Correct option is B
Correct Option: (b) 33.3 cm, 3D
Focal length of the convex lens
Focal length of the concave lens
Effective Focal Length
The formula for the effective focal length (FFF) of two lenses in combination is:
1F=1f1+1f2\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2}
Substitute the values:
1F=120+1−50\frac{1}{F} = \frac{1}{20} + \frac{1}{-50}
Power of the Doublet
The power (PPP) of a lens is given by:
P=100F(in cm)P = \frac{100}{F (\text{in cm})}
Substitute F=33.33cmF = 33.33 \, \text{cm}F=33.33cm:
P=10033.33=3DP = \frac{100}{33.33} = 3 \, \text{D}
Final Answer:
Effective focal length: 33.33 cm
Power: 3D
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