Question

The source of energy in the Sun is:

• A. Conversion of hydrogen into helium in nuclear fusion reaction.
• B. Uranium fission.
• C. Beta decay of uranium.
• D. Reaction of hydrogen with uranium.

Hint:

Nuclear fusion, where hydrogen is converted into helium, is the primary energy source in stars, including the Sun.

Answer 1

The Correct Option is A

The Sun is made up mostly of hydrogen, with helium as the next most common element.

Under the huge pressure and temperature at its core, about 15 million kelvin, hydrogen nuclei are pushed close enough together to fuse, eventually combining four hydrogen nuclei into one helium nucleus.

The mass of the resulting helium nucleus is slightly less than the combined mass of the four hydrogen nuclei that formed it, and this missing mass is released as energy according to \( E = mc^2 \).

Since the Sun has almost no uranium, processes like fission or the decay of uranium cannot account for its energy output.

Final Answer:
The Sun's energy comes from the fusion of hydrogen into helium.

Answer 2

A different way to confirm the source of the Sun's energy is to look at how long the Sun has been shining and check which process could sustain that for so long.

1. Conversion of hydrogen into helium in nuclear fusion: The Sun has been radiating energy for about 4.6 billion years, and the sheer quantity of hydrogen in its core, combined with the huge energy release per fusion event, is enough to power it at its observed brightness for billions of years.
2. Uranium fission: Even if some uranium were present in the Sun, the total amount would be far too small compared to the Sun's mass to explain billions of years of steady energy output.
3. Beta decay of uranium: This process releases energy far too slowly and in far too small a quantity to match the Sun's actual energy output, and again there simply is not enough uranium in the Sun for this to matter.
4. Reaction of hydrogen with uranium: No known nuclear process works this way, and the scarcity of uranium in the Sun rules this option out regardless.

Only fusion of hydrogen into helium, fed by the Sun's enormous hydrogen supply, can account for the Sun shining steadily for billions of years.

Therefore, the correct answer is conversion of hydrogen into helium in nuclear fusion reaction.