Question

two thin lenses of power + 3.5Dand 2.50 are placed in contact. find tha power and focal length of the lens combination

Answer 1

power(p) =p1+p2=3.5+2.5=6.0D
focal length(f) =1/p=1/6=0.166meter
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Answer 2

Answer:

Explanation:

Power one of lens = P1 = +3.5D (Given)

Power two of lens = P2 = -2.5D (Given)

Power combination = P1 + P2

Thus,  

Power of combination = +3.5 D +(-2.5 D )

= 3.5 D -2.5 D

= 1 D

Power = 1/focal length(m)  

= 1 = 1/f

= f = 1/1

= f = 1 metre

Thus, the  f of combination = 1×100 = 100 cm

Therefore, if two thin lenses of power +3.5D and -2.5D are placed in contact then the power and focal length of the lens combination will be 100m.