ALERNATING CURRENT

Question 1

DEFINE ALERNATING CURRENT

Answer 1

An alternating current can be defined as a current that changes its magnitude and polarity at regular intervals of time.

Question 2

AC VOLTAGE APPLIED TO A RESISTOR

Answer 2

v =VM sinω
where vm is the amplitude of the oscillating potential
difference and w is its angular frequency.

Question 3

The instantaneous power dissipated in the resistor is

Answer 3

p = i ^ 2 R

Question 4

DEFINE RMS VALUE

Answer 4

To express ac power in the same form as dc power
(P = I2R), a special value of current is defined and used.
It is called, root mean square (rms) or effective current and is denoted by Irms

Question 5

FORMULA OF I RMS

Answer 5

I RMS = IM /√2

Question 6

AC VOLTAGE APPLIED TO AN INDUCTOR

Answer 6

v-[ Ldi /dt ]=0

Question 7

DEFINE INDUCTIVE INDUCTANCE

Answer 7

The quantity w L is
analogous to the resistance and is called inductive reactance, denoted
by XL
XL= w L

Question 8

The instantaneous power supplied to the inductor is

Answer 8

-im vm sin [2wt ] /2

Question 9

AC VOLTAGE APPLIED TO A CAPACITOR

Answer 9

v=q/C

Question 10

DEFINE CAPACITIVE REACTANCE

Answer 10

(1/wC) It is called capacitive reactance and
is denoted by Xc
Xc= 1/wC

Question 11

AC VOLTAGE APPLIED TO A SERIES LCR CIRCUIT

Answer 11

L di/dt +IR +q/C=V

Question 12

STUDY IMPENDENCE DIAGRAM

Question 13

DEFINE RESONANCE

Answer 13

Resonance in AC circuits is analogous to mechanical resonance, where resonance is defined to be a forced oscillation—in this case, forced by the voltage source—at the natural frequency of the system.

Question 14

RESONANT FREQUENCY

Answer 14

W0 = 1/√ LC

Question 15

POWER IN AC CIRCUIT

Answer 15

P = I² Z cosφ

Question 16

DEFINE TRNASFOMER

Answer 16

A transformer is a device used in the power transmission of electric energy. The transmission current is AC. It is commonly used to increase or decrease the supply voltage without a change in the frequency of AC between circuits.

Question 17

LEARN STEP UP TRANSFORMER AND STEP DOWN TRENSFORMER

Question 18

DEFINE FLUX LEAKAGE

Answer 18

Flux Leakage: There is always some flux leakage; that is, not all of the flux due to primary passes through the secondary due to poor design of the core or the air gaps in the core. It can be reduced by
winding the primary and secondary coils one over the other.

Question 19

DEFINE RESISTANCE OF WINDING

Answer 19

Resistance of the windings: The wire used for the windings has some resistance and so, energy is lost due to heat produced in the wire (I 2R). In high current, low voltage windings, these are minimised by using thick wire.

Question 20

DEFINE EDDY CURRENTS

Answer 20

Eddy currents: The alternating magnetic flux induces eddy currents in the iron core and causes heating. The effect is reduced by using a laminated core.

Question 21

define hysteresis

Answer 21

Hysteresis: The magnetisation of the core is repeatedly reversed by the alternating magnetic field. The resulting expenditure of energy in the core appears as heat and is kept to a minimum by using a magnetic material which has a low hysteresis loss.