Physics MCQs for NEET — Practice Questions with Answers

Given \(P = 100 W\) and \(V_{rms} = 220 V\). We know \(P = I_{rms} V_{rms}\). Therefore, \(I_{rms} = P / V_{rms} = 100 W / 220 V \approx 0.454 A\). This is directly from Example 7.1 (c).

The NCERT text derived this: 'Using the trigonometric identity, \(sin^2 \omega t = 1/2 (1– cos 2\omega t)\), we have \(\langle sin^2 \omega t \rangle = (1/2) (1– \langle cos 2\omega t \rangle)\) and since \(\langle cos 2\omega t \rangle = 0\), we have, \(\langle sin^2 \omega t \rangle = 1/2\)' (Eq. 7.5c).

The 'Points to Ponder' section clarifies: 'Though in a phasor diagram, voltage and current are represented by vectors, these quantities are not really vectors themselves. They are scalar quantities. It so happens that the amplitudes and phases of harmonically varying scalars combine mathematically in the same way as do the projections of rotating vectors... The ‘rotating vectors’ that represent harmonically varying scalar quantities are introduced only to provide us with a simple way of adding these quantities using a rule that we already know as the law of vector addition.'

According to the NCERT text, 'The specific heat capacity is the property of the substance which determines the change in the temperature of the substance (undergoing no phase change) when a given quantity of heat is absorbed (or given off) by it. It is defined as the amount of heat per unit mass absorbed or given off by the substance to change its temperature by one unit.' Mathematically, it is expressed as $s = \frac{1}{m} \frac{\Delta Q}{\Delta T}$.

The NCERT text states, 'The SI unit of molar specific heat capacity is J mol$^{-1}$ K$^{-1}$'. J kg$^{-1}$ K$^{-1}$ is the unit for specific heat capacity (per unit mass).

From the NCERT text: 'For a mole of a solid, the total energy is $U = 3 k_B T \times N_A = 3 RT$. Now, at constant pressure, $\Delta Q = \Delta U + P \Delta V \cong \Delta U$, since for a solid $\Delta V$ is negligible. Therefore, $C = \frac{\Delta Q}{\Delta T} = \frac{\Delta U}{\Delta T} = 3R$'. This value generally agrees with experimental values at ordinary temperatures.

The NCERT text states, 'The specific heat capacity is the property of the substance... It depends on the nature of the substance and its temperature.' It does not depend on the amount of substance.

The NCERT text explains: 'However, in connection with specific heat capacity of gases, additional conditions may be needed to define C. In this case, heat transfer can be achieved by keeping either pressure or volume constant. If the gas is held under constant pressure during the heat transfer, then it is called the molar specific heat capacity at constant pressure and is denoted by $C_p$. On the other hand, if the volume of the gas is held constant, it is denoted by $C_v$.'

Specific heat capacity is defined as the amount of heat per unit mass required to change its temperature by one unit. Therefore, 4186 J kg$^{-1}$ K$^{-1}$ means that 4186 Joules of heat energy are needed to raise the temperature of 1 kg of water by 1 Kelvin (or 1 degree Celsius).

From the NCERT text: 'The old unit of heat was calorie. One calorie was earlier defined to be the amount of heat required to raise the temperature of 1g of water by 1°C.' It further refines this to '1g of water from 14.5 °C to 15.5 °C' for a precise definition.