Q 11-10-005NEETNEET 2020Top questionEasy
The quantities of heat required to raise the temperature of two solid copper spheres of radii $r_1$ and $r_2$ ($r_1 = 1.5r_2$) through $1$ K are in the ratio :
Answer: (A) $\dfrac{27}{8}$
Concept. $Q = mc\Delta T$. Same material and same $\Delta T$, so $Q \propto m \propto r^3$.
Step 1. Ratio.
$$\frac{Q_1}{Q_2} = \left(\frac{r_1}{r_2}\right)^3 = (1.5)^3 = \frac{27}{8}$$
Answer. $\dfrac{27}{8}$ (Option A).
Solution by Sreeraj P, M.Sc Physics