Both systems have benefits and disadvantages.
Benefits of the Metric System
<span>Easier for anything involving conversions.Celsius is based on the the freezing and boiling points of water.Is the most popular system of measurement worldwide. This gives interchangeability internationally.Other systems of measurement, like U.S. standard units, are tied directly to metric units so they can be converted back and forth.<span>You can sell to the government since governments (including the U.S. government) require government contractors to use the metric system for most things.</span></span>
As per the question the wavelength of spectral line of the neutral hydrogen atom is 21 cm.
Spectral line of hydrogen atom will be observed when an electron will jump from higher excited to the ground state. If E is the energy of the ground state and E' is the energy of the higher excited state,the energy emitted when electron will jump from higher excited to ground state is E'-E.
As per Planck's quantum theory -

Where f is the frequency of emitted radiation and h is the Planck's constant.Actually this energy emitted is also electromagnetic in nature. We know that all the electromagnetic radiation will move with the same velocity which is equal to the velocity of light.
The velocity of light c= 3×10^8 m/s.Hence the velocity of wave corresponding to this spectral line is 3×10^8 m/s.
We know that velocity of a wave is the product of frequency and wavelength of that corresponding wave. Mathematically we can write it as-

[
is the wavelength of the wave ]
It is given that wavelength =21 cm=0.21 m
The frequency is calculated as -




Hence the antenna will be tuned to a frequency of 14.2857×10^8 Hz
Here Hertz[ Hz] is the unit of frequency.
The correct answer is B. barometer
Thermometer is used to measure temperature, anemometer is used to measure wind speed, while a hygrometer is used to measure humidity.
Answer:
B
Explanation:
there moving the waves through energy
Answer:
Predicting the size, location, and timing of natural hazards is virtually impossible, but now, earth scientists are able to forecast hurricanes, floods, earthquakes, volcanic eruptions, wildfires, and landslides using fractals.
Explanation: