Alternating Current

Question 1

I & V phases for inductor,resistor & capacitor

Answer 1

Inductor - I lags V
Resistor - same
Capacitor - I leads V

Question 2

Why capacitor blocks DC allows AC?

Answer 2

X(c) prop 1/nyu
For DC, nyu = 0 & for AC, nyu = 50Hz
So in DC X(c) = 1/0
So it has infinite resistance

Question 3

Average power for inductor,capacitor & resistor

Answer 3

Inductor & capacitor - 0, resistor - <p> =i(m)²R/2 = i(rms)²R

Question 4

Series LCR circuit

Answer 4

V = iR + Ldi/dt + q/c
V = V(R) + V(L) + V(C)
V(RM) = imR
V(cm) = imX(c)
V(m) = im[R²+(X(c) - X(L)²]½
i(m) = V(m)/Z
Z = [R² + (X(c) - X(L)²]½

Question 5

tanO

Answer 5

Xc-Xl/R

Question 6

nyu=

Answer 6

1/2pi(LC)^1/2

Question 7

Sharpness of resonance

Answer 7

Wo/2ΔW

Question 8

Quality factor

Answer 8

1/R (L/C)^1/2

Question 9

Transformer?

Answer 9

Device used to change AV from greater value to smaller value or vis versa. It works on principle of mutual inductance

Question 10

power ratio with current and turns

Answer 10

Vs/Vp = Ns/Np = Ip/Is

Question 11

Energy loss in transformers

Answer 11

Copper, Hysteresis, eddy current and flux leakage loss

Question 12

Hysteresis loss:

Answer 12

Hysteresis loss: The AC carries the iron core through cycles of magnetisation & demagnetisation. Due to this, energy is lost in the form of heat. It can be minimized by using core material having narrow hysteresis loop.

Question 13

Eddy current loss:

Answer 13

Eddy current loss: The alternating Magnetic flux induces eddy currents in the iron core which leads to some energy loss in form of heat. This can be minimized by using laminated iron core.

Question 14

Copper loss:

Answer 14

Copper loss: Some energy is lost due to heating of copper wires used in primary & sec windings. It can be minimized by using thick copper wires of low resistance.

Question 15

Flux leakage

Answer 15

The magnetic flux produced by the primary may not fully passthrough the secondary. Some of the flux may leak into air. This can be minimized by winding the primary & secondary coils over 1 another.

Question 16

For Lcr circuit, power is?

Answer 16

Neither 0 nor max but in btn

Question 17

When surface is ||, net Flux is

Answer 17

0

Question 18

Transformer applications

Answer 18

Transmission, power generation, electronic equipments

Question 19

Flux is ______ for closed surfaces

Answer 19

outward normally

Question 20

Resonate/angular frequency is

Answer 20

Omega

Question 21

When frequency of supply is equal to natural frequency, it is due to

Answer 21

Resonance

Question 22

power factor

Answer 22

cosΦ = R/Z

Question 23

resonance circuit is also called

Answer 23

acceptor circuit

Question 24

define quality factor

Answer 24

ratio of voltage drop across inductor at resonance to applied voltage across the source

Question 25

Maximum power dissipation occurs at

Answer 25

Resonance