AY Honors/Radio Electronics/Answer Key

Radio Electronics

Identify the value of resistors by the color code

The value of a resistor is marked on the device itself by using bands of colors. The color code assigns a number to each of the following colors:

• 0 - black
• 1 - brown
• 2 - red
• 3 - orange
• 4 - yellow
• 5 - green
• 6 - blue
• 7 - violet
• 8 - grey
• 9 - white

Note that after black and brown, the next six colors are arranged as they are found in the rainbow. These colors can also be memorized by the use of a mnemonic such as "Black Bears Run Over Yellow Grass, But Vultures Glide over Water."

Two other colors are used to specify the tolerance of the resistor - that is, how close the actual value is to the value encoded on it:

• 5% - gold
• 10% - silver

If there is no gold or silver band, the resistor has a 20% tolerance.

Remember that just as "gold is better than silver," a 5% (gold) resistor is better than a 10% (silver) resistor.

On a four-band resistor, the third band represents the number of zeros that follow the first two digits, and the fourth band represents the tolerance. So a brown-black-red-gold combination would indicate a 1000 Ohm resistor with a 5% tolerance.

Resistors with tighter tolerance are usually specified with three bands indicating the numeric value and a fourth indicating the number of zeroes following.

Know and understand Ohm's Law.

If a voltage is applied across a resistor, current will flow through it. Ohm's law describes the relationship between this current, voltage, and resistance. It can be written as

[math]\displaystyle{ v = i r }[/math]

Where v is volatage (measured in volts), i is current (measured in amps), and r is resistance (measured in ohms). The equation can also be written as

[math]\displaystyle{ i = \frac{v}{r} }[/math]

and

[math]\displaystyle{ r = \frac{v}{i} }[/math]

Basically, it means that if the voltage is held constant and the resistance is decreased, the current is increased. Or if the resistance is held constant and the current is increased, the voltage will also increase.

What is meant by a parallel and a series circuit?

A series circuit is a circuit in which the components are placed end-to-end. The circuit below shows two resistors in series:

o---/\/\/\-----/\/\/\----o

In a series circuit the current flowing through both devices will be equal, but the voltage across them will be different if the resistances are different.

A parallel circuit connects both terminals of two components together. The circuit below shows two resistors in parallel:

     +----/\/\/\----+
o----+              +------o
     +----/\/\/\----+

In a parallel circuit, the voltage across the two resistors will be identical, but the current divides between them. Some current goes through the top, the rest goes through the bottom.

List ten ways electronics are used in everyday life.

1. Computers - for work and for play.
2. Entertainment - Televisions, stereos, video games, toys, etc.
3. Medical - Patient monitoring
4. Industrial - motor controllers, robotics, etc.
5. Appliances - microwaves, timers, ovens, refrigerators, washing machines, dryers.
6. Radio Communications - police and fire radios, CB radios, fleet radios.
7. Telecommunications - telephones, fax machines.
8. Fire Safety - fire alarms, smoke detectors, sprinkler systems.
9. Water Supply - water towers signal pumping stations, etc.
10. Security - metal detectors and x-ray machines at airports, anti-theft devices in stores, security camera.
11. Music - amplifiers, synthesizers, sound mixers, recording equipment.