Q67 / 270 · NDA 2026 (Phase 1) · General Ability
A lightning rod with sharp tip reduces damage risk. Which one of the following is the primary reason for it?
- AIt attracts lightning directly.
- BThe sharp tip reduces the local electric field.
- Correct answerCIt enhances field and promotes continuous corona discharge.
- DIt repels charged clouds.
Solution
A lightning rod has a sharp tip, which means the radius of curvature at the tip is very small.
Since surface charge density $\sigma$ is inversely proportional to the radius of curvature, the charge density at the sharp tip becomes very high.
The electric field near the surface of a conductor is given by $E = \dfrac{\sigma}{\epsilon_0}$. Thus, the intense charge density creates a very strong local electric field.
This strong electric field ionizes the surrounding air molecules, leading to a continuous corona discharge. This discharge helps in partially neutralizing the charge of the cloud and provides a conducting path for the lightning to safely reach the ground, thereby reducing the risk of damage.
Answer: It enhances field and promotes continuous corona discharge.
Since surface charge density $\sigma$ is inversely proportional to the radius of curvature, the charge density at the sharp tip becomes very high.
The electric field near the surface of a conductor is given by $E = \dfrac{\sigma}{\epsilon_0}$. Thus, the intense charge density creates a very strong local electric field.
This strong electric field ionizes the surrounding air molecules, leading to a continuous corona discharge. This discharge helps in partially neutralizing the charge of the cloud and provides a conducting path for the lightning to safely reach the ground, thereby reducing the risk of damage.
Answer: It enhances field and promotes continuous corona discharge.
Hence, the correct answer is option: 'C'.