Question

4. Unlike a gas, plasma can

Answer 1

Answer:

Unlike a gas, plasma can conduct electricity and respond to magnetism. That's because plasma contains charged particles called ions.

Answer 2

Answer:

a) The pressure in a traveling sound wave is given by the equation

p Pa π m x s t − − Δ = −

s x, t 6.0 nm cos kx+ 3000 rad / s t+ ( )( ) ( ) ( )

Find the (a) pressure amplitude, (b) frequency, (c) wavelength,

and (d) speed of the wave.

b) If the form of a sound wave traveling through air is

= ϕ , how much time does any given air molecule along

the path take to move between displacements s = + 2.0 nm and s = - 2.0 nm?

Solution: (a) The amplitude of a sinusoidal wave is the numerical coefficient of the sine (or

cosine) function: pm = 1.50 Pa.

We identify k = 0.9π and ω = 315 π (in SI units), which leads to f = ω /2 π = 158 Hz.

We also obtain λ = 2π/k = 2.22 m.

The speed of the wave is v = λ /k = 350 m/s.

(b) Without loss of generality we take x = 0, and let t = 0 be when s = 0. This means the

phase is φ= -π/2 and the function is s = (6.0 nm)sin(ωt) at x = 0. Noting that ω = 3000 rad/s,

we note that at t = sin-1(1/3)/ω = 0.1133 ms the displacement is s = +2.0 nm. Doubling that

time (so that we consider the excursion from –2.0 nm to +2.0 nm) we conclude that the time

required is 2(0.1133 ms) = 0.23 ms.