Question 169: Semiconductors and Logic Gates

Question

A red $$LED$$ emits light at $$0.1$$ watt uniformly around it. The amplitude of the electric field of the light at a distance of $$1$$ $$m$$ from the diode is :

Accepted Answer

Intensity of light at a distance r, $$I = {P \over {4\pi {r^2}}}$$ [P = power]
Again, if the amplitude of the electric field is E
0
then $$I = {1 \over 2}c{ \in _0}E_0^2$$
$$	herefore$$ $${P \over {4\pi {r^2}}} = {1 \over 2}c{ \in _0}E_0^2$$
or, $${E_0} = \sqrt {{P \over {2\pi c{ \in _0}{r^2}}}} $$
$$ = \sqrt {{{0.1} \over {2 	imes 3.14 	imes (3 	imes {{10}^8}) 	imes (8.85 	imes {{10}^{ - 12}}) 	imes {1^2}}}} $$
= 2.45 V/m

Answer

$$5.48$$ $$V/m$$

Answer

$$7.75$$ $$V/m$$

Answer

$$1.73$$ $$V/m$$

Answer

$$2.45$$ $$V/m$$

Semiconductors and Logic Gates

A red $LED emits light at 0.1 watt uniformly around it. The amplitude of the electric field of the light at a distance of 1 m$ from the diode is :

Choose the correct answer: