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# Physics - calculations watch

1. The question (#1) says "the energy yield is only 10 millionths of the energy delivered by the laser (the efficiency is equal to 10^-5)"
You are actually dividing the 40J by 10 million (10^5) which is the same as multipling by 10^-5.
2. (Original post by Stonebridge)
The question (#1) says "the energy yield is only 10 millionths of the energy delivered by the laser (the efficiency is equal to 10^-5)"
You are actually dividing the 40J by 10 million (10^5) which is the same as multipling by 10^-5.
Okay let me see if i get this now then.... an energy of 40J is inputted basically, this provides the binding energy needed for the nucleons to split to form a bigger nucleus(fusion). Then we are told the energy YIELD is 10 millionths of the energy delivered which is 40J. As you said you do 40*10^-5 to get the total energy yield. We divide this by the binding energy to get the number of atoms involved in this fusion process and since there is 2 atoms deuterium involved you multiply by two to get the answer. Correct?
3. Correct.
The answer is given in the question as "about 10^9" to emphasise that the whole thing is a bit of an approximation, using guesswork for the efficiency of one in 10 million, for example.
It's what's called an "order of magnitude" calculation. A ball-park figure.
4. (Original post by Stonebridge)
Correct.
The answer is given in the question as "about 10^9" to emphasise that the whole thing is a bit of an approximation, using guesswork for the efficiency of one in 10 million, for example.
It's what's called an "order of magnitude" calculation. A ball-park figure.
Oh, i know about the approximation part, never knew the technical name for it.... just googled it and makes sense to call it. Thanks mate, much appreciated!!!! the thing confused me when it said it produces 40J and then used these easy questions to throw you off from the major question. But now i get these type of questions so thank you for that

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