Answer:
The focal length of a lens is refers to the distance from the center of the lens to the principal foci.
Answer:
The two poles of the bar magnet change positions. The compass needle spins a half circle.
Explanation:
If you know an element’s atomic number, you will learn the number of protons and electrons. The atomic number is equal to the number or protons and electrons. You can also find the number of neutrons, by subtracting the atomic mass from the atomic number.
For example, Fluorine’s atomic number is 9, and its atomic mass is 19. So, the number of electrons and protons in fluorine is 9. The number of neutrons the is equal to 19-9. Thus, Fluorine has 10 neutrons.
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