Question

(i) Two sets $A$ and $B$ of three bulbs each, are glowing in two separate rooms. When one of the bulbs in set $A$ is fused, the other two bulbs also cease to glow. But in set $B$, when one bulb fuses the other two bulbs continue to glow. Explain why this phenomena occurs.
(ii) Why do we prefer to set $B$ for housing circuits?

Answer 1

Hint: In order to solve this question we need to understand about the different combination of resistances like series combination of resistances and parallel combination. In Series combination of resistances all the resistors are connected in series and current that passes through each resistor is the same although there is different voltage assigned to it. In a parallel combination all resistors are connected in parallel then the voltage difference across each resistor is the same but current passes in each resistor is different.

Complete step by step answer:
(i) Let us suppose in set $A$ bulbs or resistors are connected in series and in set $B$ bulbs are connected in parallel with each other. Since we know in series combination current through each is same so if one bulb fuses in set $A$ that means no current can pass through it so other two bulbs do not receive required amount of current to glow and hence ceases to glow

Whereas in set $B$ bulbs are connected in parallel so voltage difference across each is same and current through each is different so if one bulb fuses then it would not affect the other two bulbs current are they are in different row so other two bulbs continue to glow as usual

(ii) We prefer set $B$ means parallel combination in household because:
(a) To keep other devices safe. As stated in parallel combination one device does not affect another so in case any of the electronic devices fuses then it would not affect the other.
(b) To use electronic devices at its full capability. Each device has its own use and it requires a specific amount of current which it can only draw in parallel combination.
So, if any one appliance in the house fails and in order to make other appliances still work we use a parallel combination of wiring and appliances in housing circuits.

Note: It should be remembered that in ideal condition the other two bulbs stop glowing after one bulb fuses in set A but since uncertainty exists everywhere as it is inherent property so other two bulbs luminosity decreases due to less amount of current it receives. Series combination is widely used in circuits to increase net resistance and parallel combination used to decrease net resistance.