Module 1: Components

Question 1

What are the four types of resistors?

Answer 1

• carbon composition
• carbon film
• metal film
• wire-wound

Question 2

Explain the constructional features of a carbon composition resistor, as well as some advantages and disadvantages.

Answer 2

• made of a mixture of finely ground carbon (conductor) and an insulating mixture (insulator)
• the ratio of carbon : insulator gives resistance values
• good for short but large overloads (lots of bulky resistive material)
• bad frequency response (noisy over 10MHz due to capacitive/inductive properties)

Question 3

Explain the constructional features of a carbon film resistor, as well as some advantages and disadvantages.

Answer 3

• the general resistors one would use for breadboards
• a helical track through the resistive material (thus exposing the conductive carbon) creates the resistance (changing pitch of helix changes the resistance)
• good: very close tolerances
• bad: resistance drifts with temperature

Question 4

Explain the constructional features of metal film resistors, as well as some advantages and disadvantages.

Answer 4

• similar to carbon film except for the resistive material used
• good: don’t drift as much with temperature; good for high-freq. applications; less expensive

Question 5

What are wire-wound resistors, and why are they used?

Answer 5

Literally some wire wound around an insulating object. They dissipate more heat and are thus used in high-power applications.

Question 6

What type of capacitor has the best frequency range/response?

Answer 6

Ceramic capacitors (work at anything below 100MHz)

Question 7

What type of capacitor has the highest capacitance, and what are some of its features?

Answer 7

Tantalum (electrolytic)

Tantalum metal foil with solid semi-conductor in between

Up to 2mF capacitance!!

Question 9

How can supercapacitors store so much charge? Draw a diagram showing where positive and negative ions are.

Answer 9

• plates are soaked in charcoal, making them able to attract and absorb more electroncs (effectively a larger surface area, which increases capacitance)
• because of a thin dialetric between the two plates, the distance affecting capacitane is far smaller

Question 10

Why is there a need for balancing networks when charging supercapacitors, and what might this look like?

Answer 10

Supercapacitors vary signficantly in their internal capacitance - it is quite common to find one cell with a capacitance of 100F, and another with 130F! If connected in series across a voltage source, they would both charge to different amounts.

To prevent this, one must use an appropriately size resistor network to ensure the current supplied is the same.

Question 11

How do variable capacitors work?

Answer 11

Moving plates over each other - when they are fully over each other it is the maximum capacitance.

Question 12

What is a unijunction transistor?

Answer 12

A p-n junction with three pins, used in timing circuits.

Question 13

What is a zener diode, and how is it used?

Answer 13

A diode used in reverse-biased position that conducts in one direction but doesn’t in the other. Its claim to fame, however, is that when reverse biased, it blocks anything below a certain volage (Zener voltage), and allows anything exceeding that.

Question 14

What is a varactor diode?

Answer 14

A diode that acts as a capacitor when reverse biased.

Question 15

What is a Siliconm Controlled Rectifier, or Thyristor?

Answer 15

A device that may be switched from a non-conductive state to a conductive one when applying current to the gate. Instead of amplifying it (like a transistor), it simply makes the cathoe - anode conductive.

Question 16

What is a Triac?

Answer 16

Conducts current in both direction and is triggered in to conduction by a negative or positive pulse.

Question 17

What impact may low temperatures have on electronic components?

Answer 17

• any electrolyte (capacitor, batteries, etc…) may freeze and fail
• some silicon and germanium-doped materials don’t function well, as they depend on thermal excitation for charge carriers to exist
• any water vapour or condensation build up may cause cracking when it turns to ice

Question 18

What impact may high temperatures have on electronic devices?

Answer 18

• the increased thermal load may exceed the limits of any heat sink and cause failure
• very fast thermal overload can ruin solder joints

Question 19

What is a known thermal weak point in electronic devices, and what are some ways to mitigate this?

Answer 19

Solder joints

Use gold wires and special solder alloys (e.g. Gold-Tin)

Question 20

What are ‘tin whiskers’, and how can they affect electronic circuits?

Answer 20

Metal whisker formations from solder.

They can bridge across terminal strips, connectors, or PCB tracks, thus ruining components.

Question 21

What are ‘thermal joint compounds’, and how may they be used?

Answer 21

Special heat conductive pastes used between mating surfaces - e.g. heatsink and GPU.

Question 22

What is an ‘isolating kit’, and why are they useful?

Answer 22

Often, the voltage out pin of an IC is connected to the actual frame of the IC. This means the frame is live! To prevent this, one may purchase an ‘isolating kit’, which is a thin piece of dialetric (mica) to be placed between the IC and the heatsink.

Question 23

What is this connector, and what is it used for?

Answer 23

It’s a PS/2 connector, developed by IBM to connect mice and keyboard to a computer.

Question 24

What are the two types of communucation ‘ports’, or protocols?

Answer 24

Serial and parallel

Question 25

Why wouldn’t you use a VGA port + connector in a modern home theatre set-up?

Answer 25

They are reduced quality and traditionally can only carry analogue signals up to 648x480.

Question 26

What’s a display port?

Answer 26

a digital interface supporting multiple channel audio and video at very high resolutions.

Question 27

Label the below USB 2.0 pins

Answer 27

4 = Vcc, 3 & 2 = data, 1 = GND