Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Rutherford's model has electrons that move in circles round the nucleus.
In Bohr's model, electrons move only in fixed shells, K, L, M, N, each with a fixed energy. An electron in a shell does not lose energy. A jump to a higher shell takes in energy; a fall to a lower shell gives out the difference as light. In hydrogen, the levels are K , L , M and N .
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The problem. A charged particle moving in a circle should keep losing energy as light.
Step 2. What would follow. The electron would spiral into the nucleus in a tiny fraction of a second, and every atom would collapse. But atoms are stable.
Step 3. Bohr's change. Electrons move only in certain fixed shells. In those shells, they do not lose energy. They take in or give out energy only when they jump from one shell to another.
Answer: (a) The electrons should lose energy and fall into the nucleus. (b) Fixed shells in which no energy is lost.
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