Liberia, a very poor nation in West Africa, is relatively abundant in resources such as mahogany and rubber tree forests, iron-ore deposits, and diamonds. If Liberia is so rich in valuable resources, why is it still so impoverished? a) Liberia lacks the institutions necessary to make productive use of those resources. b) The population of Liberia is too small to use those resources. c) Natural resources are not as important as other types of resources. d) Taxes in Liberia are too high and discourage investment. e) Liberians are content with a low standard of living.

A. Liberia lacks the institutions necessary to make productive use of those resources.

Explanation: Liberia is a nation rich with natural resources including iron ore, gold, diamonds, natural rubber, vast forest for logging and timber harvesting, and vast agriculture land for ensuring food security.

Liberia is Africa's oldest republic, but it became known in the 1990s for its long-running, ruinous civil war and its role in a rebellion in neighboring Sierra Leone. Around 250,000 people were killed in Liberia's civil war, and many thousands more fled the fighting.

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.