The image of candle flame placed at a distance of 40 cm from a spherical lens is formed on a screen placed on the other side of the lens at a distance of 40 cm from the lens. Identify the type of lens and write its focal length. What will be the nature of the image formed if the candle flame nature of the imge formed if the candle flame is shifted 25 cm towards the lens? Draw ray diagram to justify.

The image of candle flame placed at a distance of 40 cm from a spheric

1.	The image of candle flame placed at a distance of 40 cm from a spherical lens is formed on a screen placed on the other side of the lens at a distance of 40 cm from the lens. Identify the type of lens and write its focal length. What will be the nature of the image formed if the candle flame nature of the imge formed if the candle flame is shifted 25 cm towards the lens? Draw ray diagram to justify.
Answer» SOLUTION :Given Object DISTANCE `u=-40cm` Image distance `v=40 cm` Using lens formula `1/f=1/v-1/u=1//40-1//(-40)` or Focal length `f=+20 cm` The positive sign of focal length shows that it is a convex lens. Now Magnification `m=v//u=40//(-40)=-1` Thus the image is REAL, inverted and same size as object If candel flame is shifted 25 cm towards the lens, then `u=-(40-25)=-15cm` then `1//20=1/v-1//(-15)=1/v+1//15` or v=-60 cm `m=v//u=-60//-15=4` Thus the image will be VIRTUAL, erect and enlarged. Refer to the following diagram