One thing arrives
Show on a big screenEvery fire on Earth could go out. The days would still be warm.
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The rule
Sunlight's energy is intensity × area × time. This holds while the intensity stays steady.
Intensity is the energy landing on 1 m² each second. The area faces the Sun. Energy (E) is counted in joules (J).
- The Sun sends light out in every direction.
- Only a tiny share is aimed toward Earth.
- Nothing carries it across the empty space between.
- That small share still powers weather and life here.
The idea
Sunlight is solar radiation, the main energy source on Earth. It travels as electromagnetic waves. These cross empty space at 3 × 10⁸ m/s. Sunlight takes about 8 minutes to reach us.
Insolation is the sunlight that lands on the ground. At most, it is about 1 kW on each m². Here 1 kW means 1000 J each second.
| Step | Working |
|---|---|
| The rule | E = intensity × area × time |
| Intensity | 1 kW is 1000 J each second, on every m² |
| Area and time | 2 m², and 2 hours is 7200 s |
| Working | E = 1000 × 2 × 7200 |
| Answer | 14,400,000 J = 1.44 × 10⁷ J |
Suppose the sky stays clear and the Sun stays high. Then the sunlight on the panel carries 4 units of energy. One unit is 3,600,000 J. Check: 14,400,000 ÷ 3,600,000 = 4. A panel turns only part of it into electricity. A home bill counts electricity in these units.
Try the lab to finish this lesson.