An electron in a metal is free to move anywhere but cannot leave the metal.

There is a frill of $20$ bulbs connected in series in a room. One bulb gets fused. The remaining $19$ are again joined in series and connected to the same supply. Will the light increase or decrease in the room?

$(a)$ Derive an expression to find the equivalent resistance of three resistors connected in series. Also,draw the schematic diagram of the circuit.
$(b)$ Find the equivalent resistance of the following circuit.

An electric heater draws a current of $2\;A$ when connected to a voltage source of $120\;V$. What is the resistance of the heater coil?

Which one of the following is true according to Ohm's law?

The equivalent resistance in series combination is