Semiconductor Electronics: Materials, Devices and Simple Circuits MCQs for NEET — Physics Questions with Answers

The NCERT text clearly mentions: 'The circuit using two diodes, shown in Fig. 14.19(a), gives output rectified voltage corresponding to both the positive as well as negative half of the ac cycle. Hence, it is known as full-wave rectifier.'

The context explains about full-wave rectifiers: 'So for a full-wave rectifier the secondary of the transformer is provided with a centre tapping and so it is called centre-tap transformer.' While a transformer is often used in half-wave rectifiers for voltage scaling, a center-tapped transformer is a defining feature of the specific full-wave rectifier configuration discussed.

The NCERT states: 'As can be seen from Fig.14.19(c) the voltage rectified by each diode is only half the total secondary voltage.' If $V_{peak}$ is the total secondary voltage, then each diode rectifies $V_{peak}/2$.

The text clearly states: 'This property is used to rectify alternating voltages and the circuit used for this purpose is called a rectifier.' Rectification means converting AC to DC, but specifically, it's a pulsating DC before filtering, which is what the diode achieves.

For a half-wave rectifier, output occurs during one half-cycle for every complete input cycle. So, if the input completes 'f' cycles per second, the output also creates 'f' pulses per second, meaning the fundamental ripple frequency is the same as the input frequency, $f$.

The NCERT text states: '(The reverse breakdown voltage of the diode must be sufficiently higher than the peak ac voltage at the secondary of the transformer to protect the diode from reverse breakdown.)' This implies $V_{BR} > V_{peak}$.

The text states: 'The forward bias resistance is low as compared to the reverse bias resistance. This property is used for rectification of ac voltages as discussed in the next section.'

The context mentions: 'This voltage is called the threshold voltage or cut-in voltage (~0.2V for germanium diode and ~0.7 V for silicon diode).'

The text defines dynamic resistance as: 'For diodes, we define a quantity called dynamic resistance as the ratio of small change in voltage $\Delta V$ to a small change in current $\Delta I$: $r_d = \Delta V / \Delta I$ (14.6)'.

According to the NCERT text, 'In forward bias, the current first increases very slowly, almost negligibly, till the voltage across the diode crosses a certain value. After the characteristic voltage, the diode current increases significantly (exponentially), even for a very small increase in the diode bias voltage.'