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? 發問於 科學及數學其他 - 科學 · 1 十年前

physics problems

1. An electric bell connected to a battery is sealed inside a large jar. what happeds as the air is removed from the jar?

(1) the electric circuit stops working because electromagnetic radiation can not travel through vacuum.

(2) the pitch of the bell decreases because the frequency of the sound waves is lower in a vacuum than in air.


(3) the loudness of the bell increases because of decreased air resistance.

(4) the loudness of the bell decreases because sound waves can not travel through a vacuum

please explain in details

1 個解答

  • 1 十年前

    The answer is (4). The loudness of the bell decreases because sound waves cannot travel through a vacuum.

    For (3) and (4), sound waves require a medium for propagation. That is, sound waves need vibration of particles for travelling. However, in vaccum, there is no particles, so sound waves cannot travel. For (3), it is definitely wrong, because increase in air resistance will help the propagation of sound waves. (More number of air particles).

    For (1), EM waves can travel through vacuum, so the electric circuit will continue to work.

    For (2), The frequency of waves depends on the source of the emission. That is, the bell in this case. When waves travel from one medium to another, the frequency will never change. So, this statement is wrong.

    資料來源: Myself~~~