# Light

### Problems on light as radiation

Problem : Compute the energy density of a 2.0 mW laser beam with a diameter of 2mm.

Problem : The power per unit area incident on the earth due to sunlight is about 1.4 kW/m 2 . What is the approximate magnitude of the electric field vector on sunlight near the earth ( μ 0âÉá4Π×10-7 N.s 2 /C 2 )?

Problem : Write an expression (in SI units) for the magnetic field of a 10 MHz light wave traveling in the negative z direction and an electric field amplitude of .

Problem : Consider the following electric and magnetic waves:

 = =

Show that these waves satisfy Maxwell's equations in free space. What conditions must be satisfied?

Problem : Consider a 60W light bulb. Assume that all radiation given off is in the form of light of wavelength 650 nm. Calculate the number of photons given off per second.

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