Problem 25.29 A typical helium-neon laser found in supermarket checkout scanners

Question

Problem 25.29

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 1.2 mW .

Part A

What is the amplitude of the oscillating electric field in the laser beam?

Express your answer with the appropriate units.

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Part B

What is the amplitude of the oscillating magnetic field in the laser beam?

Express your answer with the appropriate units.

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Submitted Answers for Part B

ANSWER 1: Deduction: -3%

3pT

ANSWER 2: Deduction: -3%

2.261026T

ANSWER 3: Deduction: -3%

2.26106T

Problem 25.29

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 1.2 mW .

Part A

What is the amplitude of the oscillating electric field in the laser beam?

Express your answer with the appropriate units.

E0 =

SubmitMy AnswersGive Up

Incorrect; Try Again; 3 attempts remaining

Part B

What is the amplitude of the oscillating magnetic field in the laser beam?

Express your answer with the appropriate units.

B0 =

SubmitMy AnswersGive Up

Incorrect; Try Again; 3 attempts remaining

Submitted Answers for Part B

ANSWER 1: Deduction: -3%

B0 =

3pT

ANSWER 2: Deduction: -3%

B0 =

2.261026T

ANSWER 3: Deduction: -3%

B0 =

2.26106T

Explanation / Answer

here,

wavelength, lamda = 633 nm = 633 * 10^-9m

radius of beam, r = 1.1/2 mm = 0.55mm = 0.00055m
power of beam, p = 1.2 mW = 0.0012 watts

as Intensity, I = power/area
I = P/pi*r^2
I = 0.0012/(3.14*0.00055^2)
I = 1263.36 W/m^2

also intensity is
I = Ea^2/(2*uo*c)
Where,
uo = magnatic permeability
c = speed of light in vaccum

solving for amplitude of electric field :

Eo = sqrt(2*I*uo*c)
Eo = sqrt(2 * 1263.36 * 4*3.14*10^-7 * 3*10^8)
Eo = 975.74 N/C or 978 N/C (Rounded off) or 978000 mV/m

Since Ea/Ba = c

solving for amplitude of magantic field, Ba

Bo = Eo/c
Bo = 978/(3*10^8)
Bo = 3.26*10^-6 T or 3.26 * 10^6 pT

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