A laser used for many applications of hard surface dental work emits 2780-nm wav

Question

A laser used for many applications of hard surface dental work emits 2780-nm wavelength pulses of variable energy (0-300 mJ) about 20 times per second.

Part A

Determine the number of photons in one 200-mJ pulse.

Express your answer using two significant figures.

2.8•1016

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Part B

Determine the average power of photons in one 200-mJ pulse during 1 s.

Express your answer to two significant figures and include the appropriate units.

A laser used for many applications of hard surface dental work emits 2780-nm wavelength pulses of variable energy (0-300 mJ) about 20 times per second.

Part A

Determine the number of photons in one 200-mJ pulse.

Express your answer using two significant figures.

N =

2.8•1016

photons

SubmitMy AnswersGive Up

Incorrect; Try Again; 5 attempts remaining

Part B

Determine the average power of photons in one 200-mJ pulse during 1 s.

Express your answer to two significant figures and include the appropriate units.

P =

Explanation / Answer

Here ,

wavelength = 2780 nm

frequency = 20 times per second

part A)

let the number of photons in each pulse is N

energy of 1 photon, E = h * c/wavelength

E = 6.626 *10^-34 * 3 *10^8/(2780 *10^-9)

E = 7.15 *10^-20 J

number of photons = 200 *10^-3/(7.15 *10^-20)

number of photons = 2.797 *10^18

the number of photons is 2.797 *10^18

part b)

average power = power of 1 pulse * number of pulses per sec

average power = 200 *10^-3 J * 20 1/s

average power = 4 J/s

average power = 4 W

the average power of photons is 4 W

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