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

Consider a simple circuit shown in Figure     stands for a variable resistance $R\text{'}$. $R\text{'}$ can vary from $R_0$ to infinity, $r$ is internal resistance of the battery.

Which of the following is TRUE ?

The measurement of an unknown resistance $R$ is to be carried out using Wheatstone bridge . Two students perform an experiment in two ways. The first students takes ${\mathrm{R}}_2=10\mathrm{\Omega }$ and $R_1=5\mathrm{\Omega }$ The other student takes $R_2=1000\mathrm{\Omega }$ and $R_1=500\mathrm{\Omega }$. In the standard arm, both take $R_3=5\mathrm{\Omega }$. Both find $R=\frac{R_2}{R_1}{R}_3=10\Omega$ within errors.Which of the following is a correct statement?

In a meter bridge the point D is a neutral point (Figure).

Which of the following is correct ?