A sinusoidal voltage can be described by the equation:
v(t) = V_{M} sin (ωt + Φ) or v(t) = V_{M} cos (ωt + Φ)
where  v(t)  Instantaneous value of the voltage, in volts (V). 
V_{M}  Maximum or peak value of the voltage, in volts (V)  
T  Period: The time taken for one cycle, in seconds  
f  Frequency – the number of periods in 1 second, in Hz (Hertz) or 1/s. f = 1/T  
ω  Angular frequency, expressed in radians/s ω = 2*π*f or ω = 2*π / T. 

Φ  Initial phase given in radians or degrees. This quantity determines the value of the sine or cosine wave att = 0.  
Note: The amplitude of a sinusoidal voltage is sometimes expressed as V_{Eff}, the effective or RMS value. This is related to V_{M}according to the relationship V_{M}=√2V_{Eff, }or approximately V_{Eff }= 0.707 V_{M} 