(a) State Ohm's law.
(b) Define resistance. Give its SI unit.

How will you establish the electrons carry current?

Establish the relation between current and drift velocity.

Define the term resistivity and write its S.I. unit. Derive the expression for the resistivity in terms of number density of free electrons and relaxation time.

Ramaniamma was a childless window. She ran her life only by the pension for the Sr. citizens from the Government. When she switches ON one bulb in her house, all the other appliances get switched OFF. She could not even spend for an electrician. Sujatha living nearby decided to do something for her. She referred to Physics books and learned that the series combination for the household connection could be the reason. She called an electrician and had the circuit changed to parallel combination. The problem was solved and Ramaniamma was happy. She thanked Sujatha for her help to solve the problem.
Read the above passage and answer the following questions.
(i) What are the values possessed by Sujatha?
(ii) Why a parallel combination is used for household? Give two advantages.

Current flowing through a wire varies with time t in second as I = (2t + 4) A. How much charge passes through a cross section of the wire in 2 sec?

You are given a 8 \(\Omega\) resistor. What length of constant wire of resistance 120\(\Omega\) m^-1 should be joined in parallel with it to get a value of 6\(\Omega\)?

A silver wire has a resistance of 2.1\(\Omega\) at 27.5^oC and a resistance of 2.7\(\Omega\) at 100^oC. Determine the temperature coefficient of resistivity of silver.

A storage battery of emf 8.0 V and internal resistance 0.5 \(\Omega\) is being charged by a 120V dc supply using a series resistor of 15.5 \(\Omega\). What is the terminal voltage of the battery during charging? What is the purpose of having a series resistor in the charging circuit?