NEET Practice Questions (MCQs) with Answers & Solutions

The context states: 'If the substance is in the form of a long rod, then for small change in temperature, $\Delta T$, the fractional change in length, $\Delta l/l$, is directly proportional to $\Delta T$. where $\alpha_l$ is known as the coefficient of linear expansion (or linear expansivity)...'

The context explicitly states: 'The relation between them is : $\alpha_V = 3\alpha_l$'.

From Table 10.1, $\alpha_l$ for Glass (pyrex) is $0.32 \times 10^{-5} K^{-1}$ and for Copper is $1.7 \times 10^{-5} K^{-1}$. Comparing these, $1.7 / 0.32 \approx 5.3$, so copper expands about five times more than glass.

The context defines this phenomenon: 'What happens by preventing the thermal expansion of a rod by fixing its ends rigidly? Clearly, the rod acquires a compressive strain due to the external forces provided by the rigid support at the ends. The corresponding stress set up in the rod is called thermal stress.'

The context mentions: 'Similarly, in case of gases, a balloon partially inflated in a cool room may expand to full size when placed in warm water.' This describes the volume expansion of the air (a gas) inside the balloon.

The definition $\Delta l/l = \alpha_l \Delta T$ implies that $\alpha_l = (\Delta l/l) / \Delta T$. Since $\Delta l/l$ is dimensionless, the unit of $\alpha_l$ is the inverse of the unit of temperature change, which is $K^{-1}$ (or $^\circ C^{-1}$). The table also lists units as $10^{-5} K^{-1}$.

The context states: 'Normally, metals expand more and have relatively high values of $\alpha_l$.' Table 10.1 confirms metals like Aluminium, Brass, Iron, Copper, Silver, Gold have higher values compared to Glass (pyrex) and Lead.

The example for area expansion shows that when the temperature increases by $\Delta T$, 'a' increases by $\Delta a = \alpha_l a \Delta T$ and 'b' increases by $\Delta b = \alpha_l b \Delta T$. This directly refers to linear expansion.

The introduction section mentions: 'you will find out why blacksmiths heat the iron ring before fitting on the rim of a wooden wheel of a horse cart'. This is a classic application of thermal expansion, where the ring expands on heating, allowing it to fit, and then contracts on cooling, forming a tight fit.

The text states: 'The inheritance of flower colour in the dog flower (snapdragon or Antirrhinum sp.) is a good example to understand incomplete dominance.' In incomplete dominance, the F1 phenotype is intermediate between the two parental phenotypes.