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In proton - proton cycle in Sun the energy released when an electron and its antiparticle combines is ______.

Asked in GUJCET 2023 · Energy released in fission and fusion

• (1) 1.021×10⁻¹³ J
• (2) 0.672×10⁻¹³ J
• (3) 1.126×10⁻¹³ J
• (4) 1.632×10⁻¹³ J

Step-by-step solution

Why the other options are wrong

• (1) 1.021×10⁻¹³ carries the MeV figure straight into the joule slot: the step releases 1.02 MeV, and the conversion 1 MeV=1.6×10⁻¹³ J still has to be applied.
• (2) 0.672×10⁻¹³ J is 0.42 MeV — the energy of the first step of the cycle, ¹₁H+¹₁H→²₁H+e⁺+ u, not of the annihilation.
• (3) 1.126×10⁻¹³ J works back to 0.70 MeV, which is not the energy of any step of the proton-proton cycle. Sanity check: annihilation releases 2mₑc²=2×0.511=1.02 MeV=1.632×10⁻¹³ J.

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