two lenses having focal length 20cm and -40cm are placed in contact with each other the focal length of combination will be
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p=1/f
for first lens
p1
=1/0.2
=5D
for second lens
p2
=1/-0.4
=-2.5D
combination
=p
=p1+p2
=5+(-2.5)
=2.5D
p=1/f
2.5=1/f
f=1/2.5
f=0.4m
f=40cm
for first lens
p1
=1/0.2
=5D
for second lens
p2
=1/-0.4
=-2.5D
combination
=p
=p1+p2
=5+(-2.5)
=2.5D
p=1/f
2.5=1/f
f=1/2.5
f=0.4m
f=40cm
manishmalhotra:
ma'am can i use this formula F=f1+f2 to get answer....because u did with the formula of power and the question what will be the combination of focal length..
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