Question

what is the radius of the first zone in a zone plate of focal length 20cm for a light of wavelength 5000A°​

Answer 1

Explanation:

please explain above question

Answer 2

Answer:

The radius of the first Zone is,

$r = 3.1622777 \times 10 {}^{ - 5} m$

Explanation:

The formula relating focal length,wavelength and the radius is given as,

f = focal length = 20 cm

wavelength = 5000 A°

First Zone,n = 1

r = ?

$f = \frac{r {}^{2} }{n \times wavelength }$

$r = \sqrt{f \times 5000 \times 10 {}^{ - 10} }$

$r = \sqrt{20 \times 10 {}^{ - 2} \times 5000 \times 10 {}^{ - 10} }$

$r = \sqrt{10 \times 10 {}^{ - 9} }$

$r = 3.162277 \times 10 {}^{ - 5} m$

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