Question

A sinusoidal electromagnetic wave of frequency 6.10

Answer 1

The magnetude of electric field of an electromagnetic wave is

Here, c is the speed of light and B is the magnetic field.

Therefore, the magnitude of electric field is

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The intensity of the laser beam is

      

Here, P is the power and r is the radius of the laser beam.

Since the diameter of the beam is 1.2 mm, its radius is 0.6 mm

  

Therefore, the intensity of the laser beam approximately is.

The maximum value of the electric field interms of intensity is

     

Here, c is the speed of light and is the permtivity of free space.

     

The maximum electric field is .

The magnitude of magnetic field is

    

The average intensity of the laser beam is one half of the maximum intensity.

  

        

       

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The intesity of the unpolarised light after passing through the first polariser becomes half.

The intensity of the beam at poiont A is

After passing through the second polarizer, the intesity of the polarised light changes as follows:

Here, is the angle between the polarising angle.

The intensity of the beam at the point B is

The intensity of the beam at point C is

If we romove the middle filter, the angle between the axis first polarisier to that of last one is

    

The intensity of the beam becomes zero.