Inductance Interview Questions 

Two series RCL circuits have the same resonant frequency. Circuit A has an inductance of .45 H and circuit B has an inductance of .20H. Determine the ratio of the capacitances of the circuits, CA/CB

A. .44
B. .20
C. 5.0
D. 1.6
E. 2.3

Why in a circuit, inductors and resistors are taken as a single resistive component (add up when they are in series ), and why inductances are taken on imaginary axis aren't their values real.

An inductor coil has a resistance of 5.0 ohms and an inductance of 120 mH. If a voltage of 12V is applied, what time will it take for the coil current to reach its maximum value and what will this current maximum be?

thanks heaps!

Given the a resistors resistance, an inductors inductance, and an average power at a certain linear frequency, how would I go about finding the resonant angular frequency. I didn't provide the numbers because this IS a homework problem, and I do not want people to think I am trying to get others to do my work. I just need help as I am stuck and don't know where to go next!

I'm trying to solve the question below:

Consider an LCR circuit arranged in series such that L, C, and R are the values of inductance, capacitance and resistance respectively. The voltage across the capacitor satisfies the ordinary differential equation:

(LC)d²Vc/dt² + (RC)dVc/dt + Vc = V(t)

where V(t) is the supply voltage.

for LC = 1/2 and RC = 1, use the method of Laplace transforms to solve the equation above when the supply voltage is given by:

V(t) = Vo(d(t-b) + 2H(t-b))

where b > 0 and the circuit is initiated according to Vc(0) = 1, Vc'(0) = -1. What are the values of Vc(t) at t = b/2 and t = 2b?

I've been trying to do this question for some time now and haven't got anywhere! Any help would be greatly appreciated!

Thanks :)

Malcom

A square loop of wire with a small resistance is moved with constant speed from a field free region into a region of uniform B field (B is constant in time) and then back into a field free region to the left. The self inductance of the loop is negligible.

http://i36.photobucket.com/albums/e12/li...

Answer True or False:

1) Upon entering the field, a clockwise current flows in the loop.

2) When entering the field the coil experiences a magnetic force to the right.

3) When leaving the field the coil experiences a magnetic force to the right.

4) While the loop is entirely in the field, the emf in the loop is zero.

An RLC series circuit has a resistance of R = 325 ohms, an inductance L = 0.300 mH, and a capacitance C = 33.0 nF.
a) What is the resonant frequency?
b) If the capacitor breaks down for peak voltages in excess of 7.0 X 10^2 V, what is the maximum source voltage amplitude when the circuit is operated at the resonant frequency?

I found the resonant frequency by using X of L = X of C and solving for the frequency. But I'm not sure if that is even right. I am confused as to what equations to use. If you can show me the work and equations you use to get the answers, that would be greatly appreciated and I'll get you 10 points.

The answers to a and b are:
a) 3.18 X 10^5 rad/s and 50.6 Hz
b) 2.4 KV

I could sure use help understanding how to get those answers. Thank you very much.

3) If the number of turns is tripled for an inductor of fixed length and fixed cross sectional area, what happens to its inductance??

a) stays same
b) triples
c) becomes 9 times the orig value
d) decrease by a factor of 3
e) decrease by a factor of 9

4) A 33 m-h inductor has a current going through it that is increasing at a rate of 2.3 A/s. What is the magnitude of the indeuced emf in this coil?

a) 33 mV
b)76 mv
c)13mv
d)175 mv
e)2.5 v


I got C for 3 and D for 4 . . . am I right, if not please explain, thanks

RLC Series Circuit. In the study of an electrical circuit consisting of a resistor, capacitor, inductor, and an electromotive force we are led to an initial value problem of the form
L(dI/dt) + RI + (q/c) = E(t); This is eq. 20
q(0) = q-not,
I(0) = I-not,
where L is the inductance in henrys, R is the resistance in ohms, C is the capacitance in farads, E(t) is the lectromotive force in volts, q(t) is the charge in coulombs on the capacitor at time t, and I = (dq/dt) is the current in amperes. Find the current at time t if the charge on the capacitor is initially zero, the initial current is zero, L = 10 H, R = 20 Ohms, C = (6260)^-1 F, and E(t) = 100 V. [Hint: Differentiate both sides of the differential equation in (20) to obtain a homogeneous linear second-order equation for I(t). Then use (20) to determine dI/dt at t =0.

I have the answer and it is I(t) = (2/5)(e^-t)sin25t
I need the steps to work this problem out. Thanks in advance.

3) If the number of turns is tripled for an inductor of fixed length and fixed cross sectional area, what happens to its inductance??

a) stays same
b) triples
c) becomes 9 times the orig value
d) decrease by a factor of 3
e) decrease by a factor of 9

4) A 33 m-h inductor has a current going through it that is increasing at a rate of 2.3 A/s. What is the magnitude of the indeuced emf in this coil?

a) 33 mV
b)76 mv
c)13mv
d)175 mv
e)2.5 v

I understand the basic workings of a transformer,the questions on them really difficult. This is one of the questions - I'd really like a guided explaination on how to tackle it.

An audio-frequency tranformer, designed to operate at frequencies as low as 20Hz is used to transform the 5ohm resistance of a secondary load into a reflected resistance that equals the 75ohm output resistance of the voltage generator attached to the primary coil. The magnetic core of the transformer is a toroid of average radius 5cm, cross-sectional area 30cm-squared, and relative permeability = 500. Calculate the minimum number of primary and secondary turns that must be wound on the core so as to achieve impedance matching, whilst having a primary inductance that presents an impedance of at least 150ohm. [You may assume perfect coupling and zero coil resistance)

Thanks

The symbol L for inductance was chosen to honor Heinrich Lenz (1804-1865

A square loop of wire with a small resistance is moved with constant speed from a field free region into a region of uniform B field (B is constant in time) and then back into a field free region to the left. The self inductance of the loop is negligible.

http://i36.photobucket.com/albums/e12/li...

Answer True or False:

1) Upon entering the field, a clockwise current flows in the loop.

2) When entering the field the coil experiences a magnetic force to the right.

3) When leaving the field the coil experiences a magnetic force to the right.

4) While the loop is entirely in the field, the emf in the loop is zero.

Take a look at figure 4 here http://www.imagesco.com/articles/picstep... Why are the 4050 hex buffers needed? Is it because the PIC outputs are open drain/collector. So if I try to build a similar circuit but using an AT89C2051 I can simply ignore these buffers right?

Moreover on that same schematic, TIP120 darlingtons are used. Now in another good resource on the subject ( figure 4 http://www.parex.org/weblog/archive/0000... ) the circuit uses IRF542 mosfets. Which would you use and why? ie what are advantages etc. And do mosfets include the inductance protection diodes as the TIP120's do.

Thanks a lot.

b) The voltage across the resistor is a function of the frequency according to equation

V(r) = R/[sqrt { R^2+ (2*pi*f*L - 1/ 2*pi*f*C)^2}]V

where R is resistance in ohms, L is inductance in henrys (H) and C is capacitance in farads (F). Write a program to plot the voltage across the resistor as a function of the frequency when L=0.1mH, C=0.25nF, R=50?, and V=10mV. Let f vary from 500kHz to 1500kHz with a step of 10kHz. Use legend, graph title, and labels for x-axis and y-axis. Turn on the grid. At what frequency does the voltage across the resistor reach the peak?
Please NOTE that while doing this MATLAB is giving error which is:-
>> R=50;
>> C=0.25*10^(-9);
>> V=10*10^(-3);
>> L=0.1*10^(-3);
>> f=500:10:1500;
>> V=((R/sqrt(R^2+(2*pi.*f*L-1/2*pi.*f*C)^2...
??? Error using ==> mpower
Matrix must be square.