Determine the rms value of the electric field of the transmitted beam

AI Thread Summary
The discussion revolves around calculating the rms value of the electric field of a transmitted beam of polarized light with an average intensity of 13.2 W/m² and a polarizer angle of 27.5°. Initially, the user attempted to apply the formula for intensity, mistakenly using the cosine squared of the angle. After several attempts, they discovered that using the cosine of the angle without squaring it yielded the correct intensity value of 11.7085 W/m². This led to the correct calculation of the rms electric field. The conversation highlights confusion regarding the application of Malus's law in the context of a homework problem.
EmoryGirl
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Homework Statement



A beam of polarized light has an average intensity of 13.2 W/m2 and is sent through a polarizer. The transmission axis makes an angle of 27.5° with respect to the direction of polarization. Determine the rms value of the electric field of the transmitted beam.


Homework Equations





The Attempt at a Solution


This is what I have done to try this problem:
I used Erms = square root of: [I(4pi * 10^-7)(3 x 10^8)]
I used I = Iocos^2theta
I = (13.2)(cos27.5)^2
I = 10.3856

According to the homework program I am using, the answer I have gotten is not correct...I am not sure what I am doing wrong. Thanks in advance!
 
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I agree with your value of I=10.4 W/m^2.
Can you post your calculation of Erms?
 
I have finally solved it! So my Erms equation was correct. My intensity was not...
Turns out what I had to do was not square the cos...
so instead of I = Iocos227.5
the equation is:
I = Iocos27.5 = 11.7085

Which I can then plug into the equation for Erms above

Thanks for your help!
 
yeah, I know...but our homework is on a computer program (CAPA), and after using 7 out of 10 tries on this problem I called a classmate and he said that he did it without the cos squared...so I tried it and it was finally marked correct!...not really sure what's going on with this problem!
 
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Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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