Question

a student focused the image of the candle flame on a white screen using a convex lens .He noted down the positions of the candle flame , screen and the lens as given below position of candle flame = 12 cm position of the lens= 50 cm position of the screen = 88cm Q 1 find the focal length of the convex lens. Q 2 Find the position of the image of the candle flame if it is shifted towards the lens at a position of 31cm Q3 State the nature of the image formned if the candle flame is further shifetd towards the lens.. this is a 10th board question n i m nt able 2 solve it plz helppppp

Answer 1

given:
object distance=u=12-50=-38cm
image distance =v=88-50=38cm
by using lens formula:
1)1/f=1/v-1/u
1/f=1/38+1/38=2/38
therefore, f=19cm
2) v=?
if u=31-50=-19cm
f=19cm
1/f=1/v-1/u
1/v=1/f+1/u
1/19-1/19
so, V=infinity, the image will be formed at infinity as the object is kept at the focus.
3)As the object is shifted towards lens, the object  distances thus decreases and so we would see a variation in image nature,the image will be virtual,erect and magnified.

Answer 2

Answer:

i ) .  Object distance u = 12 - 50 = - 38 cm

Image distance v = 88 - 50 = 38 cm .

Since object distance is equal to image distance.

2 f = 38

= > f = 19 cm

So , focal length of object is 19 cm.

( ii ) . u = 12 - 50 = - 38 cm

It's mean candle is at focus.

= > Image will form at infinity.

( ii ) Refer to attachment for ray diagram.