Alternating Current

Question 1

What is the growth of current in a conductor I?

Answer 1

I= I₀(1-e^-RT/L)

Question 2

What is the decay of current in a conductor I=?

Answer 2

I= I₀e^-RT/L

Question 3

What is the charging of a capacitor q=?

Answer 3

q= q₀(1-e^-t/RC)

Question 4

What is the Average value of alternating current I(m)=?

Answer 4

I(m)= 2I₀/π=0.637I₀
;I(m)= mean or avg current in one half cycle 
I(o)= peak value of Ac

Question 5

What is the RMS value of alternating current ?

Answer 5

I(v)= I₀/√2=0.707I₀
;I(v)= root mean square value of current

Question 6

What is the Impedance of an AC current Z=?

Answer 6

Z= √[R²+(XL-XC)²]
; XL= Inductive reactance
XC= capacitive reactance
Z= Impedance

Question 7

What is Inductive reactance XL=?

Answer 7

XL= ωL=2πfL=2πL/T
; L= Inductance
T= Time period of AC

Question 8

What is Capacitive Reactance XC=?

Answer 8

XC= 1/ωC=1/2πfC=T/2πC
; C= Capacitance
T= Time period of AC

Question 9

What is Average power in AC circuit P(avg)=?

Answer 9

P(avg)= V(rms) i(rms) cos #= Vi/2 cos #

; cos #=Power Factor=R/Z

Question 10

What is Alternating emf E and alternating current for Pure resistive circuit =?

Answer 10

E= E₀ sin ωt
I= I₀ sin ωt
E and I are in the same phase

Question 11

What is Average power delay P in purely resistive circuit =?

Answer 11

P= E(v).I(v)

cos #= 1

Question 12

What is Alternating emf E and alternating current for Pure inductive circuit =?

Answer 12

E= E₀ sin ωt
I= I₀ sin (ωt-π/2)
I lags behind V by π/2
XL= ωL

Question 13

What is Average power delay P in purely inductive circuit =?

Answer 13

P=0

cos #=0

Question 14

What is Alternating emf E and alternating current for Pure capacitive circuit =?

Answer 14

E= E₀ sin ωt
I= I₀ sin (ωt+π/2)
I leads V by π/2
XC= 1/ωC

Question 15

What is Average power delay P in purely capacitive circuit =?

Answer 15

P=0

cos #=0

Question 16

What is Alternating emf E and alternating current for RC circuit =?

Answer 16

E= E₀ sin ωt
I= E₀/Z sin (ωt- δ)
I lags E by δ
XC=1/ωC

Question 17

What is Impedance Z of a RC circuit =?

Answer 17

Z= √R²+(1/ωC)²

Question 18

What is Alternating emf E and alternating current for LC circuit =?

Answer 18

E= E₀ sin ωt
I= E₀/Z sin (ωt- δ)
Z= XL-XC=0

Question 19

What is Alternating emf E and alternating current for LCR circuit =?

Answer 19

E= E₀ sin ωt
I= I₀ sin (ωt+#)
I lags/leads E by #

Question 20

What is Average power P at LCR circuit =?

Answer 20

P= E(v)I(v) cos #

Question 21

What is Frequency f in series resonance circuit at XL=XC, Z=R

Answer 21

f= 1/2π√LC
Q= 1/R (L/C)^-1/2
Impedance minimum , current maximum

Question 22

For parallel resonance circuit , XL=XC and Z is ?mum and I is ?mum

Answer 22

Z is maximum

I is minimum

Question 23

What is Induced emf e produced by an AC generator =?

Answer 23

e= NBA ω sin ωt= e₀ sin ωt

Question 24

What is Torque in a DC motor =?

Answer 24

Torque = NBIA sin #
; A= Area of armature
N= No of turns of conductor
B= magnetic field

Question 25

In a transformer , if energy loss =0, then what is K=?

Answer 25

K= N(s)/N(p)= E(s)/E(p)= I(p)/ I(s)

Question 26

In transformer , if energy loss !=0 then what is K=?

Answer 26

K=N(s)/N(p)=E(s)/E(p)!=I(p)/I(s)

Question 27

For step up transformer what is K=?

Answer 27

K>1

Question 28

For step down transformer what is K=?

Answer 28

K<1