Presentation is loading. Please wait.

Presentation is loading. Please wait.

The Effective Value of an Alternating Current (or Voltage)

Similar presentations


Presentation on theme: "The Effective Value of an Alternating Current (or Voltage)"— Presentation transcript:

1 The Effective Value of an Alternating Current (or Voltage)
© David Hoult 2009

2

3

4

5

6

7 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

8 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

9 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

10 The R.M.S. Value of an Alternating Current (or Voltage)

11

12 If an a.c. supply is connected to a component of resistance R, the instantaneous power dissipated is given by

13 If an a.c. supply is connected to a component of resistance R, the instantaneous power dissipated is given by power = i2 R

14

15

16 The mean (average) power is given by

17 The mean (average) power is given by
mean power = (mean value of i2) R

18 The mean value of i2 is

19 I2 The mean value of i2 is 2

20 The square root of this figure indicates the effective value of the alternating current

21 The square root of this figure indicates the effective value of the alternating current
r.m.s. = root mean square

22

23 I Irms = 2 where I is the maximum (or peak) value of the a.c.

24 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

25 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.

26 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

27 We have been considering a sinusoidal variation of current (or voltage)

28 We have been considering a sinusoidal variation of current (or voltage)

29 We have been considering a sinusoidal variation of current (or voltage)
For this variation, the r.m.s. value would be

30 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


Download ppt "The Effective Value of an Alternating Current (or Voltage)"

Similar presentations


Ads by Google