# Electronics - Alternating Current and Voltage - Discussion

Discussion Forum : Alternating Current and Voltage - General Questions (Q.No. 5)
5.
A half-cycle average voltage of 12 V is equal to what rms voltage?
13.33 V
8.48 V
18.84 V
7.64 V
Explanation:
No answer description is available. Let's discuss.
Discussion:
24 comments Page 1 of 3.

Imax=Irms/1.414
Imax=1.57*Iav
Imax=1.57*12=18.84
Irms=18.84/1.414
Irms=13.33V

Karuppasamy kpk said:   1 decade ago
RMS value = V(peak value)*.707
V(average value)= Vpk*.637

Therefore, RMS valu =Vav*(.707/.637)

Vrms = 12*1.11 = 13.31= 13.33.

Why we are not directly taken formula for half wave rectifier.

Form factor= (rms/avg).

Avg.value = 0.636*Max.value.
Max.value = 12/0.636 = 18.86.

but,

RMS value = Max.value/1.414.
RMS value = 18.86/1.414=13.34.

So, the option is [A].

Kaneez fatima said:   1 decade ago
You all are applying formula for full cycle, but in question we asked to find rms for half cycle. If we apply formula for the half cycle answer may be wrong.

Can same formula work for rms and half cycle.

Form factor Kf = (rms value/half cycle average value).

Kf for sine wave 1.11.
rms value = 1.11X12= 13.33.

Vinod semwal said:   1 decade ago
Vpick = pai* Vavrag/2.
Vpick = 3.14*12/2.
= 18.84.

Vrms = Vpick/1.414.
= 18.84/1.414.
= 13.33 V.

Engineer Marc said:   9 years ago
This is wrong. If you use full wave formula:

Valve = 2Vpeak/3.1416 => 12 = 2Vpeak/3.14160 (Shift solve).

Vpeak = 18.8496 (full wave).

For full wave Vrms:

Vrms = Vpeak/sqrt 2 = 18.8496/sqrt 2 = 13.13 (Vrms for full wave).

The correct formula for half wave is:

Valve = Vpeak/3.1416 => 12 = Vpeak/3.1416 (Shift solve).

Vpeak = 37.6992.

For Vrms half wave its:

Vrms = Vpeak/2 => 37.6992/2 = 18.84.

SAs said:   8 years ago
For half cycle.

Effective voltage or RMS = 1.11*V average.

= 1.11*12 = 13.32 v.