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I was reading about the power radiated by an oscillating electric dipole. It then said that monopoles don't radiate.

But a monopole is just a charge, right? And an accelerated charge radiates EM waves. Can someone please explain.

Qmechanic
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Matrix23
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  • If you'd like an explanation of the item you are reading, then can you block-quote the relevant "monopoles don't radiate" section here? – uhoh Oct 28 '17 at 02:22
  • Possible duplicates: https://physics.stackexchange.com/q/329292/2451 , https://physics.stackexchange.com/q/139819/2451 and links therein. – Qmechanic May 02 '21 at 08:24

1 Answers1

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Dipoles can radiate because a time changing electric dipole moment does not violate the conservation of charge (you can think of the two opposite charges rapidly changing places with time). However, for the value of an electric monopole (a single charge) to change with time without there being any other charge in the region, conservation of charge would have to be violated; Which is impossible.

Edit: I don't think that the author of what you're reading means an accelerating charge; just like us not considering accelerating dipoles when we are talking about dipole radiation.

Sahand Tabatabaei
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  • can you please explain how conservation of charge is violated when one shakes a single charge? – ZeroTheHero Oct 24 '17 at 02:42
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    Shaking a single charge falls in the category of accelerating charges which as I said, is probably not what the author was talking about (of course any accelerating charge radiates). Just like when we say dipole radiation we don't talk about an accelerating dipole, but just a stationary dipole with a time varying dipole moment. Similarly, a stationary point charge cannot have a time changing monopole (charge) because charge must be conserved. – Sahand Tabatabaei Oct 24 '17 at 03:09