Astronomers often speak of light from a distant source as being red-shifted, whe

Question

Astronomers often speak of light from a distant source as being red-shifted, where the measured wavelength is made longer than that emitted by the source by some interfering effect (typically a Doppler effect). Consider the electromagnetic spectrum, and explain why astronomers might use this to describe these wavelength measurements. Astronomers often speak of light from a distant source as being red-shifter, where the measured wavelength is made longer than that emitted by the source by some interfering effect (typically a Doppler effect). If someone described a wavelength measurement as being blue-shifted instead, what can you say about original wavelength and frequency of the wave before the blue-shifting occurred? Estimate the amount of energy from sunlight that your face absorbs over your entire lifetime. (This intensity is lower than the 1360 W/m^2 used in Example 34.2 because of atmospheric absorption, scattering, and other factors.) Find the intensity of the electromagnetic wave described in each case: An electromagnetic wave with a. a wavelength of 710 nm and a peak electric field magnitude of 2.5 V/m and b. an angular frequency of 7.5 times 10^18 rad/s and a peak magnetic field magnitude of 10^-10 T. An electric field E vector = (23.0 i cap - 55.0 j cap + 17.0 k cap) V/m and a magnetic field B vector = (5.25i cap + 4.05j cap + 6.00k cap) n T are measured location in free space. What is the Poynting vector at this location? Show that the electric and magnetic field are perpendicular to each other at this location.

Explanation / Answer

Ans. (42)

Electromagetic wave intensity is given by
I = 1/2*c*e0*E0^2

and it is magnetic field peak value is B0 then we know

E0 = c*B0

(a)
Given E0 = 2.5 v/m

I = 1/2*3*10^*8.854*10^-12*2.5^2

I = 8.30*10*-3 W/m^2

(b)
Given B0 = 10^-10 T

E0 = c*B

= 3*10^8*10^-10

E0 = 3*10^-2

I = 1/2*3*10^8*8.854*10^-12*(3*10^-2)^2

I = 1.19*10^-6 W/m^2

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