Kepler's third law (Law of Periods) gives the relation between the time period T and semi-major axis a of a planetary orbit as:
AT² ∝ a
BT² ∝ a²
CT² ∝ a³
DT ∝ a³
Answer & Solution
Correct answer: C. T² ∝ a³
1. Kepler's third law: square of the period of revolution is proportional to the cube of the semi-major axis.
2. T² ∝ a³, i.e. T² = k a³ where k is a constant for all planets of the Solar System.
3. This is confirmed in Table 7.1 of NCERT, where T²/a³ is nearly the same for all eight planets.
_Source: NCERT Class 11 Physics Ch 7 "Gravitation", §7.2 (Law of Periods + Table 7.1), p. 128–129_
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