirror formula 1/v + 1/u = 1/f
⇒ 1/3u + 1/u = 1/-20
⇒ (1+3)/3u = 1/-20
⇒ 4/3u = 1/-20
⇒ u = -(4*20)/3
⇒ u = -80/3 cm
v = 3u = -80/3 * 3 = -80cm

∴ Image distance from mirror is 80cm. It is formed in front of the mirror.

2. h = +2.5cm
u = -12cm
f = +30cm
v = ?
m = ?

1/v + 1/u = 1/f
⇒ 1/v = 1/f - 1/u = 1/30 - 1/-12
⇒ 1/v = 1/30 + 1/12
⇒ 1/v = (2+5)/60 = 7/60
⇒ v = 60/7 cm

m = -v/u = -(60/7)/(-12) = 60/(7*12) = 5/7

∴ Object distance is 60/7 from mirror. Image is virtual and erect(since v is positive). Magnification is 5/7.

dkavyasri13: hey i want another 2 questions answer
Jahnvi97: i will try!
dkavyasri13: ok ill post
Jahnvi97: Thanks dear:))
kvnmurty: there are two values of v and u for the first question...
dkavyasri13: okk
dkavyasri13: what r those
dkavyasri13: sir
kvnmurty: see my answer for those values..
dkavyasri13: ok sir
Answered by kvnmurty
3
1)
f = -20 cm                m = 3  or  - 3      either of them.

case1)  m = -v/u = -3  =>  v = 3 u          inverted image
            1/f = 1/v  + 1/u  =>  1/-20  =  1/v + 3/v = 4/v
           => v = - 80 cm

case 2)  m = -v/u = 3  =>  erect virtual  image.    v = - 3 u   
               1/-20 = 1/v - 3/v  = - 2/v       
             =>  v = 40 cm
============================

2)
u = -12 cm      h = 2.5 cm
f = +30 cm

1/f = 1/v + 1/u
1/30  = 1/v -1/12          => v = 60/7  cm     virtual image, behind the mirror.
   m = -v/u  = 5/7


dkavyasri13: sir
Jahnvi97: it is said that the image is 'formed' means it is a real image. How can image be formed if it is virtual?
dkavyasri13: yaaa
dkavyasri13: is it real
dkavyasri13: or virtual please say
kvnmurty: virtual image is also formed.... image is always said to be formed... formed means it can be virtual as well as real....
dkavyasri13: ok sir
dkavyasri13: thank u so much sir
kvnmurty: in a rear view mirror, an image is formed, then it is a virtual image..
dkavyasri13: ok sir
Similar questions