Question 16 :
What frequency range is the High Frequency band?
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 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?
Question 19 :
Which motor is NOT suitable for use as a DC machine?
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 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.