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Electrical Resistance


Electrical resistance of a cylindrical wire of length $l$ and cross-sectional area $A$ is \begin{align} R=\rho\frac{l}{A} \end{align} where $\rho$ is the resistivity of the wire's material. The unit of resitance is ohms ($\Omega$).


The resistance of conductors usually increase with temperature as \begin{align} R_T=R_0\left(1+\alpha (T-T_0)\right) \end{align} where $R_0$ is resistance at temperature $T_0$, $R_T$ is the resistance at tempertaure $T$ and $\alpha$ is the thermal coefficient of resistance.

Problems from IIT JEE

Problem (JEE Mains 2022): A 1 m long wire is broken into two unequal parts A and B. The A part of the wire is stretched into another wire C. Length of C is twice the length of A and the resistance of C is twice that of B. Find the ratio of length of A and B.

  1. $1:4$
  2. $1:2$
  3. $4:1$
  4. $2:1$

Problem (JEE Mains 2021) The resistance of a conductor at 15 deg C is 16 ohm and at 100 deg C is 20 ohm. What will be the temperature coefficient of resistance of the conductor?

  1. 0.003 /deg C
  2. 0.010 /deg C
  3. 0.033 /deg C
  4. 0.042 /deg C


  1. Colour code for resistors
  2. Series and Parallel Arrangements of Resistances
  3. Wheatstone bridge
  4. Symmetry in electrical circuits
  5. Resistance of an Electric Bulb
  6. Specific resistance of the material of a wire using meter bridge and post office box
  7. Ohm's Law
  8. Resistance (Expt)
JEE Physics Solved Problems in Mechanics