Problem 28.41 ?.) 70f 10 ? Part A Constants A laser used to weld detached retina

Question

Problem 28.41 ?.) 70f 10 ? Part A Constants A laser used to weld detached retinas puts out 31-ms-long pulses of 640-nm light which average 0.67-W output during a pulse. How much energy can be deposited per pulse? (Hint see Example 27-4 in the textbook.] Express your answer to two significant figures and include the appropriate units EValueUnits Submit Request Answer Part B How many photons does each pulse contain? Express your answer using two significant figures. N- photons Submit Request Answer

Explanation / Answer

Solution:

A) Energy per pulse = Power * time

=> E = 0.67 * 31 mJ

=> E = 20.77 mJ

=> E = 21 mJ (in two significant fiugres)

B) To calculate number of photons we need energy per photon,

=> Energy per photon = h * c / wavelength

=> E = 6.62 * 10^-34 * 3 * 10^8 / 640 * 10^-9

=> E = 19.86 * 10^-26 / 640 * 10^-9

=> E = 3.1 * 10^-19 J

Number of photons = 21 * 10^-3 / 3.1 * 10^-19

N = 6.8 * 10^16 photons

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