Question

Assertion (A): It is observed that sometimes a bulb glows brighter and sometimes it glows dimly.

Reason (R): Glowing brighter and dimmer depends on the heating effect of the current. More current produces more heating effect making the bulb glow brighter and vice-versa.

• A. Both A and R are true and R is the correct explanation of A.
• B. Both A and R are true but R is not the correct explanation of A.
• C. A is true but R is false.
• D. A is false but R is true.

Answer 1

The correct option is A

Both A and R are true and R is the correct explanation of A.

The explanation for Assertion:

1. It is true that sometimes a bulb grows brighter and sometimes it grows dimmer.
2. This is due to the heating effect of the current.
3. For a steady and fixed current$I$, $H$ is the amount of heat that is produced in time $t$ is $H=V\times I\times t$, $V$ is the voltage.
4. When more current flows through the bulb for some time, it gets hot and thus glows brighter.
5. Similarly, when less current flows the bulb does not get hot and is dimmer.

The explanation for reason:

1. When a current passes through a conductor for a long time, after some time the conductor becomes hot.
2. Due to this, heat is produced through the conductor.
3. This is called the heating effect of the conductor.
4. Joule’s law of heating is given by $H=I^{2}Rt$
   Where $H$ is the amount of heat produced, $I$ is the current flow, $R$ is the resistance offered by the conductor and the $t$ is the time taken.
5. The lumen of the bulb depends on the current flowing through the bulb element.
6. The heat produced by the bulb is proportional to the product of the square of the current and the resistance.
7. So, the heating effect depends on the current and resistance passed through the conductor.
8. If there is more resistance that means more voltage at the same current and constantly more power which helps the bulb to glow brighter.
9. The more the current is passed, the more will be the heating effect and in turn, the brighter the bulb will glow.

Thus, both assertion and reason are true and Reason is the correct explanation of Assertion.

Hence, option (A) is the correct answer.