A car parked in bright sunlight with all its windows closed becomes extremely hot inside. Which phenomenon mainly explains this effect?

Introduction / Context:
Many people have experienced how hot the interior of a parked car can become on a sunny day, especially when all windows are closed. This is not mainly due to the engine but due to a physical process similar to the greenhouse effect. Understanding this everyday phenomenon helps link basic physics concepts about radiation and heat transfer to real life safety issues.

Given Data / Assumptions:

• The car is parked in sunlight with its engine off.
• All windows are closed, and sunlight enters through the glass.
• We are concerned with the reason the interior air temperature rises significantly.

Concept / Approach:
Sunlight, especially visible and short wavelength solar radiation, passes easily through glass windows and is absorbed by the car interior surfaces such as seats and dashboard. These surfaces heat up and re radiate energy mainly as longer wavelength infrared radiation. Glass is relatively less transparent to this infrared radiation, so the heat tends to be trapped inside. This trapping of heat due to selective transmission and absorption is known as the greenhouse effect, analogous to what happens in a greenhouse or in the Earth atmosphere with certain gases.

Step-by-Step Solution:
Step 1: Sunlight enters the car through transparent windows and is absorbed by interior surfaces. Step 2: The absorbed energy raises the temperature of the seats, dashboard, and other interior elements. Step 3: These hot surfaces emit infrared radiation, which is partly blocked or reflected by the glass windows. Step 4: Because the heat gets trapped and cannot easily escape, the interior temperature climbs much higher than the outside temperature.

Verification / Alternative check:
You can verify this by comparing a car with windows slightly open to one with windows fully closed under the same conditions. The car with slight ventilation will usually be cooler, because hot air can escape. The strong effect of glass in trapping heat can be observed similarly in greenhouses where plants are grown in cold environments. The same physical principles apply, reinforcing that this is an example of the greenhouse effect.

Why Other Options Are Wrong:
Heat produced by the engine: In a parked car with the engine off, engine heat is not the main source; the major heating comes from solar radiation. Good conducting power of the metal body: Metal conduction distributes heat but does not by itself create the strong temperature rise inside. The double layered windscreen: This can influence insulation, but the key mechanism is selective transmission and trapping of radiation, which is the greenhouse effect.

Common Pitfalls:
People often think heat simply accumulates because the car is a closed space, ignoring the role of radiation and glass properties. Others may confuse conduction with radiation. Remember that the greenhouse effect involves short wavelength solar radiation entering easily and long wavelength infrared radiation being partially blocked, causing heat build up. This concept appears in many exam questions about climate change and everyday physics.

Final Answer:
The main reason a closed car becomes so hot in sunlight is due to the greenhouse effect.