There are two electric bulbs of $40\, W$ and $100\, W$. Which one will be brighter when first connected in series and then in parallel?

Answer the following questions:
$(a)$ $A$ steady current flows in a metallic conductor of non-uniform cross-section. Which of these quantities is constant along the conductor: current, current density, electric field, drift speed?
$(b)$ Is Ohm's law universally applicable for all conducting elements? If not, give examples of elements which do not obey Ohm's law.
$(c)$ $A$ low voltage supply from which one needs high currents must have very low internal resistance. Why?
$(d)$ $A$ high tension $(HT)$ supply of, say, $6 \ kV$ must have a very large internal resistance. Why?

$A$ cell having an emf $\varepsilon$ and internal resistance $r$ is connected across a variable external resistance $R$. As the resistance $R$ is increased,the plot of potential difference $V$ across $R$ is given by:

The value of the resistance $R$ in the figure is adjusted such that the power dissipated in the $2\,\Omega$ resistor is maximum. Under this condition:

$A$ battery is charged at $15\,V$ for $8\,h$ with a current of $10\,A$. During discharge, the battery supplies a current of $5\,A$ for $15\,h$. The terminal voltage during discharge is $14\,V$. Find the watt-hour efficiency of the battery in percentage.

The figure shows a network of four resistances and three batteries. The electrical power dissipated as heat in the circuit is .............. $W$.