Question

Draw a graph between resistance R and cross section A area of a conducting material having wires of different arc of cross section

Answer 1

While a voltage is applied across any substance, electric currentstarts flowing through it. But if we observe carefully, the electric currentflows through the all substances are not equal even when the same voltage is applied across each of the substances. This is because currentcarrying capacity of all substances is not equal. The electric currentdepends upon the number of electrons' crosses the cross-section per unit time. Again this number of electrons crossing the cross-section is dependable on the free electrons available in the substances. If free electrons are plenty in a substance, the amount of current is more for same applied voltage across the substances. The electric currentthrough a substance not only depends upon the number of free electrons in it, but also depends upon the length of path an electron has to travel to reach from lower potential end to higher potential end of the substance. In addition to that, every electron has to collide randomly with other atoms and electrons in numbers of times during its traveling.
So, every substance has a property to resist current through it and this property is known as electric resistance.