It is desired to make an achromatic combination of two lenses L 1 L 2 made of materials having dispersive powers -1 and -2- If the combination of lenses is converging and power of L2 is more than that of L1 then

The correct option is B L _2 is convergingDispersive power ω∝1μ 1 From lens maker's formula, 1f∝ (μ 1) Power ∝μ 1 ∝1ω Thus power of L_ ...

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Standard XII

Physics

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It is desired...

Question

It is desired to make an achromatic combination of two lenses (L $_{1}$ & L $_{2}$ ) made of materials having dispersive powers $ω_{1}$ and $ω_{2}$ . If the combination of lenses is converging and power of $L_{2}$ is more than that of $L_{1}$ then

_{1}

is converging

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_{2}

is converging

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_{2}

is diverging

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none of these

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Solution

The correct option is B L $_{2}$ is converging
Dispersive power $ω \propto \frac{1}{μ - 1}$

From lens maker's formula, $\frac{1}{f} \propto (μ - 1)$

$P o w e r \propto μ - 1 \propto \frac{1}{ω}$

Thus power of $L_{2} >$ power of $L_{1}$ .

Hence if the combination is converging, the $L_{2}$ has to be converging.

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It is desired to make an achromatic combination of two lenses (L1 & L2) made of materials having dispersive powers ω1 and ω2. If the combination of lenses is converging and power of L2 is more than that of L1 then

The correct option is B L2 is convergingDispersive power ω∝1μ−1From lens maker's formula, 1f∝(μ−1)Power∝μ−1∝1ωThus power of L2> power of L1.Hence if the combination is converging, the L2 has to be converging.

It is desired to make an achromatic combination of two lenses (L $_{1}$ & L $_{2}$ ) made of materials having dispersive powers $ω_{1}$ and $ω_{2}$ . If the combination of lenses is converging and power of $L_{2}$ is more than that of $L_{1}$ then