NEET Practice Questions (MCQs) with Answers & Solutions

The NCERT suggests specific measures: 'This can be achieved by avoiding stagnation of water in and around residential areas, regular cleaning of household coolers, use of mosquito nets, introducing fishes like Gambusia in ponds that feed on mosquito larvae, spraying of insecticides in ditches, drainage areas and swamps, etc.'

The summary states, 'An overall improvement in reproductive health has taken place in our country as indicated by reduced maternal and infant mortality rates, early detection and cure of STIs, assistance to infertile couples, etc.'

The introductory text mentions, 'The discovery of antibiotics, and synthetic plant-derived drugs, anaesthetics have changed medical practice on one hand and human health on the other hand. Life expectancy of human beings have dramatically changed over the years.'

According to the NCERT text and Figure 7.2, 'In a pure resistor, the voltage and current are in phase. The minima, zero and maxima occur at the same respective times.' This means their phase difference is zero.

The NCERT states, 'the sum of the instantaneous current values over one complete cycle is zero, and the average current is zero.' This is because the sinusoidal current has symmetrical positive and negative values over a cycle.

From the NCERT text, 'In terms of I, the average power, denoted by P is \(P = I^2 R\)' (Eq. 7.7). It also states, 'Equation (7.7) can also be written as \(P = V^2 / R = I V\) (since \(V = I R\)'). Here, I and V represent rms values. Therefore, all options represent valid formulas for average power in a purely resistive AC circuit.

The 'Points to Ponder' section explicitly states, '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.' In the example, 220 V is also used as an RMS value.

The NCERT text states that the relation between RMS voltage (V) and peak voltage (\(V_m\)) is \(V = V_m / \sqrt{2}\). Therefore, \(V_m = V \sqrt{2}\). Given \(V = 220 V\), then \(V_m = 220 \times 1.414 \approx 311 V\).

Equation 7.6 defines RMS current: '\(I = i_m / \sqrt{2} = 0.707 i_m\)'.

The NCERT states, 'This shows the advantage of introducing the concept of rms values. 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.'