Understanding Alternating Current (AC): Principles and Rectification, Study notes of Physics

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Alternating Currents

Alternating current^ and^ voltage^ Direct^ current^ and^ voltage

Iorv ^ (^) I % ✓

steady d.c

time

TL

"" ITV Iorv on

rÉ

.

time

time ITV sinusoidal a.^ C^ Current only flows^ in

one direction^.

time

Mean value of sinusoidal^ A.^ C

r

• Io - t

• (^) t
• (^) Io - → Over^ one^ the^

current is positive for half^ cycle and

equal

and negative for other^ half^.

→ So^ Mean^ value^ of^ sinusoidal^ A^

• C (^) is zeroed average

Mean (^) power of^ sinusoidal^ A -^ C → (^) Equation of^ power dissipated in^ a^ load^ CR) (^) is (^) P= IZR In I^ = (^) Io sin ( wt) t II

I

= Io

• sin ≥ ( wt) ro.gtg.am → So^ power (1--212)^ will always be^ positive.

t^ →^ So^ mean power is^ not Zero

Ir.ms =

• vr.ms (^) = (^) I ra

Peak power

of A - C Mean power A.^ C

P.^ =^ I.^

V. (^) Ñ = T-r.ms ✗^ Vr.ms P.^ =^ I. "

R

15 =^ Ii.ms^ ✗^

R

P (^). = ¥ F =^ V-r.is

I

Relationship b/w^ peak

and mean power of^ A.c

2 Proof : § (^) = Ir.m.^ , ✗^ R^ ,^ Po^ =^

Io

• ✗ R since (^) ,^ Io^ =^ T-r.ms^ ✗^ JI Po =^ ( Ir.ms ✗^52 ]^ ✗^

R

2

Po =^ Iv.ms ✗^2 ✗^ R

P (^). = (^2) ✗ (^) (II.^ mis ✗^ '2) pp

. =^2 ×^15 → so^ peak power is twice of (^) mean (^) power or

→ Mean power is^

half of^ peak power.

→ A^ diode^ allows^ the^ current^ to^ flow^ in^ one^ direction^ only^. → (^) when (^) current is in (^) opposite direction (^) , resistance of diode becomes (^) very high and^ little^ to^ no^ current^ flows^.

→ Disadvantage^ :^ half^ -^ wave^ rectification^ only^

utilizes half

the (^) power from^ a-^ c power supply^. Rest is^ wasted^ as

heat .

diode r

← voltmeter (^) > 0 or (^) time

£ oscilloscope

Full - wave rectification

→ we (^) use a bridge rectifier , it's made up of 4 diodes A I (^) ^2

D B (^3) /
4 C

Before rectification

a voltmeter 0 or

b oscilloscope >

time

(b) 2nd^ half^ of^ the^ period . A < \

• 0 ☐ n

, s (^7)

• ° 3 4
  ↓ (^0) + / ^

> B^ R^ ✓out

^ I 0 - c r 7 time

Smoothing

→ The^ d.c^ obtained^ after^

rectification is varying.

→ (^) By connecting^ a^ capacitor in^ parallel with the^ load^ ,^ R^ ,

we can smooth^ out^ the^ d.^

a output.

Capacitor symbl^ : ÷ ◦ D i i. u (^) _ " I ◦ B C g R ,

✓out

→ The (^) degree of (^) smoothing can be increased (^) by using a capacitor of^ greater^ capacitance r r Att , time time with smaller with (^) larger

capacitor capacitor.