A lamp emits monochromatic light uniformly in all directions. The lamp is $$3$$% efficient in converting electrical power to electromagnetic waves and consumes $$100$$ W of electrical power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of $$10m$$ from the lamp will be

Question

A lamp emits monochromatic light uniformly in all directions. The lamp is $$3$$% efficient in converting electrical power to electromagnetic waves and consumes $$100$$ W of electrical power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of $$10m$$ from the lamp will be

Infinity Learn · Accepted Answer

Useful intensity,  $$I=powerareaI=100$$×(3/100)4$$π$$(10)2=34$$π×$$100Wm$$−$$2$$ Half of this intensity $$(I) belongs to electric field and half of that to magnetic field . Therefore, $$I2=14$$∈$$0E02C$$   ⇒$$E0=2I$$∈$$0C$$⇒$$E0=2$$×$$34$$π×$$10014$$π×$$9$$×$$109$$×$$3$$×$$108E0=2$$×$$3$$×$$4$$π×$$9$$×$$1094$$π×$$100$$×$$3$$×$$108=2$$×$$910=35=1.34Vm$$−$$1$$

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