CLASS 10TH PHYSICS NOTES [ELECTRICITY]

 

ELECTRICITY

 

 

·     Electricity has an important place in modern society. It is a controllable and convenient form of energy for a variety of uses in homes, schools, hospitals, etc.

 

ELECTRIC CURRENT AND CIRCUIT

·     We are familiar with air current and water current. We know that flowing water constitutes water current in rivers. Similarly, if the electric charge flow through conductor [through metallic wire], we say that there is electric current in conductor. In torch, we know that the cells [or a battery, when placed in proper order] provide flow of charge of electric current through the bulb to glow. We have seen that the torch gives light only when switch is on. A switch is a conducting link between the cell and the bulb. A continuous and closed path of electric current is called electric circuit. Now, if the circuit is broken anywhere [or switch is turned off], the current stop flowing and bulb does not glow.

·     Electric current is expressed by the amount of charge flowing through a particular area in unit time. In other words, it is a rate of flow of charges. However, electrons were not known at the time when phenomena of electricity was first observed. So, electricity current was a considered to be the flow of positive charges and direction of flow of positive charges was taken to be the direction of electric current is taken as opposite to the direction of the flow of electrons, which are negative charges.

·     If a net charge Q, flows across any cross-section of conductor in time t, then the current I, through the cross-section is

                                                                                              

                                                                                I = Q / T

Ø I= electric current.

Ø Q= charge.

Ø T= time.

·     Then the SI unit of electric charge is coulomb[C], which is equivalent to the charge contained is nearly 6 x 10^18electrons.[we know that an electron possesses a negative charge of 1.6 x 10^-19C] The electric current is expressed by a unit called ampere[A], named after the French scientist, Andre-Marie Ampere (1775-1836). One ampere is constituted by the flow of one coulomb of charge per second, that is, 1A= 1C/1s. small quantities of current are expressed in milliampere [1 ma = 10^-3 A] and microampere [1microampere = 10^-6 A].