ED II.    Homework  1. (due 2/11/02)

1. Show that  the minimum wavelength of radio waves that can be received at a depth of 10m below the surface of the sea is of the order of 105 m. The conductivity of sea water is approximately 4W-1m-1 ( the units are also called Siemens).

1. A copper rod is 10m long and 6 mm in diameter. Show that its resistance at 100Hz, 1 Mz and 10 GHz is approximately 6 mW, 0.15W and 15 W respectively.

1. Calculate the total force due to the radiation pressure on a plane which is perpendicular to the direction of the sunlight. The plane has an area of  1 km2  and the intensity of the sun at the surface of Earth is 1350 W/m2.

1. A Ti.Sapphire laser has a peak intensity of 1020 W/cm2, calculate the peak electric field in units of MV/m. What is the electric field on an electron which is at 1 Bohr radius from the center of the hydrogen atom?  The intensity of the sun at the surface of Earth is 1350 W/m2. What is the total power received on the surface of Earth, and compare the number with the total power received in 1 cm2 of the Ti:Sapphire laser.