3. A helium-neon laser emits a monochromatic beam of linearly polarized sinusoid

Question

3. A helium-neon laser emits a monochromatic beam of linearly polarized sinusoidal plane electromagnetic wave with an average intensity of 4.5 kW/m2 and with wavelength 633 nm. (a) What is the average energy density of the beam? (b) What is the value of Ems and B (c) What is the frequency of this wave? (d) How long it takes to complete one cycle of this wave? (e) Suppose the beam is cylindrical, what is its diameter if it has an average power of 15.0 mW? () Express the electrical field as a function of time, t (9) If this beam is transmitted in water, what will be its wavelength? (h) What is the propagating speed of this wave in water? Deduce that the frequency remains the same ()Suppose a 2.0-nC static charge is available in the beam, what is the maximum electric force it experiences? Note: Required constants should be identified and found out by the student.

Explanation / Answer

a) average energy density = average intensity/ c = 4.5x10^3/(3*10^8)=1.5*10^-5J/cu. m

b)Erms=Brms=1.1098*uavg/2= 8.32 * 10 ^-6 J/cu. m

c) frequency = c/ wavelength = 3*10^8/ (633*10^-9)=4.7*10^14 Hz

d)Time period = 1/frequency= 1/(4.7*10^14)=2.12*10^-15 s= 2.2 femto seconds

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