# Scientific notation and usage thereof [closed]

I'm taking my first physics exam in university this Saturday, and I'm currently working on a practice exam.

I got the answer 3.1MeV for a alpha-decay question, but the answer was 3100keV. I understand that they represent the same thing, but why is my way of answering discouraged? Are there actual reasons? Might I lose points on my exam for answering like I did here?

EDIT: 0.31MeV is not equal to 3100keV...

## closed as off-topic by ZeroTheHero, Kyle Kanos, Chemomechanics, John Rennie, Jon CusterJan 18 at 14:18

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – ZeroTheHero, Chemomechanics, John Rennie
If this question can be reworded to fit the rules in the help center, please edit the question.

• I've added the homework-and-exercises tag. In the future, please use this tag on this type of question. – Ben Crowell Jan 17 at 15:54
• "I understand that they represent the same thing," No, they are a factor of 10 different. You would certainly lose marks for making that mistake! – alephzero Jan 17 at 16:00
• Then what the question is now? – Alchimista Jan 17 at 16:18
• Fundamentally we can't answer questions about why your paper was marked as it was. In the absence of explicit instructions to answer in $\mathrm{keV}$ I would have accepted $3.1\,\mathrm{MeV}$. – dmckee Jan 18 at 2:31

• @PhilipWood I didn't downvote, but "significant figures" are not a very serious method of showing accuracy, except in school work. "Using a large unit" doesn't help if you want to express things like $3100 \pm 60$ keV or $3100$ keV $\pm 10$%. – alephzero Jan 17 at 20:40