Avionics Multiple Choice Questions on “Electromagnetic Spectrum”.
1. Cps is the unit of what?
a) Frequency
b) Amplitude
c) Phase
d) Gain
Answer: a
Clarification: Cps or cycles per second is an alternative unit for the frequency of an EM wave. The other unit for frequency is Hertz which is more commonly used around the world.
2. The range of electromagnetic signals encompassing all frequencies is referred to as?
a) EM waves
b) EM frequency
c) EM spectrum
d) EM radiation
Answer: c
Clarification: The range of electromagnetic signals encompassing all frequencies is referred to as Electromagnetic spectrum. It includes radio waves, microwaves, optical waves, x-rays, gamma rays and cosmic waves.
3. The distance that the wave travels in one cycle is called as?
a) Displacement
b) Wavelength
c) Cycle length
d) Cycle amplitude
Answer: b
Clarification: The wavelength of a wave is the distance the wave travels in one cycle. The wavelength of a signal is represented by the Greek letter λ (lambda) and has the same units as length.
4. What is the wavelength of a signal with a frequency of 150Mhz?
a) 10m
b) 2m
c) 5m
d) 20m
5. What is the frequency of the EM wave with a wavelength of 12cm?
a) 2.4Ghz
b) 2.5Ghz
c) 250 Mhz
d) 0.25Mhz
6. A signal travels a distance of 75 ft in the time it takes to complete 1 cycle. What is its frequency?
1 m 5 3.28 ft
a) 13Mhz
b) 13.12Mhz
c) 14Mhz
d) Cannot be determined
Answer: b
Clarification: 1m=3.28ft
75/3.28=22.86m
Frequency= 300/22.86 =13.12Mhz.
7. The maximum peaks of an electromagnetic wave are separated by a distance of 8 in. What is the frequency?
a) 256.4Khz
b) 1477.8Khz
c) 1477.8Mhz
d) 256.7Mhz
Answer: c
Clarification: Wavelength =8 in.= 0.203 m
Frequency = 300/0.203 = 1477.8Mhz.
8. SHF Em waves are used in?
a) Ground to ground communication
b) Satellite communication
c) Aircraft to ATC communication
d) Underwater communication
Answer: b
Clarification: SHFs or Super High Frequency EM waves are those which lie between the frequency range of 3 to 30GHz range. These microwaves frequencies are widely used in satellite communication and radar.
9. Which one of the following is not a source of infrared radiation?
a) Human bodies
b) Light bulbs
c) Sun
d) Books
Answer: d
Clarification: Infrared radiation is generally associated with heat. Infrared is produced by light bulbs, human bodies, and basically any physical equipment that generates heat.
10. Which one of the following is not a reason for not using X-rays in communication?
a) Highly attenuated
b) High power is required
c) Stopped by ionizing effects
d) Ionizing radiation
Answer: c
Clarification: X-rays are not stopped by ionizing effects and that was the only reason they were ever thought they could be used in communication. In re-entry vehicles, a temporary communication cut off is experienced due to ionizing effects. X- rays were hard to modulate and focus and hence gradually let down.
11. The portion of the electromagnetic spectrum occupied by a signal is called ________
a) Signal spectrum
b) Bandwidth
c) Frequency width
d) Signal strength
Answer: b
Clarification: Bandwidth is that portion of the electromagnetic spectrum occupied by a signal. It is also the frequency range over which a receiver or other electronic circuit operates. More specifically, bandwidth is the difference between the upper and lower frequency limits of the signal or the equipment operation range.
12. What is the bandwidth of a signal having 928Mhz and 902Mhz as its upper and lower frequencies?
a) 26Mhz
b) 26Hz
c) 1830Hz
d) 1830Mhz
Answer: a
Clarification: Bandwidth = upper frequency – lower frequency = 928Mhz – 902Mhz =26Mhz.
13. What is the upper frequency of a signal with a bandwidth of 6Mhz, if the lower frequency limit is 54Mhz?
a) 60Mhz
b) 48Mhz
c) 60Hz
d) 48Hz
Answer: a
Clarification: Bandwidth = upper frequency – lower frequency
Upper frequency = bandwidth + lower frequency = 54Mhz + 6Mhz = 60Mhz.
14. Higher frequencies can have more channels for a particular bandwidth.
a) True
b) False
Answer: a
Clarification: The benefit of using the higher frequencies for communication carriers is that a signal of a given bandwidth represents a smaller percentage of the spectrum at the higher frequencies than at the lower frequencies. It means that there can be more number of channels with the same bandwidth in higher frequency than lower frequencies.
15. Which organization regulates international EM spectrum division?
a) ITU
b) FCC
c) NTIA
d) WCC
Answer: a
Clarification: The International Telecommunications Union (ITU), an agency of the United Nations that is headquartered in Geneva, Switzerland, comprises 189 member countries that meet at regular intervals to promote cooperation and negotiate national interests. The ITU brings together the various countries
to discuss how the frequency spectrum is to be divided up and shared. Because many of the signals generated in the spectrum do not carry for long distances, countries can use these frequencies simultaneously without interference.