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# Remember the Basics?Answers to RF Cafe Quiz #22

All RF Cafe Quizzes make great fodder for employment interviews for technicians or engineers - particularly those who are fresh out of school or are relatively new to the work world. Come to think of it, they would make equally excellent study material for the same persons who are going to be interviewed for a job. Bonne chance, Viel Glück, がんばろう, buena suerte, удачи, in bocca al lupo, 행운을 빕니다, ádh mór, בהצלחה, lykke til, 祝你好運. Well, you know what I mean: Good luck!

Note: Some material based on books have quoted passages.

This quiz challenges your recollection of the basics.

1. How much power is dissipated by the ideal 10 μH inductor in the circuit to the right?

d) 0 mW

Ideal reactive components (inductors and capacitors) do not dissipate power - only resistive components dissipate power. Ideal inductors and capacitors store and release energy in the form of magnetic and electric fields, respectively, with 100% efficiency (no losses). Real-life inductors and capacitors have a resistive property (the ratio of which is referred to as "Q", or quality factor), so they do actually dissipate some power.

2. How much current flows through the guy at the right?

d) 0 A

Since there is not a complete path, current cannot flow through the body.

3. In the figure for Q2, what voltage would be measured

between the guy's hand and ground?

c) 0 V

The voltage supply as shown has no established ground reference, so any place you connect a resistive (< ∞) path sets the ground (0 V) point. Even a high impedance input voltmeter has a finite resistance so it would set the ground reference, although it might take a while for any residual charge to bleed off.

4. What is the name of the newly fabricated 4th type of passive component?

a) Memristor

Memristors - a contraction of "memory resistors" - are passive two-terminal circuit elements that exhibit a fixed a functional relationship between the time integrals of current and voltage. The property is called memristance. The existence of memristors was predicted in 1971 in paper published by Professor Leon Chua, of UC Berkeley.

5. What is the significance of a component's self-resonant frequency?

b) It is the frequency about which its reactance changes numerical sign (+ to -, or - to +)

Due to the non-ideal characteristics of capacitors and inductors, there are parasitic elements in series and parallel in the complete equivalent circuit models. Capacitors actually have inductive properties in series that, together with the intended capacitance, create a point of frequency resonance where the impedance is purely resistive. Below the self-resonant frequency (SRF), the capacitor measures as a capacitor (a negative reactance) and above the SRF, it measures as an inductor (a positive reactance). Inductors have parasitic capacitance in parallel that causes them to measure as inductive (+) below the SRF, and capacitive (-) above it.

6. Which type of filter is called "maximally flat" in amplitude response?

a) Butterworth

Butterworth filters have a transfer function that is numerically optimized to produce the maximum rate of rejection out of band while producing no amplitude ripple in the passband. It turns out to be a very simple equation.

7. What is the approximate melting point of common lead-free solder (e.g., SnAg3.0Cu0.5)?

b) 220 °C (~430 °F)

Use of lead-free solder was mandated by global insistence on conforming to practices that reduce the amount of heavy metals (e.g.; lead) in waste products. Lead from solder in electronics represents a very small percentage of overall lead in the world (compared to batteries, x-ray shielding, plumbing, etc.), but it was an easy target. Lead solders like the common 60Sn/40Pb compound melt at much lower temperatures (~190°C = 370 °F) than lead-free types. SnAg3.0Cu0.5 (~220 °C = 430 °F) is the mix recommended by JEITA for reflow while iNEMI recommends SnAg3.9Cu0.6 (~ same melting point as SnAg3.0Cu0.5). The down side is that the higher melting temperatures require much more energy usage, so while pollutants in landfills go down, pollutants in the atmosphere go up ).

8. What is the gain of the opamp configuration to

the right?

c) -1

The gain for an inverting configuration opamp is:

G = - Rfeedback/Rinput

9. What is the gain of the opamp configuration to

the right??

a) 2

The gain for a non-inverting configuration opamp is:

G = 1 + Rfeedback/Rinput

10. Which type of transistor is shown to the right ?

a) Enhancement Mode N-Channel MOSFET

A simple tip for interpreting the symbol for a MOSFET is that the arrow tip always points to the N-type material (true for all semiconductors), and the broken line for the channel suggests that is needs to be completed (enhanced) to permit current flow.