Hi,

Resistance is the property of a material by virtue of which it opposes the flow of electrons through the material. It restricts the flow of the electron through the material. It is denoted by (R) and is measured in ohms (Ω). When the voltage is applied across the resistor the free electrons start accelerating .

You have to understand the process of charge flow in a material, a material has electrons in outermost layers, which are bound to molecules or atoms in different ways— some are free to move, to lesser degree in some materials than in others.

Electrons in this layer are constantly in random movement, jumping from atom to atom, or molecule to molecule. The process is absolutely random , with there being no net movement of electrons in any direction.

Under the effect of external electric potential difference between two points in material, a field comes to exist in one direction. The random electron movement now is also seeing this external field, and gets affected by it, resulting in a net drift of electrons towards the positive side (higher potential side).

Thus the random movement generates a net drift of charges, which makes for the current. By simple logic, more the potential difference, stronger is the field, and hence larger the net drift of charges- means more current.

Now the resistance part. Electrons in different materials have different degree of freedom, and electron random movement also is lower or higher accordingly. Therefore the drift under electric field is also lesser or more accordingly. So for the same potential difference, current in two materials will be different .

This property of different degree of freedom of electrons, resulting in different currents in different materials for the same potential difference, is what is expressed by the terms “resistivity “ or “conductivity “, the two terms carrying opposite meaning- one denotes the resistance faced by current, while the othet denotes ease of charge flow.

Materials which conduct charge relatively easily also differ in degree of ease, and those that offer higher resistance go to form resistors.

Materials which heavily oppose the charge flow due to extremely low number of electrons free to jump, make for the class of insulators.

Hope this helps.