at what position a candle of length 3 cm be placed infront of a convex lens so that the image of length 6cm be obtained on a screen placed at distance 30cm behind the lens? What is the focal length of the lens?
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height of the object h = 3 cm
object distance u=20 cm
radius of curvature R=50 cm
focal length f= R/2 =25 cm
image distance v = ?
size of the image h’=?
mirror formula
1/u+1/v=1/f
1/v=1/f-1/u
1/v= (1/25)-(1/20)
=(4–5)/100
=-1/100
v=-100cm
magnification m= h’/h=-v/u
m=100/20=5
5=h’/3
h’=15 cm
Image is formed at a distance of 100 cm from the mirror and is real, inverted,magnified.(-ve sign indicates the real image)
object distance u=20 cm
radius of curvature R=50 cm
focal length f= R/2 =25 cm
image distance v = ?
size of the image h’=?
mirror formula
1/u+1/v=1/f
1/v=1/f-1/u
1/v= (1/25)-(1/20)
=(4–5)/100
=-1/100
v=-100cm
magnification m= h’/h=-v/u
m=100/20=5
5=h’/3
h’=15 cm
Image is formed at a distance of 100 cm from the mirror and is real, inverted,magnified.(-ve sign indicates the real image)
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