When an electric bulb accidentally breaks, a small explosive-like sound is heard. This sound is mainly due to which of the following reasons?

Introduction / Context:
Many electric bulbs are either evacuated or filled with gas at a pressure different from the surrounding air. When such a bulb breaks, people often hear a sharp, explosive-like sound. This question tests your understanding of pressure differences and how they can cause a sudden movement of air that produces noise when the thin glass envelope of a bulb shatters.

Given Data / Assumptions:

• An electric bulb has a thin glass shell.
• Inside the bulb there is usually a partial vacuum or low pressure gas.
• The surrounding atmosphere is at normal atmospheric pressure, which is higher than the pressure inside the bulb.
• The bulb breaks suddenly, creating an opening between inside and outside.

Concept / Approach:
If there is a pressure difference between two regions separated by a barrier, removing or breaking that barrier causes the fluid (here, air) to rush from the higher pressure region to the lower pressure region. In the case of a typical bulb, the inside is at lower pressure, and the outside is at higher atmospheric pressure. When the glass breaks, external air rapidly moves inward to fill the low pressure region, producing a sharp sound due to the sudden rush and the shattering glass. There is no significant chemical reaction between gases, and the inner gas is not highly compressed in the way described in some of the incorrect options.

Step-by-Step Solution:
Step 1: Recognise that many bulbs are partially evacuated or contain a small amount of inert gas at a pressure lower than atmospheric pressure. Step 2: Understand that the outside air pressure is higher than the pressure inside the bulb. Step 3: When the glass bulb breaks, the barrier between these two pressure regions disappears almost instantly. Step 4: High pressure air from the outside rushes into the bulb to equalise the pressure, and this sudden inward flow produces a sharp sound and contributes to the shattering effect. Step 5: Therefore, the correct explanation is that the air outside rushes in to fill the vacuum or low pressure region inside the bulb.

Verification / Alternative check:
If the bulb interior were at higher pressure than the outside, we would expect gases to rush outward, and the sound pattern and glass fragments would be different. However, typical incandescent and some other types of bulbs are designed with low pressure or slight vacuum to reduce oxidation of the filament and improve efficiency. Physics and engineering references confirm that the slight “pop” heard is mainly due to air rushing inward and the mechanical fracture of the glass. There is no rapid chemical reaction that would resemble an explosion in such bulbs under normal conditions.

Why Other Options Are Wrong:
A chemical reaction between the gases inside the bulb: The gases inside (often inert gases like argon or nitrogen) are chosen specifically for their low reactivity, so explosive chemical reactions are not expected.

Compressed gases inside rushing out suddenly: The interior is at lower, not higher, pressure than the outside. Thus, the direction of flow is from outside to inside, not the reverse.
None of these: This is incorrect because there is a clear physical explanation involving air rushing in.

Common Pitfalls:
Students sometimes imagine that the bulb contains highly compressed gas which “explodes” outward, but this is not typical for household bulbs. Another misunderstanding is blaming vague “chemical reactions” whenever a sudden sound occurs. In reality, pressure differences are often enough to cause loud noises when containers rupture. Remember that the greater outside atmospheric pressure forces air into the bulb when it breaks, producing the characteristic popping sound.

Final Answer:
The explosive-like sound when a bulb breaks is mainly due to air outside rushing in suddenly to fill the vacuum inside the bulb.