What is the work done by the field of a nucleus in complete circular orbit of the electron and what if the orbit is elliptical?

Q. In addition to radial distance from the nucleus, what is the other factor, which changes in an elliptical orbit?

Q. Under what condition an elliptical orbit corresponds to circular orbit?

Q. Consider a planet moving in an elliptical orbit round the sun. The work done on the planet by the gravitational force of the sun
(a) is zero in any small part of the orbit
(b) is zero in some parts of the orbit
(c) is zero in one complete revolution
(d) is zero in no part of the motion.

Q. In an Hydrogen like atom, the electron moves around the nucleus in circular orbits of radius $R$. It is excited to the orbit of radius $4R$. The ratio of the time taken by the electron to complete one revolution in the orbit of radius $R$ to that of orbit of radius $4R$ is:

Q. As per Bohr's model, an electron in an uni-electronic species revolves around the nucleus in circular orbits. What is the radius of the 3rd orbit of $H{e}^{+}$ ion?