Ohms Law

V = I * R

R = V / I

I = V /R

V = Voltage (Volts)

I = Current (Amps)

R = Resistance (Ohms)

So a current of 0.2 amps into a resisitance of 30 Ohms gives

0.2 * 30 = 6

6 Volts

 

Wavelength in metric

300 / ƒ (Mhz) = Wavelength in Meters

300 / 27.5Mhz = 10.9m

Frequency in Mhz

c / = freq in Mhz

c = speed of light

3x10⁸ / 10.9m = 27.52Mhz

Halfwave cable

300 / ƒ / 2 * Vf

ƒ = freq in Mhz

Vf = velocity value of cable used

So for RJ58 the Vf is 0.66

300 / 21.5Mhz / 2 * 0.66 = 4.604m

Wiens Law

max = 0.0029 / T

= wavelength in meters

T = temperature in Kelvin

So a blackbody which peaks at a wavelength of 20cm would have a temperature of

0.0029 / 0.2 = 0.0145Kelvin

Doppler shift

0 - 1 / 0 = v / c

0 = wavelength at which light is emitted (at rest)

1 = wavelength at which light is observed

v = the relative velocity of the source and observer

c = the speed of light

So the wavelength at which the 21cm line would be observed if the source was moving away at 500 km per second is

0.21 * (5*10⁵/ 3*10⁸) + 0.21 = 0.21035

= 21.035cm