Question

Problem 11.4

An individual white LED (light-emitting diode) has an efficiency of 20% and uses 1.0 W of electric power.

Part A

How many LEDs must be combined into one light source to give a total of 3.8W of visible-light output (comparable to the light output of a 100Wincandescent bulb)?

Express your answer as an integer.

N =

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Part B

What total power is necessary to run this LED light source?

Express your answer to one significant figure and include the appropriate units.

P =

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CH 11 HW

Problem 11.4

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Answer 1

Power emitted by a sigle LED source $=1\times 0.2 W=0.2 W$

(a) Let n is the total no. of LED required,

n=3.8/0.2=19

(b) Total power necessary is= no. of LED* Power required to run a single=19*1 W=19 W