ALERNATING CURRENT Flashcards
DEFINE ALERNATING CURRENT
An alternating current can be defined as a current that changes its magnitude and polarity at regular intervals of time.
AC VOLTAGE APPLIED TO A RESISTOR
v =VM sinω
where vm is the amplitude of the oscillating potential
difference and w is its angular frequency.
The instantaneous power dissipated in the resistor is
p = i ^ 2 R
DEFINE RMS VALUE
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
FORMULA OF I RMS
I RMS = IM /√2
AC VOLTAGE APPLIED TO AN INDUCTOR
v-[ Ldi /dt ]=0
DEFINE INDUCTIVE INDUCTANCE
The quantity w L is
analogous to the resistance and is called inductive reactance, denoted
by XL
XL= w L
The instantaneous power supplied to the inductor is
-im vm sin [2wt ] /2
AC VOLTAGE APPLIED TO A CAPACITOR
v=q/C
DEFINE CAPACITIVE REACTANCE
(1/wC) It is called capacitive reactance and
is denoted by Xc
Xc= 1/wC
AC VOLTAGE APPLIED TO A SERIES LCR CIRCUIT
L di/dt +IR +q/C=V
STUDY IMPENDENCE DIAGRAM
DEFINE RESONANCE
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.
RESONANT FREQUENCY
W0 = 1/√ LC
POWER IN AC CIRCUIT
P = I² Z cosφ
DEFINE TRNASFOMER
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.
LEARN STEP UP TRANSFORMER AND STEP DOWN TRENSFORMER
DEFINE FLUX LEAKAGE
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.
DEFINE RESISTANCE OF WINDING
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.
DEFINE EDDY CURRENTS
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.
define hysteresis
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.
