Question

17. What is resistance?

Answer 1

✔✔✔✔Resistance is the property of any material to↪ resist or oppose the flow of current↩ ✔✔✔✔

Answer 2

What is resistance?

Resistance in a conductor can be defined as the opposition offered to the flow of electrons. For a conductor of uniform cross-sectional area resistance is directly proportional to the length of the conductor and inversely proportional to the cross-sectional area of the conductor.

Therefore, R∝L/A.

Or,R=ρL/A ,where ρ is called resistivity of the conductor.

SI Unit of resistance is Ohm(Ω).

For a wide range of materials and conditions, voltage across the conductor and the current flowing through it are directly proportional to each other,

Or, V∝I

Or, V=RI( This known as Ohm’s law)

Or, R=V/I

Therefore,resistance is constant for materials obeying Ohm’s law,this type of materials are called Ohmic materials. For active elements voltage and current are not proportional to each other,therefore resistance is constant. In such cases, resistance is calculated from graph of V vs I, therefore r=dv/dt.

Inverse of the resistance is called conductance.

Or, G=1/R, SI unit of conductance is mho or Siemens.