15.Astudent has to project a three times magnified image of a candle f

1.	15.Astudent has to project a three times magnified image of a candle flame on a wall. Name thetype of lens (converging/diverging ) required for the purpose. If the candle flame is at adistance of 6 m from the wall, find the focal length of the lens.3
Answer» Converging lens or Convex lens should be used by the user to project the image of candle on the wall as he wants it to be three times magnified. Reason:In Convex lens, when object is placed between F and C , the image will be formed beyond C .Nature of Image :--> magnified, real and inverted.hi=3hoImage distance= object distance + 6v=6+uwe know that magnification=m=v/um=v/u-3=v/u[since image is magnifed three times ]-3=6+u/u-3u=6+u4u=-6u=-6/4u=-1.5 mv=6-(-1.5)v=7.5mby using lens formula,1/f =1/v-1/u1/7.5 +1/1.5=1/f10/75+10/15=1/f10+50/ 75=1/f∴ f=75/60=1.25mThus, Focal length of a given convex lens is 1.25m

15.Astudent has to project a three times magnified image of a candle flame on a wall. Name thetype of lens (converging/diverging ) required for the purpose. If the candle flame is at adistance of 6 m from the wall, find the focal length of the lens.3

Answer»

Converging lens or Convex lens should be used by the user to project the image of candle on the wall as he wants it to be three times magnified.

Reason:In Convex lens, when object is placed between F and C , the image will be formed beyond C .Nature of Image :--> magnified, real and inverted.hi=3hoImage distance= object distance + 6v=6+uwe know that magnification=m=v/um=v/u-3=v/u[since image is magnifed three times ]-3=6+u/u-3u=6+u4u=-6u=-6/4u=-1.5 mv=6-(-1.5)v=7.5mby using lens formula,1/f =1/v-1/u1/7.5 +1/1.5=1/f10/75+10/15=1/f10+50/ 75=1/f∴ f=75/60=1.25mThus, Focal length of a given convex lens is 1.25m

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