# Homework Help: Estimate a lower limit for the number density of the electrons in the plasma

1. Nov 27, 2011

### blueyellow

1. The problem statement, all variables and given/known data

When a returning spacecraft re-enters the atmosphere, the shock wave and the friction that it generates lead to the ionisation of gas molecules just ahead of it and around it. Because of this, during the most intense phase of deceleration, radio communication signals cannot pass between the spacecraft and the ground. If the highest frequency communications band is in the region of 450 MHz, estimate a lower limit for the number density of the electrons in the plasma that surrounds a spacecraft during radio blackout..

3. The attempt at a solution

omega(of plasma)=sqrt[((N(subscript e))e^2)/((m(subscript e)) (espsilon0))

But it seems like I can't just substitue the numbers in because there is all this about the highest frequecny and the lower limit. The highest frequency won't give the lower limit because omega^2 is proportional to N(subscript e). So what do I do? Thanks if you reply.

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