A student focused the image of a candle flame on a white screen using a convex lens.He noted down the position of the candle,screen and the lens as under, Position of candle=12.0 cm Position of convex lens=50.0 cm Position of screen=88.0 cm a)What is the focal length of the convex lens? b)Where will the image be formed if he shifts the candle towards the lens at a position of 31.0 cm?
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Answered by
46
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.
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.
Answered by
6
Answer:
( i ) . Object distance u = 50 - 26 = 24 cm
Image distance v = 74 - 50 = 24 cm .
Since object distance is equal to image distance.
2 f = 24
= > f = 12 cm
So , focal length of object is 12 cm.
( ii ) . u = 50 - 38 = 12 cm
It's mean candle is at focus.
= > Image will form at infinity.
( ii ) Refer to attachment for ray diagram.
Attachments:
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