CH 3

Question 1

In a reverse biased PN-junction, which current carriers cause leakage current?

Answer 1

The minority carriers

Question 2

The action of a PN-junction during breakdown can be explained by what two theories?

Answer 2

Zener effect and avalanche effect

Question 3

Which breakdown theory explains the action that takes place in a heavily doped PN-junction with a reverse bias of less than 5 volts?

Answer 3

Zener effect

Question 4

What is the doping level of an avalanche effect diode when compared to the doping level of a Zener-effect diode?

Answer 4

The doping level of an avalanche effect diode is lower

Question 5

During avalanche effect breakdown, what limits current flow through the diode?

Answer 5

An external current-limiting resistor.

Question 6

Why is electron flow with the arrow in the symbol of a Zener diode instead of against the arrow as it is in a normal diode?

Answer 6

Because Zener diodes are operated in the reverse bias mode.

Question 7

What is the main difference in construction between normal PN junction diodes and tunnel diodes?

Answer 7

The amount of doping.

Question 8

What resistance property is found in tunnel diodes but not in normal diodes?

Answer 8

Negative resistance.

Question 9

When compared to the ordinary diode, the tunnel diode has what type of depletion region?

Answer 9

The tunnel diode has a very narrow depletion region

Question 10

In the tunnel diode, the tunneling current is at what level when the forbidden gap of the N-type material is at the same energy level as the empty states of the P-type material?

Answer 10

Minimum.

Question 11

The varactor displays what useful electrical property?

Answer 11

Variable capacitance

Question 12

When a PN junction is forward biased, what happens to the depletion region?

Answer 12

The depletion region decreases.

Question 13

When the reverse bias on a varactor is increased, what happens to the effective capacitance?

Answer 13

Capacitance decreases.

Question 14

The SCR is primarily used for what function?

Answer 14

The SCR is primarily used for switching power on or off.

Question 15

When an SCR is forward biased, what is needed to cause it to conduct?

Answer 15

A gate signal.

Question 16

What is the only way to cause an SCR to stop conducting?

Answer 16

The forward bias must be reduced below the minimum conduction level.

Question 17

The TRIAC is similar in operation to what device?

Answer 17

SCR.

Question 18

When used for ac current control, during which alternation of the ac cycle does the TRIAC control current flow?

Answer 18

During both alternations.

Question 19

What type of bias is required to cause an LED to produce light?

Answer 19

Forward bias

Question 20

When compared to incandescent lamps, what is the power requirement of an LED?

Answer 20

Very low

Question 21

In a common anode, seven-segment LED display, an individual LED will light if a negative voltage is applied to what element?

Answer 21

The cathode.

Question 22

What is the resistance level of a photodiode in total darkness?

Answer 22

Very high

Question 23

What type of bias is required for proper operation of a photodiode?

Answer 23

Reverse bias

Question 24

What is a typical light-to-dark resistance ratio for a photocell?

Answer 24

1:1000.

Question 25

What semiconductor device produces electrical energy when exposed to light?

Answer 25

Photovoltaic cell.

Question 26

The UJT has how many PN junctions?

Answer 26

One

Question 27

The area between base 1 and base 2 in a UJT acts as what type of common circuit component?

Answer 27

Variable resistor.

Question 28

The sequential rise in voltage between the two bases of the UJT is called what?

Answer 28

A voltage gradient.

Question 29

What is the normal current path for a UJT?

Answer 29

From base 1 to the emitter.

Question 30

What is one of the primary advantages of the FET when compared to the bipolar transistor?

Answer 30

High input impedance.

Question 31

The FET and the vacuum tube have what in common?

Answer 31

Voltage controls conduction.

Question 32

The base of a transistor serves a purpose similar to what element of the FET?

Answer 32

Gate.

Question 33

Q33. What are the two types of JFET?

Answer 33

N-channel and P-channel.

Question 34

The source and drain of an N-channel JFET are made of what type of material?

Answer 34

N-type material.

Question 35

What is the key to FET operation?

Answer 35

Effective cross-sectional area of the channel.

Question 36

What is the normal current path in an N-channel JFET?

Answer 36

From source to drain.

Question 37

Applying a reverse bias to the gate of an FET has what effect?

Answer 37

Source-to-drain resistance increases.

Question 38

The input and output signals of a JFET amplifier have what phase relationship?

Answer 38

They are 180 degrees out of phase.

Question 39

When compared to the JFET, what is the input impedance of the MOSFET?

Answer 39

The MOSFET has a higher input impedance.

Question 40

What are the four elements of the MOSFET?

Answer 40

Gate, source, drain, and substrate.

Question 41

The substrate of an N-channel MOSFET is made of what material?

Answer 41

P-type material.

Question 42

In a MOSFET, which element is insulated from the channel material?

Answer 42

The gate terminal.