The restrictions imposed by China on rare earth metals has resulted in some companies (e. g., Toyota, Renault, Tesla) starting to look for alternatives. They plan to use parts that do not include rare earth metals. Is this a good solution?

Short term Yes,

Explanation: Japan recently stumbled upon a pile of rare metals and North Korea is currently sitting on the world’s largest wealth of rare minerals. As soon as North Korea denuclearized, sanctions will be lifted and foreign companies will rush in to grab a piece. Therefore in the long term, they can always source it from elsewhere.

Assuming China keeps the restriction on for the long term, then it would lose its competitiveness when newer players come in.

Yes

Explanation:

The most important way to ensure the existence of the human race is to ensure that our natural resources are not depleted such that we will pose environmental problem to our space, hence the restriction imposed by China on rare earth metals is a step in the right direction.

In addition to the above, these are resources that are non-renewable and in few decades to come, we might not be able to access these resources again, thus a need to ensure their availability for future use.

It can be concluded that this restriction will give room to look into another means of creating wealth as well as employment as we may have to invest into ideas that will generate an alternative to these resources.

This will also protect the environment as earlier mentioned.    

sound is invisible, but sometimes we can feel it. when a kettle-drum is thumped with a stick that time the tight drum skin moving up and down very quickly for some time and then it pumped sound waves into the air. loudspeakers also work in a similar manner.

components of a speaker:

electromagnet

in order to translate an electrical signal into an audible sound, an electromagnet is used in looudspeakers

  suspension

suspension is used to   center the voice coil in the gap of the magnet and it exerts a restoring force to keep it there. suspension is used to limits the maximum mechanical excursion of the diaphragm and voice coil.

voice coil

voice coil is a coil of wire which is attached to the apex of a loudspeaker cone. it provides the motive force to the cone by the reaction of a magnetic field to the current passing through it.

cone

in a   loudspeaker, a   thin, semi-rigid membrane attached to the voice coil, which moves in a magnetic gap due to which it vibrates   and produced sound. it is known as diaphragm and it can also be called a cone, though not all speaker diaphragms are cone-shaped.

surround

surround is also known as front suspension. surround is used to join the cone to the chassis. together with the suspension it controls the cone excursion, and it is also used to   determine how energy which is   travelling through the cone is absorbed, and how the speaker limits when it reaches the ends of its travel.

dustcap

dustcap is used to protect the voice coil from dust and dirt. it is a part of the cone.

how speaker work

the outer part of the cone is fastened to the outer part of the loudspeaker's circular metal rim. the inner part is fixed to   voice coil that sits just in front of a permanent magnet . when loudspeaker is hooked up to a stereo, electrical signals feed through the speaker cables into the coil. it will convert the coil into an electromagnet magnet . when electricity flows back and forth in the cables, the electromagnet either repels or attract the permanent magnet. this moves the coil back and forth, and it pull and push the loudspeaker cone. like a drum skin vibrating back and forth, the moving cone pumps sounds out into the air.in this way loudspeakers works.

2,283,000

explanation:

i just had to add it