Why can't S waves travel through Earth's liquid core? a. ...

[abern]

Why can't S waves travel through Earth's liquid core?
 
  a. Earth's liquid core is creating its own S waves.
 b. Earth's liquid core causes the seismic activity to be reflected back to its origin.
 c. Earth's liquid core absorbs the waves.
 d. Earth's liquid core is too hot and changes the wavelength of the S wave.
 e. Earth's liquid core does not have the rigidity required for shear waves to travel along.

Question 2

Why doesn't warm, dense hydrogen emit 21-cm radiation?
 
  What will be an ideal response?

[quynhmickitran]

Answer to Question 1

e

Answer to Question 2

The 21-cm radiation is another example of a forbidden line, which is an emission line from cold, neutral hydrogen gas in the interstellar medium. A hydrogen atom consists of one proton and one electron. The ground state has two energy levels, leaving two ways for the electron to spin. If the electron is spinning one way, it can flip over and spin the other way, releasing excess energy as a photon with a wavelength of 21 cm.
That transition is statistically very unlikely, and it isn't detected in laboratories on Earth because the gas is too dense and warm, and the atoms collide too often. In space, however, hydrogen atoms collide only rarely, and hydrogen atoms can go undisturbed for millions of years, allowing them to produce the 21-cm emission line.

[abern]

Excellent

[daiying98]

Thanks for the timely response, appreciate it