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NEET Practice Questions (MCQs) with Answers & Solutions

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In a full-wave rectifier using a center-tap transformer, if the peak AC voltage across the entire secondary winding is $V_{peak}$, what is the peak voltage rectified by each diode?

A. $V_{peak}$ B. $V_{peak}/2$ C. $2V_{peak}$ D. Depends on the load resistor

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Explanation

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 $V_{peak}/2$.

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What is the primary function of a rectifier circuit?

A. To convert DC voltage into AC voltage. B. To amplify the input AC signal. C. To convert AC voltage into pulsating DC voltage. D. To filter out unwanted noise from an AC signal.

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Explanation

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.

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In a half-wave rectifier, if the input AC frequency is $f$, what is the frequency of the ripple in the output voltage?

A. $f/2$ B. $f$ C. $2f$ D. Zero, as it's DC

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Explanation

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, $f$.

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To protect a diode from reverse breakdown in a rectifier circuit, what condition must be met regarding the reverse breakdown voltage ($V_{BR}$) and the peak AC voltage ($V_{peak}$) at the secondary of the transformer?

A. $V_{BR} < V_{peak}$ B. $V_{BR} = V_{peak}$ C. $V_{BR} > V_{peak}$ D. They are unrelated.

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Explanation

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 $V_{BR} > V_{peak}$.

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What is the relationship between forward bias resistance and reverse bias resistance of a p-n junction diode according to the provided text?

A. Forward bias resistance is higher than reverse bias resistance. B. Forward bias resistance is equal to reverse bias resistance. C. Forward bias resistance is low as compared to the reverse bias resistance. D. Resistance is constant regardless of bias.

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Explanation

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.'

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What is the approximate threshold voltage for a silicon diode mentioned in the text?

A. ~0.2 V B. ~0.7 V C. ~1.2 V D. ~0.0 V

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Explanation

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).'

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The dynamic resistance ($r_d$) of a diode is defined as:

A. $V/I$ B. $\Delta I / \Delta V$ C. $\Delta V / \Delta I$ D. The constant resistance in both forward and reverse bias.

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Explanation

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)'.

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Which of the following characteristics is NOT typically found in Reptilia?

A. Poikilothermous nature B. Body covered by dry and cornified skin C. Presence of external ear openings D. Internal fertilization

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Explanation

According to the NCERT text, 'They do not have external ear openings. Tympanum represents ear.' Therefore, the presence of external ear openings is not a characteristic of Reptilia.

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The locomotion mode from which the class Reptilia derives its name literally means:

A. To fly or soar B. To swim or glide C. To creep or crawl D. To jump or hop

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Explanation

The context states: 'The class name refers to their creeping or crawling mode of locomotion (Latin, repere or reptum, to creep or crawl).'

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Identify the INCORRECT match regarding examples of Reptilia:

A. Chelone - Turtle B. Testudo - Tortoise C. Naja - Viper D. Crocodilus - Crocodile

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Explanation

The NCERT text lists 'Naja (Cobra)' as a poisonous snake, while 'Vipera (Viper)' is another distinct example. Naja is Cobra, not Viper.

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