### Exercise 1

Question 16 :

What frequency range is the High Frequency band?

A). 100 kHz
B). 1 GHz
C). 30 to 300 MHz
D). 3 to 30 MHz
Answer : Option D

Explanation :

The HF band is based on frequencies 3 to 30 Mhz. AM radio stations are in the HF band but normally are stated in kilohertz.

Question 17 :

The first step to getting output from a laser is to excite an active medium. What is this process called?

A). Pumping
B). Exciting
C). Priming
D). Raising
Answer : Option A

Explanation :

A collection of atoms or molecules that can be excited to a higher energy state is called an active medium. Before lasing can occur, the active media is "pumped". The process of raising the atoms in the active media from a lower energy state to a higher state is like pumping water up from a well.

Question 18 :

What is the relationship between resistivity r and conductivity s?

A). R = s2
B). R = s
C). R > s
D). R = 1/s
Answer : Option D

Question 19 :

Which motor is NOT suitable for use as a DC machine?

A). Permanent magnet motor
B). Series motor
C). Squirrel cage motor
D). Synchronous motor
Answer : Option C

Explanation :

The squirrel cage motor is the only one without any connection to the armature.

Question 20 :

A given signal's second harmonic is twice the given signal's __________ frequency...?

A). Fourier
B). Foundation
C). Fundamental
D). Field
Answer : Option C

Explanation :

A given signal's second harmonic is twice the given signal's fundamental frequency. Harmonics are generated when there are non-linearities in an amplifier (there are always non-linearities). The worse the non-linearities, the more harmonics. A signal at 27.5 MHz (approximate frequency for US citizen's band) would have a second harmonic at 55.0 MHz (on US channel 2!). Can you see why there might be problems? A CB operator might do well to place a low-pass filter on his radio.