Q 30 (B) Signals from a transmitter of 0.1 m wavelength situated at a height of 2 m above the ground are picked up by a receiver in a radio telescope 22 m above ground at a distance of 1 km. It is desired to screen the receiver from these signals by erecting an absorbing screen 50m from the transmitter. How high must it be if the received power is to be reduced by a factor of 100? (Neglect reflections from the ground.)