What is the magnitude of the electric charge on an electron?

The $V-I$ graphs for two wires $A$ and $B$ are shown in the figure. If we connect both the wires one by one to the same battery, which of the two will produce more heat per unit time? Give justification for your answer.

What is the cause of resistance?

$A$ bulb is rated $220\;V$ and $100\;W$. What is the resistance of this bulb?

Three bulbs of $40\, W$,$60\, W$,and $100\, W$ are connected in series across the mains. Across which bulb is the potential difference highest? Across which is it lowest?

Two wires of the same metal have the same length, but cross-sections are in the ratio $3 : 1$. They are joined in series. The resistance of the thicker wire is $10\, \Omega$. The total resistance of the combination will be: