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Subelement G6
Circuit Components
Section G6A
Resistors; capacitors; inductors; rectifiers; solid-state diodes and transistors; vacuum tubes; batteries
What is the minimum allowable discharge voltage for maximum life of a standard 12 volt lead-acid battery?
• 6 volts
• 8.5 volts
10.5 volts
• 12 volts

$10.5$ volts is the minimum allowable discharge voltage for a standard 12 volt lead acid battery to retain maximum cell life.

Discharging below this level can cause changes in the chemical nature of the cell which are irreversible, which can damage or destroy the cell.

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What is an advantage of the low internal resistance of nickel-cadmium batteries?
• Long life
High discharge current
• High voltage
• Rapid recharge

High discharge current is an advantage of the low internal resistance of nickel-cadmium (NiCd) batteries. This makes them great to use in portable electronic devices and tools which require high current flow.

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What is the approximate junction threshold voltage of a germanium diode?
• 0.1 volt
0.3 volts
• 0.7 volts
• 1.0 volts

$0.3$ Volts is the approximate junction threshold voltage of a germanium diode.

This threshold is the voltage over which the diode can conduct significant current. Different materials have different junction threshold voltages, so the value for each diode is determined by the properties of the material(s) used in its construction.

For example, a diode made of silicon has a junction threshold voltage of about $0.7$ Volts.

Silly Hint:

G for Germanium is about $\frac{3}{10}$ ($0.3$ V) of the way through the alphabet while S for Silicon is about $\frac{7}{10}$ ($0.7$ V) of the way through the alphabet.

Sillier hint
Not the most PC tip, but associate German with Third Reich. : German, 3... Germanium == $0.3$

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Which of the following is an advantage of an electrolytic capacitor?
• Tight tolerance
• Much less leakage than any other type
High capacitance for a given volume
• Inexpensive RF capacitor

An advantage of electrolytic capacitors is that they have high capacitance for given volume.

These capacitors are often used in power supplies for AC voltage filtering.

They are polarized and must be placed in the circuit in the proper orientation, as reverse-voltages can cause catastrophic (explosive) failure. Bad electrolytic caps can swell and leak the electrolyte out the vent grooves notched in the top, appearing as a crusty substance. Also the electrolytic capacitors may have large variations in capacitance due to their method of manufacture.

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What is the approximate junction threshold voltage of a conventional silicon diode?
• 0.1 volt
• 0.3 volts
0.7 volts
• 1.0 volts

The approximate junction threshold voltage of a conventional silicon diode is $0.7$ volts.

This threshold voltage is the voltage where the diode can start to conduct the greater part of the current. The material a diode is made from is a significant factor in what the threshold voltage will be. For example, the germanium diode has a junction threshold of about $0.3$ volts.

Silly Hint:

S for Silicon, S for Seven. Also, the letter S is about $\frac{7}{10}$ (0.7 volts) of the way through the alphabet.

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Which of the following is a reason not to use wire-wound resistors in an RF circuit?
• The resistor's tolerance value would not be adequate for such a circuit
The resistor's inductance could make circuit performance unpredictable
• The resistor could overheat
• The resistor's internal capacitance would detune the circuit

One reason not to use wire-wound resistors in an RF circuit is that the resistor's inductance could make the circuit performance unpredictable.

The construction of a wire wound resistor is VERY similar to that of an inductor. So in situations where extra inductance may be an issue (such as RF circuits), they are not a good component choice.

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What are the stable operating points for a bipolar transistor used as a switch in a logic circuit?
Its saturation and cutoff regions
• Its active region (between the cutoff and saturation regions)
• Its peak and valley current points
• Its enhancement and depletion modes

The stable operation points for a bipolar transistor used as a switch in a logic circuit are its saturation and cut-off regions. The saturation region acts as a good "full on" switch position, whereas the cut-off region acts as a good "full off" switch position.

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What is an advantage of using a ferrite core toroidal inductor?
• Large values of inductance may be obtained
• The magnetic properties of the core may be optimized for a specific range of frequencies
• Most of the magnetic field is contained in the core
All these choices are correct

(1) What advantage does a toroid core provide as opposed to a straight core?

(2) What advantage does a ferrite core provide as opposed to a powdered iron core?

Toroids have become popular because the amount of magnetic flux that leaks outside of the core itself is low, which makes it more efficient and it radiates less electromagnetic interference.

Additionally, toroid cores are a closed loop. In a straight core the magnetic field has to go pretty far from one end to enter at the other. This means that the toroid will typically produce a larger inductance.

Finally, by varying the size and thickness and characteristics of the ferrite itself, you can optimize a ferrite toroid for different frequencies.

Silly Hint: the TOROIDAL inductor gives you the TOTAL package.

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Which of the following describes the construction of a MOSFET?
• The gate is formed by a back-biased junction
The gate is separated from the channel with a thin insulating layer
• The source is separated from the drain by a thin insulating layer
• The source is formed by depositing metal on silicon

A MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is constructed so that the gate is separated from the channel with a thin insulating layer. The metal oxide is used in a thin layer to keep the gate from being in direct contact with the channel. This way the principal current flow is between the drain and the source, but not through the gate.

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Which element of a triode vacuum tube is used to regulate the flow of electrons between cathode and plate?
Control grid
• Heater
• Screen grid
• Trigger electrode

The control grid is the element of a triode vacuum tube used to regulate the flow of electrons between cathode and plate.

Hint: to “regulate” is to “Control” or remember that a triode tube has a control grid.

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What happens when an inductor is operated above its self-resonant frequency?
• Its reactance increases
• Harmonics are generated
It becomes capacitive
• Catastrophic failure is likely

Inductors have what is called a “Parasitic element” to them. Almost any electrical component you can think of has parasitic elements. Even the leads of a resistor have a parasitic behavior to them.

In our case, the parasitic element is capacitance. Capacitors are created by having metal objects in close proximity to each other, usually with a di-electric component separating them. Inductors are just a large amount of metal wire wrapped around a base. The wires interact with each other, creating a usually negligible capacitive effect, but an effect at that. If the inductor is sitting on a ground plane, the coil will even have a capacitive effect between the wires and the ground plane it is sitting upon.

Inductors have a frequency in which they are usable with maximum benefits. Manufacturers of the inductors will usually state this range, in addition to what is called the SRF.(Self Resonant Frequency) This frequency is the point at which the capacitive components resistance equals the ideal inductance. Basically, Resistance equals Inductance at this point. There are good graphs showing this with an easy internet search.

To combat this, manufacturers will make their inductors with a SRF one decade above the intended frequency range (10x the frequency).

Once the inductor hits the point of its SFR, the inductive component drops to basically zero. What’s left is essentially a capacitor.

Hint: Pushing an inductor too far makes it a capacitor (the opposite)

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What is the primary purpose of a screen grid in a vacuum tube?
To reduce grid-to-plate capacitance
• To increase efficiency
• To increase the control grid resistance
• To decrease plate resistance

The screen grid insulates/isolates the control grid from the plate which helps counteract the Miller effect by reducing the grid-to-plate capacitance.

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Why is the polarity of applied voltages important for polarized capacitors?
• Incorrect polarity can cause the capacitor to short-circuit
• Reverse voltages can destroy the dielectric layer of an electrolytic capacitor
• The capacitor could overheat and explode
All these choices are correct

All of these choices are correct

Consider a common type of polarized capacitor: an electrolytic capacitor. Electrolytic capacitors must be connected in the way specified, since the dielectric, usually a thin film of metal oxide, rapidly breaks down when current in the wrong direction is applied.

When the dielectric breaks down, the two "plates" of the capacitor can short out, generating a large amount of current to go through the capacitor and causing massive heating. These rapid and violent changes can result in a venting of hot liquid, or sometimes in dangerous explosions.

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Which of the following is an advantage of ceramic capacitors as compared to other types of capacitors?
• Tight tolerance
• High stability
• High capacitance for given volume