Quiz Day Friday: Electronics and Electrical

As Friday returns, so does Quiz Day Friday — curiously captivating quizzes from top members of the Electro-Tech-Online community members including: 3vO,DerStrom, Ian Rogers, Pommie, Roman Black, Reload Ron, JimB, MrAl, and ericgibbs. Electro-Tech-Online is an electrical engineering membership forum where you can ask questions and get answers from your fellow engineers on topics such as radio communications, microcontrollers, PCB design, and more.

And there’s more where this came from as you can see from the previous week’s quizzes.

Quiz V1.0 on General Electronic and Electrical Engineering
Quiz V2.0 on Common Engineering Abbreviations
Quiz V3.0 Electronic and Electrical Engineering – Intermediate
Quiz V4.0 Computer History
Quiz V5.0 C Programming Language
Quiz V6.0 Electronics and Radio

This week’s quiz is brought to you by Electro-Tech-Online well-known member MrAl,  A member since 2008, MrAl is an “ex-EE” (is there any such thing as an ex EE??) with over 30 years of experience and has contributed to over 9,000 conversations. He has also authored articles on Electro-Tech-Online including: Biot Savart Part 1 about computing the magnetic field outside of a finite straight wire using Biot Sav; Diode Log and AntiLog Circuit Derivations; and Indirect Measurement of the Current Draw of a Device.

We list the questions below just to give you a heads-up, but you’ll find the complete quiz — with the multiple choice options — HERE.  Of course, you could always just jot your answers down on a piece of paper and match them up with the formal quiz. Go ahead. Live dangerously.

Quiz V6.0 Electronics and Electrical – Intermediate

1. For a motor that has a torque proportional to current and an output torque of 100 Newton meters at a current of 1 ampere, if the current is increased to 3 amperes what is the torque?
2. For two lossless transformers both with voltage ratios equal to 1 are wired with primaries in parallel and secondaries in series and are driven by a voltage source with internal impedance of 20 ohms. What is the output impedance across the two secondaries?
3. The following equation represents a sine wave: E=Vpk*sin(w*t+Theta). What does Theta represent? E=Vpk*sin(w*t+Theta)?
4. The formula for the 3db cutoff frequency of a low pass filter made from a resistor R in series with a capacitor C and driven by an AC voltage source and taking the output from the junction of the resistor and capacitor to ground is:
   F=1/(2*pi*R*C)
   Using a resistor value of 1k, find the capacitor value that causes a 3db cut in the gain at a frequency F of 1 kHz. Approximate the capacitor value to three significant decimal places.
5. A perfect square wave varies in amplitude between +1 volts and -1 volts. The harmonics present in this wave are…?
6. In a liquid crystal display, the internal light source initially gets polarized but in order to obtain the brighter light levels something else is done to the light next. What happens to the light next?
7. In an AC circuit, a coupling capacitor can help to pass the AC component of the current but block the DC component. The reason this can work is because…?
8. If we had an extremely large collection of 1000 ohm resistors (billions) where any one value could vary anywhere from plus 10 percent to minus 10 percent and we chose at random 100 of them and connected all 100 together in parallel, what would be the approximate tolerance of the resulting 10 ohm resistor?
9. We have a resistor in series with a capacitor driven by an input step voltage E and taking the output (referenced to ground) from the junction of the capacitor and resistor.
   The state vector differential equation for this circuit is: x’ = E/RC-x/RC (see diagram) where x is the state variable, x’ is the time derivative of the state variable, E is the input voltage, RC is the product of the resistor value times the capacitor value. Euler’s Method is a technique for solving this equation numerically, and is given by: x[n+1]=x[n]+h*x'[n] (see diagram) where x[n] is the current value of the state variable, x[n+1] is the next solution for the state variable, x'[n] is the time derivative calculated at n, h is the time increment. With R=1k and C=100uf and with the initial state x=0 and using a time increment of 1 millisecond, calculate the value of x (the capacitor voltage) at the time t=10 milliseconds using Euler’s Method where E is the unit step forcing function, and approximate the solution to 3 significant decimal places. The value of x (the capacitor voltage) at t=10ms is…?
10. In the drawing for the transformer, each winding has the same number of turns and is wound on a lossless core as shown. If the input terminals T1 and T2 are driven with a source with internal impedance equal to 100 ohms. What is the impedance looking into the terminals T3 and T4?