The Effective Value of an Alternating Current (or Voltage) © David Hoult 2009
If the two bulbs light to the same brightness (that is, they have the same power) then it is reasonable to consider the current Iac to be (in some ways) equivalent to the current Idc
If the two bulbs light to the same brightness (that is, they have the same power) then it is reasonable to consider the current Iac to be (in some ways) equivalent to the current Idc The simple average value of a (symmetrical) a.c. is equal to
If the two bulbs light to the same brightness (that is, they have the same power) then it is reasonable to consider the current Iac to be (in some ways) equivalent to the current Idc The simple average value of a (symmetrical) a.c. is equal to zero
The R.M.S. Value of an Alternating Current (or Voltage)
If an a.c. supply is connected to a component of resistance R, the instantaneous power dissipated is given by
If an a.c. supply is connected to a component of resistance R, the instantaneous power dissipated is given by power = i2 R
The mean (average) power is given by
The mean (average) power is given by mean power = (mean value of i2) R
The mean value of i2 is
I2 The mean value of i2 is 2
The square root of this figure indicates the effective value of the alternating current
The square root of this figure indicates the effective value of the alternating current r.m.s. = root mean square
I Irms = 2 where I is the maximum (or peak) value of the a.c.
The r.m.s. value of an a.c. supply is equal to the direct current which would dissipate energy at the same rate in a given resistor
The r.m.s. value of an a.c. supply is equal to the direct current which would dissipate energy at the same rate in a given resistor We can use the same logic to define the r.m.s. value of the voltage of an alternating voltage supply.
The r.m.s. value of an a.c. supply is equal to the direct current which would dissipate energy at the same rate in a given resistor We can use the same logic to define the r.m.s. value of the voltage of an alternating voltage supply. V Vrms = 2 where V is the maximum (or peak) value of the voltage
We have been considering a sinusoidal variation of current (or voltage)
We have been considering a sinusoidal variation of current (or voltage)
We have been considering a sinusoidal variation of current (or voltage) For this variation, the r.m.s. value would be
We have been considering a sinusoidal variation of current (or voltage) For this variation, the r.m.s. value would be equal to the maximum value