Physics MCQs for NEET — Practice Questions with Answers

The context explicitly mentions, 'It is customary to measure and specify rms values for ac quantities. For example, the household line voltage of 220 V is an rms value'. This confirms that such general ratings refer to RMS values.

The text provides the calculation: '$V_m = \sqrt{2} V = (1.414)(220 V) = 311 V'$. This shows how to convert from RMS voltage to peak voltage.

The text states: 'In terms of I, the average power, denoted by P is $P = I_m^2 R/2 = I^2 R$'. It also mentions, 'In terms of rms values, the equation for power [Eq. (7.7)] and relation between current and voltage in ac circuits are essentially the same as those for the dc case.' This supports $P=I^2R$ as the equivalent expression.

As stated in 'POINTS TO PONDER 1.', 'When a value is given for ac voltage or current, it is ordinarily the rms value. The voltage across the terminals of an outlet in your room is normally 240 V. This refers to the rms value of the voltage.' Similarly, the 220V rating for the bulb in example 7.1 is an RMS value.

From Example 7.1(a): 'We are given P = 100 W and V = 220 V. The resistance of the bulb is $R = V^2 / P = (220 V)^2 / 100 W = 48400 / 100 \Omega = 484 \Omega$'.

From Example 7.1(c): 'Since, $P = I V$, then $I = P / V = 100 W / 220 V = 0.454 A$'.

The context states: 'Thus, the sum of the instantaneous current values over one complete cycle is zero, and the average current is zero.' This is because for every positive value, there is a corresponding negative value.

The table for physical quantities and remarks states: 'rms voltage $V = \frac{V_m}{\sqrt{2}}$, $V_m$ is the amplitude of the ac voltage.' This directly provides the relationship.

The 'POINTS TO PONDER 4.' section states: 'Joule heating is such a property, and there is one ampere of rms value of alternating current in a circuit if the current produces the same average heating effect as one ampere of dc current would produce under the same conditions.'

From 'POINTS TO PONDER 2.', 'The power rating of an element used in ac circuits refers to its average power rating.' From 'POINTS TO PONDER 3.', 'The power consumed in an ac circuit is never negative.' And from the example 7.2 explanation, 'Thus, the average power supplied to an inductor over one complete cycle is zero.' However, Case (iv) under power factor discusses LCR series circuit at resonance: 'At resonance Xc – XL= 0, and φ = 0. Therefore, cos φ = 1 and P = I^2Z = I^2R. That is, maximum power is dissipated in a circuit (through R) at resonance.' Thus, option 4 is incorrect.