Physics MCQs for NEET — Practice Questions with Answers

The text states: 'Electric circuits generally consist of a number of resistors and cells interconnected sometimes in a complicated way. The formulae we have derived earlier for series and parallel combinations of resistors are not always sufficient to determine all the currents and potential differences in the circuit. Two rules, called Kirchhoff’s rules, are very useful for analysis of electric circuits.'

The context states: 'Bending or reorienting the wire does not change the validity of Kirchhoff’s junction rule.'

The example provided states: 'It is easily verified that Kirchhoff’s second rule applied to the remaining closed loops does not provide any additional independent equation, that is, the above values of currents satisfy the second rule for every closed loop of the network.'

The context mentions: 'Given a circuit, we start by labelling currents in each resistor by a symbol, say I, and a directed arrow to indicate that a current I flows along the resistor in the direction indicated. Similarly, for each source (i.e., cell or some other source of electrical power) the positive and negative electrodes are labelled.' There is no mention of assuming all resistors are identical.

The context explains: 'This rule is also obvious, since electric potential is dependent on the location of the point. Thus starting with any point if we come back to the same point, the total change must be zero. In a closed loop, we do come back to the starting point and hence the rule.'

According to the context, 'when the atoms come together to form a solid they are close to each other. So the outer orbits of electrons from neighbouring atoms would come very close or could even overlap. This would make the nature of electron motion in a solid very different from that in an isolated atom. ... Because of this, each electron will have a different energy level. These different energy levels with continuous energy variation form what are called energy bands.'

The context states: 'One can have a metal either when the conduction band is partially filled and the balanced band is partially empty or when the conduction and valance bands overlap. When there is overlap electrons from valence band can easily move into the conduction band. This situation makes a large number of electrons available for electrical conduction. ... Therefore, the resistance of such materials is low or the conductivity is high.'

The text explicitly states for insulators, 'a large band gap $E_g$ exists ($E_g > 3 \text{ eV}$). There are no electrons in the conduction band, and therefore no electrical conduction is possible.'

Figure 14.1 description notes: 'The lower band, called the valence band, consists of closely spaced completely filled energy states.' Also, earlier text mentions 'With no external energy, all the valence electrons will reside in the valence band.'

For semiconductors, the text states: 'Here a finite but small band gap ($E_g < 3 \text{ eV}$) exists. Because of the small band gap, at room temperature some electrons from valence band can acquire enough energy to cross the energy gap and enter the conduction band. These electrons (though small in numbers) can move in the conduction band.'