1. What is the speed of radio waves in vacuum?
A.
3.0 × 10^6 m/s
B.
3.0 × 10^8 m/s
C.
3.0 × 10^10 m/s
D.
3.0 × 10^12 m/s
Correct Answer:
3.0 × 10^8 m/s
Explanation:
Radio waves are electromagnetic waves, and all electromagnetic waves travel in vacuum at approximately 3.0 × 10^8 m/s.
2. Radio waves travel in air at a speed that is approximately equal to:
A.
3.0 × 10^8 m/s
B.
3.0 × 10^5 m/s
C.
3.0 × 10^3 m/s
D.
3.0 × 10^10 m/s
Correct Answer:
3.0 × 10^8 m/s
Explanation:
Air is very close to vacuum in its effect on radio-wave speed, so radio waves travel through air at approximately 3.0 × 10^8 m/s.
3. Which expression gives the speed of a radio wave in vacuum?
A.
v = fλ
B.
v = λ/f
C.
v = f/λ
D.
v = 1/(fλ)
Correct Answer:
v = fλ
Explanation:
The speed of any wave, including a radio wave, is given by the product of its frequency and wavelength: v = fλ.
4. A radio wave has a frequency of 100 MHz in vacuum. What is its wavelength? Take the speed of light as 3.0 × 10^8 m/s.
A.
0.3 m
B.
3 m
C.
30 m
D.
300 m
Correct Answer:
3 m
Explanation:
Using λ = v/f, λ = (3.0 × 10^8)/(100 × 10^6) = 3 m.
5. A radio wave has a wavelength of 6 m in vacuum. What is its frequency? Take the speed of light as 3.0 × 10^8 m/s.
A.
5 MHz
B.
50 MHz
C.
500 MHz
D.
5 GHz
Correct Answer:
50 MHz
Explanation:
Using f = v/λ, f = (3.0 × 10^8)/6 = 5.0 × 10^7 Hz, which is 50 MHz.
6. If the frequency of a radio wave in vacuum is doubled, what happens to its speed?
A.
It becomes half
B.
It becomes double
C.
It remains 3.0 × 10^8 m/s
D.
It becomes zero
Correct Answer:
It remains 3.0 × 10^8 m/s
Explanation:
The speed of a radio wave in vacuum is constant at approximately 3.0 × 10^8 m/s, regardless of its frequency.
7. Which radio wave travels faster in vacuum?
A.
A wave with frequency 1 MHz
B.
A wave with frequency 10 MHz
C.
A wave with frequency 100 MHz
D.
All travel at the same speed
Correct Answer:
All travel at the same speed
Explanation:
All radio waves, regardless of frequency, travel at the same speed in vacuum: approximately 3.0 × 10^8 m/s.
8. A radio signal travels for 2 seconds through vacuum. Approximately how far does it travel?
A.
1.5 × 10^8 m
B.
3.0 × 10^8 m
C.
6.0 × 10^8 m
D.
9.0 × 10^8 m
Correct Answer:
6.0 × 10^8 m
Explanation:
Distance is speed multiplied by time: d = (3.0 × 10^8)(2) = 6.0 × 10^8 m.
9. A radio wave travels 900 km in air. Approximately how long does it take? Take its speed as 3.0 × 10^8 m/s.
A.
0.003 s
B.
0.03 s
C.
0.3 s
D.
3 s
Correct Answer:
0.003 s
Explanation:
Convert 900 km to 9.0 × 10^5 m. Then t = d/v = (9.0 × 10^5)/(3.0 × 10^8) = 3.0 × 10^-3 s.
10. Compared with its speed in vacuum, the speed of a radio wave in a material medium is generally:
A.
Always greater
B.
Usually lower
C.
Always zero
D.
Exactly the same in every medium
Correct Answer:
Usually lower
Explanation:
Radio waves generally travel more slowly in a material medium than in vacuum, where their speed is approximately 3.0 × 10^8 m/s.
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