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A uniform plane wave in air is normally incident on infinitely thick slab, if the refractive index of the glass slab is 1.5 then the percentage of incident power that is reflected from the air glass interface is—
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- 0%
- 4%
- 20%
- 100%
Correct Option: B
As we know that ratio of the reflected electric field on a slab of intrinsic impedance η2 and η1 to the incidence electric field is given by following relation
| Γ = | = | (for normal incidence) | ||
| Ei | η2 + η1 |
| ⇒ | |
| √ε₁ + √ε₂ |
where √ε₂ = refractive index of medium of slab so we get
| |Γ| = | = | = | = | ||||
| Ei | η1 + η2 | 1.5 + 1 | 5 |
Power reflected = | Γ |2 Pinci
| Pref = |  |  | 2 | Pinc = | Pinc | ||
| 5 | 25 |
| Pref = | | | × 100 = 4 % | ||
| 25 |
