Question

A helium–neon laser produces a beam of diameter 1.75 mm, delivering 2.25 1018 photons/s. Each photon has a wavelength of 633 nm.

(a) Calculate the amplitude of the electric field inside the beam.

_____________ kV/m

(b) Calculate the amplitude of the magnetic field inside the beam.

______________µT

(c) If the beam shines perpendicularly onto a perfectly reflecting surface, what force does it exert on the surface?

______________nN

(d) If the beam is absorbed by a block of ice at 0°C for 1.60 h, what mass of ice is melted?

______________g

Answer #1

given :

beam diameter=d=1.75 mm

number of photons per second=n=2.25*10^18 /s

wavelength of photon=lambda=633*10^(-9) m

energy of each photon=h*c/lambda

where h=planck’s constant, c=speed of light

energy=3.1403*10^(-19) J

then power=energy of one photon*number of photon per seconds

=0.70656 W

intensity=power/area

=P/(pi*(d/2)^2)

=2.9376*10^5 W/m^2

as we know, Electric field magntiude=Emax=sqrt(2*mu*c*intensity)

=sqrt(2*4*pi*10^(-7)*3*10^8*2.9376*10^5)

=1.4883*10^4 N/C

part b:

amplitude of magnetic field=amplitude of electric field/speed of light

=4.96*10^(-5) T

part c:

force=radiation pressure*area

=(intensity/speed of light)*area

=2.3552 nN

part d:

energy given to the ice block=power*time

=0.70656*1.6*3600 J

=4069.8 J

latent heat of fusion of ice=333*10^3 J/kg

so ice melted=heat transferred/latent heat of fusion of ice

=12.222 grams

A helium–neon laser produces a beam of diameter 1.75 mm,
delivering 1.95 1018 photons/s. Each photon
has a wavelength of 633 nm.
(a) Calculate the amplitude of the electric field inside the
beam.
kV/m?
(b) Calculate the amplitude of the magnetic field inside the
beam.
µT?
(c) If the beam shines perpendicularly onto a perfectly reflecting
surface, what force does it exert on the surface
nN ?
(d) If the beam is absorbed by a block of ice at 0°C for...

A typical helium-neon laser found in supermarket checkout
scanners emits 633-nm-wavelength light in a 1.1-mm-diameter beam
with a power of 1.3 mW .
A) What's the amplitude of the oscillating
electric field in the laser beam?
B) What's the amplitude of the oscillating
magnetic field in the laser beam?

A helium-neon laser emits a 1.5-mm-diameter laser beam with a
power of 1.2 mW .
What is the amplitude of the electric field of the light
wave?
Express your answer with the appropriate units.
What is the amplitude of the magnetic field of the light
wave?
Express your answer with the appropriate units.

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