If the scientist repeats the experiment over and over and gets the same results. Also if the scientist peer reviews the experiment to make sure there is no bias in his or her results.
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Answer:
Space technology is technology developed by space science for use in astronautics, for purposes such as spaceflight or space exploration. Space technology includes spacecraft, satellites, space stations, and support infrastructure equipment, and procedures and space warfare.
For a cylinder that has both ends open resonant frequency is given by the following formula:

Where n is the resonance node, v is the speed of sound in air and L is the length of a cylinder.
The fundamental frequency is simply the lowest resonant frequency.
We find it by plugging in n=1:

To find what harmonic has to be excited so that it resonates at f>20Hz we simply plug in f=20 Hz and find our n:

We can see that any resonant frequency is simply a multiple of a base frequency.
Let us find which harmonic resonates with the frequency 20 Hz:

Since n has to be an integer, final answer would be 323.
Answer:
There are many types of magnets, which are generally divided into two categories: permanent magnet and a soft magnet.
Explanation: