Physics MCQs for NEET — Practice Questions with Answers

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.

According to the NCERT text, 'The equivalent internal resistance of a series combination of n cells is just the sum of their internal resistances.' (Eq. 3.46 for two cells extends to n cells).

The NCERT text states, 'Consider first two cells in series (Fig. 3.13), where one terminal of the two cells is joined together leaving the other terminal in either cell free. ...eeq = $\epsilon_1$ + $\epsilon_2$' (Eq. 3.45). This refers to the arrangement where the negative of one is connected to the positive of the other, resulting in additive emfs.

The NCERT text mentions: 'If instead we connect the two negatives, Eq. (3.42) would change to $V_{BC} = -\epsilon_2 - Ir_2$ and we will get $e_{eq} = \epsilon_1 - \epsilon_2$ (${\epsilon_1} > {\epsilon_2}$)' (Eq. 3.47). This indicates that when cells are connected in opposition (e.g., negative to negative or positive to positive), their emfs subtract.

The NCERT text states, 'The equivalent internal resistance of a series combination of n cells is just the sum of their internal resistances.' For n identical cells, $r_{eq} = r + r + ... + r$ (n times) $= n r$.

For cells in parallel (Figure 3.14), the NCERT text states, 'At the point B1, I1 and I2 flow in whereas the current I flows out. Since as much charge flows in as out, we have $I = I_1 + I_2$' (Eq. 3.48). This follows Kirchhoff's current rule (junction rule).

According to the NCERT text, for a parallel combination of n cells, the equivalent internal resistance is given by ' $1/r_{eq} = 1/r_1 + ... + 1/r_n$' (Eq. 3.58).