Part 1 A typical helium-neon laser found in supermarket checkout scanners emits
ID: 1398319 • Letter: P
Question
Part 1
A typical helium-neon laser found in supermarket checkout scanners emits 633-nm-wavelength light in a 1.0-mm-diameter beam with a power of1.3 mW .
Part A
What is the amplitude of the oscillating electric field in the laser beam?
Answer in V/m
Part B
What is the amplitude of the oscillating magnetic field in the laser beam?
Answer in T
Part 2
A radio receiver can detect signals with electric field amplitudes as small as 350 V/m
What is the intensity of the smallest detectable signal?
answer in W/m2
Explanation / Answer
Part 1)
A)
intensity of laser = Power/area
For an electro magnetic wave ,
0.5 * 1/(3*10^8 * u0) * Em^2 = 1.3 *10^-3/(3.141 * (0.5 *10^-3)^2)
solving for Em
Em = 1117.2 N/C
the amplitude of the electric field is 1117.2 N/C
B)
magnetic field = Em/c
amplitude of magnetic field = 1117.2/3*10^8
amplitude of magnetic field = 3.724 *10^-6 T
the amplitude of magnetic field is 3.724 *10^-6 T
Part 2)
Em = 350 *10^-6 V/m
Em = 3.50 *10^-4 V/m
the intensity of the signal = 0.5 * Em^2/( c*u0)
intensity of the signal = 0.5 * 3.50 *10^-4 ^2 /( 3 *10^8 * u0)
intensity of the signal = 1.624 *10^-10 W/m^2
the intensity of the signal is 1.624 *10^-10 W/m^2