Question

a divergent lens has a focal length of 20 cm . At what distance should an object of height 4 cm from the optical centre of the lens be placed so that its image is formed 10 cm away from the lens. Find the size of image also ? board exam question only intelligent answer by sending pictures ....

Answer 1

Given,
Focal length of divergent lens, f = −20 cm
Distance of image, v = −10 cm
Using lens formula
1f=1v−1u⇒1u=1v−1f⇒1u=1−10−1−20⇒1u=−20+10200=−10200⇒u=−20 cm
So, the object is at a distance of 20 cm from the lens(left side).

Magnification (m) is given bym=vu=himagehobject⇒−10−20=himage4⇒himage=12×4=2 cm

Answer 2

divergent lens is concave lens.
f=-20 cm
ho=4 cm
v=-10 cm
1/f=1/v-1/u
-1/u=1/f-1/v
      =1/-20-1/-10
      =-10+20/200
      =10/200
-u   =20 cm
    u=-20 cm
v/u=hi/ho
-10/-20=hi/4
       2hi=4
         hi=2cm
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