Inductance Interview Questions 

So im suppose to calculate the energy stored in a magnetic field at time t= 90 ms

It's an LR curcuit with Inductance L = 2.4 Henry, resistance R = 30 Ohms, An emf of 12 volts is connected to the circuit at T=0.

I also need to Calculate the Voltage Across the Inductor at Time T= 90ms


I started useing the EQ i = io e^ (-t/row), but that gives current not Energy.

A lossy transmission line with no reflections has per kilometer parameters R = 100 W, G=0,C=10^-9 F, and L = UNKNOWN. At x=0, the voltage waveform on the line is v(t)
=10cos(10*pi*t)
. At a point x=300 m, the voltage on the line is found to lag the current by 20 degrees.
Compute the following: (a) the per kilometer inductance L; (b) the total inductance for 800 m section of this line.

I did part (a) and I got 1.19x10^-3 H. I am not sure if that is correct. I don't know how to do part (b). Can you please show your work on how to solve this problem? Thanks.

ive finished most of the code for the following program, here's the code:

#include <iostream>
#include <cmath>

using namespace std;

int main(void)
{
double X, Z, angle, f, R, L, C;
const double PI = 4.0 * atan(1.0);
cout << "SERIES RLC CIRCUIT CALCULATION \n";

cout << "Please enter values for frequency, resistance, inductance, and capacitance. \n";
cout << "This program will calculate the impedance and the phase angle of the circuit. \n";

do
{
cout << "Enter the value of the frequency in hertz: ";
cin >> f;
if (f < 0)
{
cout << "Frequency must be non-negative \n";
}
else if (f == 0)
{
cout << "Zero frequency entered. Program terminated. \n";
cout << "Goodbye. \n";
return 0;
}
}
while (f < 0);
do
{
cout << "Enter the value of the resistor in ohms: ";
cin >> R;

if (R < 0)
{
cout << "Resistance must be non-negative. \n";
}
}
while (R < 0);

do
{
cout << "Enter the value of the inductor in henrys: ";
cin >> L;

if (L < 0)
{
cout << "Inductance must be non-negative. \n";
}
}
while (L < 0);

do
{
cout << "Enter the value of the capacitor in farads: ";
cin >> C;

if (C < 0)
{
cout << "Capacitance must be positive. \n";
}
}
while (C < 0);

cout << "\n";

X = (2*PI*f*L) - (1/ (2*PI*f*C));
Z = sqrt((R*R) + (X*X));

angle = (atan(X/R))*(180/PI);

cout << "The impedance of this series RLC circuit is " << Z << " ohms \n";
cout << "The phase angle is " << angle << " degrees \n\n";


fflush(stdin);
getc(stdin);

return 0;
}


everything calculates properly but my problem is that i want it to continue to loop after the user finishes making a calculation. so after it displays the impedance and phase angle it should go back to where it asks the user to enter the frequency. what should i do and where should i put in a extra command?

thaNks

An RL circuit in which the inductance is L = 9.00 H and the resistance is R = 5.00 is connected to a 20.0 V battery at t = 0.

a) What energy is stored in the inductor when the current is 0.500 A? 1.125 J (I got this part which was relatively easy)

b) At what rate is energy being stored in the inductor when I = 1.00 A?

c) What power is being delivered to the circuit by the battery when I = 0.500 A?

Now for b and c, I was using the equation P=I^2*R=[(Blv)/R]^2 which does not really work at all for some reason on RL circuits.
Also, P=I^2R=I^2Rexp(-2Rt/L)...

Part a) I used U=1/2LI^2
I'm just very confused, can any one help please?

Let the current I2 = I0e^-(at) be dependent on time where I0 = 9A, a = 3s^-1, and t is measured in seconds.

If the mutual inductance between the coil and the solenoid is 9 mH, what is the magnitude of emf induced in the coil at t = .5 s? Answer in units of mV.


I know that the answer is mutual inductance X time rate. But, I don't know how to find the time rate which is dI/dt.

How can I find this time rate to find the answer?

Thank you for your help.

1) The resonant frequency of an RCL circuit is 1.3 kHz, & the inductance is 7.0 mH. What is the resonant frequency (in kHz) when the value of the inductance is 1.5 mH?

2) A 40.0 microF capacitor is connected across a 60.0-Hz generator. An inductor is then connected in parallel with the capacitor. What is the value of the inductance if the rms currents in the inductor & capacitor are equal?


Any help would be greatly appreciated! Thanks!

Capacitor...the capacitor has an initial charge, q0 = 30 µC, what is the value of the capacitance, C?
A capacitor carrying charge q0 with capacitance C, and a solenoid with inductance L are connected as shown in Figure 1. At time t = 0 the switch is
closed. At time t the charge on the capacitor is q(t) and the current through the circuit is i(t).

1)If the solenoid has inductance L = 1.00 H, and the energy in the oscillations is E0 = 4.5 µJ, what is the maximum value, i0, of the current through the circuit?
2)Given that the capacitor has an initial charge, q0 = 30 µC, what is the value of the capacitance, C ?
3)What is the frequency, f, of the oscillations?

A circuit has inductance L=0.2H, resistance R=400ohm, capacitance C=5x10^-4F, voltage source = 12V. Find the equation for current i.

Using K as the constant, write an equation that expresses: The length (W) of a radio wave varies jointly as the square root of the inductance (L) and the capacitance (C).

A W = kLC
B W = sqrtC/KL
C W = k/sqrt(LC)
D W = k * LC
E W = k * sqrt(LC)
F W = KL/sqrtC

A sensitive electronics device of resistance 175 Ohm is to be connected to a source of e.m.f. by a switch. The device is designed to operate with a current of 36 mA, but to avoid damage to the device the current can rise to no more than 4.9 mA in the first 58 micro-seconds after the switch is closed. To protect the device, it is connected in series with an inductor.

a. What e.m.f must the source have?

b. What inductance is required?

c. What is the time constant?

A circuit has an inductance L=0.5H, a resistance R=1000ohm, and a capacitance C=5.6x10^-6F. Find the equation for the current i if the voltage source is 12V given that i=0 and q=0 at t=0.

Hi, i'm looking for a clear explanation as to what transformers are. What i know is that they are something to do with coils of wire round a core of a metal, there's some kind of inductance there, and it all has to do with an electro motive force, and what in god's name has the ratio of primary to secondary turns have to do with anything ?
Anyone who can explain these things will get 5 whole points, or whatever the amount of points you get for getting the answer right is.
Thanks.

My teacher gave me this problem and I still can't find the answer. Please help me with this one or at least give me some idea so I could somehow give him a response.

v(t): voltage
i(t): current
V: amplitude of the sine wave
L: inductance
w: omega
f: frequency

w = 2f Pi
v(t) = V sin(wt)
V sin(wt) = L di/dt
=> v(t) = L di/dt

i(wt = alpha) = 0 ; 0=< alpha < Pi

Solve the differential equation i(t)|alpha = ?


In other words, find i(alpha, t) : the time dependence of the current i over the angle alpha or how does the current i change when the angle alpha change over time)

What would be the worst case power dissipation for an ideal inductance?

Is the ans. zero? If so, why, and if not why?

Please help.

Thanks.

an LR series has a variable inductor with inductance

L(t) = 1- 1/10t , 0<t<10
0 , t>10

R=0.2 ohm
E(t)=4V
i(0)= 0

find i(t)...