PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics
Problem
A pair of astronauts has landed on the Moon. They rely on two different systems to gather information:
• A radio transceiver in each helmet sends and receives voice signals to a lunar‐orbiting relay satellite.
• A portable seismic source produces mechanical vibrations in the lunar soil so that subsurface layers can be mapped by a sensor aboard the same satellite.
The Moon has essentially no atmosphere, but its solid surface can support mechanical vibrations.
Use this context to analyze how the two kinds of waves propagate from the surface to the satellite located directly overhead at an altitude of 110km above the surface.
(a) Describe the fundamental difference between mechanical waves and electromagnetic waves with respect to whether a material medium is required for their propagation.
(b) Explain why the voice radio signal can travel from an astronaut’s helmet antenna to the relay satellite even though no atmosphere is present.
(c) The seismic source generates sound waves within the lunar soil. Give two distinct reasons the satellite’s sensor will not receive these waves.
(d) Discuss how the mutually perpendicular electric and magnetic fields in an electromagnetic wave enable it to transport energy through empty space, whereas the absence of particles prevents the same for mechanical sound waves.