Question

In which of these circuits will the lamp glow when the switch is on? Explain the reason in each case?

Answer 1

Hint : When attempting questions like these keep in mind the concepts of series and parallel connection of system. Keep in mind that changing the number of bulbs, or number of batteries in circuit or changing the arrangement of the components; all affect the end result which is whether current passes or not and by how much.

Complete step-by-step solution:
Suppose we have two bulbs connected together in the same circuit. If they are connected in series, then they are connected in such a way that an individual charge would pass through each one of the light bulbs consecutively. When placed in series, charge passes through every light bulb.
Now if we consider parallel arrangement, a single charge passing through the external circuit would only pass through one of the light bulbs. The light bulbs are placed within a separate branch line, and a charge traversing the external circuit will pass through only one of the branches during its path back to the low potential terminal. The means by which the resistors are connected will have a major effect upon the overall resistance of the circuit, the total current in the circuit, and the current in each resistor
In case A, we have a bulb which is connected in parallel to the battery and key. Now, since there is only one bulb in the circuit right now, the bulb will glow when the circuit is switched on. But if we keep on adding more bulbs in parallel, soon there will be a short circuit and no bulb will glow.
In Case B, the batteries are arranged in reverse polarity, hence when the switch is turned on, the bulb would not glow.
In Case C, since the batteries are polar and with the bulb in series, when the switch is turned on the bulb will glow.
To conclude, only Case B will not glow, but both Case A and C will glow.

Note: Other than series and parallel circuit, we also have a third which goes by the name of Combination Circuit, whereas the name suggests, both series and parallel connections are present in the circuit. When you analyze questions regarding the same, it is very important to have a solid, foolproof understanding of concepts regarding series and parallel circuits.