A student focused the image of a candle flame on a white screen by pla

1.	A student focused the image of a candle flame on a white screen by placing the flame at variousdistances from the convex lens. He noted his observation in the following table.SINO:Distance of theflamefrom the lens(cm)Distance of thescreenfrom the lens(cm)i 20 60ii 24 40iii 30 30iv 40 24v 70 12Analyse the above table and give the answers for the following questions:(a) What is the focal length convex lens?(b) Which set of observation is incorrect and why?(c) Draw ray diagram for observation (iv)(d) Find the magnification for observation (iii).
Answer» Answer: you can see, case (ii) ; here both the object and the image distances are 30cm .but we know this is possible only case when object kept at 2f,so, 2f = 30cm >f= 15cm (b) USE LENS formula for finding incorrect observations. 1v-1/u = 1/f see last observation (v) u =-15 f +15 then, 1/v = 1/15 - 1/15 = 0 = 1/co =>V = o but v 70cm is given HENCE, observation (v) is wrong. (c) obviously case 3, in this case size of image is equal to size of object due to image distance distance is equal to object distance from pole.

A student focused the image of a candle flame on a white screen by placing the flame at variousdistances from the convex lens. He noted his observation in the following table.SINO:Distance of theflamefrom the lens(cm)Distance of thescreenfrom the lens(cm)i 20 60ii 24 40iii 30 30iv 40 24v 70 12Analyse the above table and give the answers for the following questions:(a) What is the focal length convex lens?(b) Which set of observation is incorrect and why?(c) Draw ray diagram for observation (iv)(d) Find the magnification for observation (iii).

Answer»

Answer:

you can see, case (ii) ; here both the

object and the image distances are

30cm .but we know this is possible only

case when object kept at 2f,so, 2f =

30cm >f= 15cm

(b) USE LENS formula for finding incorrect

observations.

1v-1/u = 1/f

see last observation (v)

u =-15

f +15

then, 1/v = 1/15 - 1/15 = 0 = 1/co =>V = o

but v 70cm is given HENCE, observation

(v) is wrong.

of image is equal to size of object due

to image distance distance is equal to

object distance from pole.