Question

student focus the image of candle flame on screen of convex lens. he noted down; position of candle= 12 cm . 2)position of convex lens = 50 cm, 3)position of screen= 88 cm. find::- focal length of convex lens ii where image be formed if we shift candle at 31 cm. iii what will be the nature of image formed if e further shift the candle towards lens. draw ray diagram of image in third part

Answer 1

A1) u=-(50-12) cm =-38 cm

& v=(88-50) cm=38 cm

using lens formula

1/v -1/u=1/f

1/38 -(-1/38)=1/f

1/f=1/19 

f=19 cm

2) now 

u=-(50-31) cm=-19 cm

so,

1/v-1/u=1/f

1/v=0

v=infinity

3) Now if candle is moved towards

lens the image will be magnified & 

virtual & erect