the filament of the lamp is 80 cm from a screen and converging lens forms on image of it on the screen,magnified three times.find?
a )the distance of the lens from the filament
b)the focal length of the lens
Answers
Answered by
0
Sun is at a huge distance in comparison with the focal length of the lens.
Hence, the objective distance can be considered at infinity.
Hence the image will be formed at its focus.
Consider the following situation:

Understand the angle subtended by the common tangents with Sun and its image are vertically opposite angles. Hence they are equal to each other and is equal to 0.5 degrees.
Thus the angle BOA = 0.5 degrees.
Also the distance OA=OB=100 cm
Hence the distance AB is
AB=x260(2πr)r=100 cmx=0.5∘AB=0.5360(2×227×100)AB=0.873 cm
Hence, the objective distance can be considered at infinity.
Hence the image will be formed at its focus.
Consider the following situation:

Understand the angle subtended by the common tangents with Sun and its image are vertically opposite angles. Hence they are equal to each other and is equal to 0.5 degrees.
Thus the angle BOA = 0.5 degrees.
Also the distance OA=OB=100 cm
Hence the distance AB is
AB=x260(2πr)r=100 cmx=0.5∘AB=0.5360(2×227×100)AB=0.873 cm
Similar questions