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                                                                  electricity in nature

a bright manifestation of electricity in nature serve as lightning, electrical nature of which was established in the 18th century. lightning has long caused forest fires. according to one version it was lightning led to the original synthesis of amino acids and the emergence of life on earth .

all processes in the nervous system of humans and animals is crucial dependence of the capacity of the cell membrane for sodium ions from the potential of the intracellular environment. after increase the voltage on the cell membrane sodium channel opens at the time of the order of 0.1 - 1.0 ms., that leads to an explosive growth of tension, then the difference of potentials on the diaphragm returns to its original value. the process described briefly called the nerve impulse. in the nervous system of animal and human information from one cell to another transmit nerve impulses duration of about 1 ms. the nerve fiber is a cylinder filled with electrolyte. excitation signal is transmitted without a decrease in amplitude due to the effect of a short-term increase membrane permeability to sodium ions.many fish use electricity for protecting and searching production under the water. discharge voltage of the south american electric eel can reach a value of voltage of 500 volts. the power of the discharge of the electric ray can reach 0.5 kw. sharks, lamprey, some сомообразные use electricity to search for prey. electric body of the fish works with a frequency of several hundred hertz and creates tension in a few volts. the electric field is captured electricreceptors. located in the water objects distort the electric field. for these distortions fish easily oriented in muddy water. therefore, electricity plays a big role in nature.

Длина = х ширина = у составляем систему уравнений:   {х + 1/4у = 7                            {х + у = 10    → x = 10 - y  → подставляем значение х в 1-ое уравнение                                               получаем:                                                 10 - у + 1/4у = 7                                                 10 - 3/4у = 7                                                 3/4у = 10 - 7                                                 3/4у = 3                                                     у = 4 х = 10 - у х = 10 - 4 х = 6 ответ: х = 6;   у = 4

Составляем пропорцию решения:   х-100%                                                                 900-12%                                       х/900=100/12(перемножаем крест на крест)                                       12х=90000                                           х=7500