Official PYQ · 2017Set 2 · Q55Plane Waves and PropertiesNAT2 marks

GATE EC 2017 Set 2 Q55 — Plane Waves and Properties

The permittivity of water at optical frequencies is $1.75 \varepsilon _0$ . It is found that an isotropic light source at a distance $d$ under water forms an illuminated circular area of radius $5$ m, as shown in the figure. The critical angle is $\theta _c$ .

The value of $d$ (in meter) is _______________

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Answer: 4.2:4.4

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Published 10 Oct 2026

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