Calculate the focal length of the thin lens shown in the figure. The points $C_{1}$ and $C_{2}$ denote the centres of curvature.

20 cm

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40 cm

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60 cm

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80 cm

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Solution

The correct option is B 40 cm
$R_{1}$ = +10 cm and $R_{1}$ = +20 cm
The focal length is given by
$\frac{1}{f} = (μ - 1) (\frac{1}{R_{1}} - \frac{1}{R_{2}}) = (1.5 - 1) (\frac{1}{10 c m} - \frac{1}{20 c m}) = 0.5 \times \frac{1}{20 c m} = \frac{1}{40 c m} o r, f = 40 c m$

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Calculate the focal length of the thin lens shown in the figure. The points C1 and C2 denote the centres of curvature.

The correct option is B 40 cmR1 = +10 cm and R1 = +20 cm The focal length is given by 1f=(μ−1)(1R1−1R2)=(1.5−1)(110 cm−120 cm)=0.5×120 cm=140 cmor, f=40 cm

Calculate the focal length of the thin lens shown in the figure. The points $C_{1}$ and $C_{2}$ denote the centres of curvature.

The correct option is B 40 cm
$R_{1}$ = +10 cm and $R_{1}$ = +20 cm
The focal length is given by
$\frac{1}{f} = (μ - 1) (\frac{1}{R_{1}} - \frac{1}{R_{2}}) = (1.5 - 1) (\frac{1}{10 c m} - \frac{1}{20 c m}) = 0.5 \times \frac{1}{20 c m} = \frac{1}{40 c m} o r, f = 40 c m$