NCERT Solutions for Chapter: Current Electricity, Exercise 1: MCQ

Consider a current-carrying wire (current $I$) in the shape of a circle. Note that as the current progresses along the wire, the direction of $J$ (current density) changes in an exact manner, while the current $I$ remains unaffected. The agent that is essentially responsible for this is:
 

Two batteries of emf ${\epsilon }_1$, and ${\epsilon }_2\left({\epsilon }_2>{\epsilon }_1\right)$and internal resistances $r_1$ and $r_2$ respectively are connected in parallel as shown in figure

A resistance $R$ is to be measured using a meter bridge. Student chooses the standard resistance $S$ to be $100\mathrm{\Omega }$. He finds the null point at $l_1=2.9 \mathrm{cm}$. He is told to attempt to improve the accuracy. Which of the following is a useful way?

Two cells of emf approximately $5\mathrm{V}$ and $10\mathrm{V}$ are to be accurately compared using a potentiometer of length $400\mathrm{cm}$.

A metal rod of length $10 \mathrm{cm}$ and a rectangular cross-section of $1 \mathrm{cm}\times \frac{1}{2} \mathrm{cm}$ is connected to a battery across opposite faces. The resistance will be
 

Which of the following characteristics of electrons determines the current in a conductor?