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Fundamentals Of Physics
Found in: Page 1332

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Short Answer

We have seen that Q for the overall proton–proton fusion cycle is 26.7 MeV. How can you relate this number to the Q values for the reactions that make up this cycle, as displayed in Fig. 43-11?

The given Q-value 26.7 MeV is the total energy of the proton-proton fusion cycle.

See the step by step solution

Step by Step Solution

Step 1: Write the given data

The Q-values for the individual reactions of the proton-proton fusion cycle in figure 43-11 are given.

Step 2: Determine the concept of Q-value

The Q-value of the fusion process is the amount of energy that is either absorbed or released during the process. Thus, it describes the integration process for a fusion process that involves the binding of two nuclei.


The Q-value of a given full cycle is the sum of all the energy (or Q-value) of the reactions that contribute to the full cycle reaction as follows:

Q=inQi …… (i)

Step 3: Calculate the Q-value of the overall proton-proton fusion cycle

Let, the Q-values of all the given individual reactions be Q1=0.42 MeV, Q2=1.02 MeV Q3=5.49 MeV and Q4=12.86 MeV. Thus, for the overall proton-proton fusion cycle, the total Q-value can be calculated using equation (i) as follows:

Q=2Q1+2Q2+2Q3+Q4 =20.42 MeV+1.02 MeV+5.49 MeV+12.86 MeV =26.7 MeV

Hence, the given value 26.7 MeV is the total energy of the proton-proton fusion cycle.

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