# 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.

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.

Manish yadav said:   7 years ago
We are not use half wave formula because in electrical method also use full wave formula because in case of electrical we are use in wark 5volt minimum value and more than,
5volt <12volt. So we are useful wave formula.
Iavg.=12volt,
Im=12*3.14÷2=18.84
Irms=18.84÷1.41=13.36.

Whis said:   5 years ago

Let me explain,
For half wave rectifier:
Vave = Vpk/π
12v = Vpk / 3.14,
12*3.14 = Vpk,
Vpk = 37.699V.

To get rms of half wave rectifer:
vrms(halfwave) = vpk/2.
Vrms(half wave) = 37.699/2.
Vrms = 18.85V.

RENJITH K N said:   2 years ago
Average voltage;
Vavg=Vmax/π=12v ----> 1.

We found rms voltage = Vrms=Vmax/2 ------> 2.

From equation 1 Vmax=Vavg x π
= 12 x π
= 12 x 3.14,
= 37.68.

Applying equation 2 Vrms=Vmax/2.
= 37.68/2 .
=18.84.

KIRAN V said:   8 years ago
Given;
V avg = 12 V.
Formula taken w.r.f to Full wave rectifier.
Vavg = 2*V max / pi.
Vmax = (V avg * 3.14)/2.
Vmax = (12 * 3.14)/2.
Vmax = 18.84 V.

Vrms = V max /sq.root of (2).
Vrms = 18.84 /1.414.
Vrms = 13.323 V.

Half Cycle means Half cycle flow in output so it is a half wave rectifier
So avverage voltage of half wave rectifier is =Vm/π.
So Vm =3.14*12,
Vm=26.64,
So rms value of HALF wave is Vm/2,
So 26.64/2=13.33.

Muhammad Nouman said:   5 years ago

Explanation:

For Half Wave Cycle Vrms = Vm/2.
and Vm = Vavg x π where π = 3.14 and Vavg = 12v,
So Vm = 12 x 3.14 = 37.68.
and
Vrms = Vm/2 = 37.68/2 = 18.84v.
Vrms = 18.84v.
(1)

If we talk a Avverage voltage of a complete sine wave then it is 0
So we need to Take Avvg Voltage =0.637*Vm.
Vm = 18.84,
RMS=Vm/√2.
18.84/1.414,
=13.33.

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.

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].