Physics MCQs for NEET — Practice Questions with Answers

A diode is a nonlinear device. This means that its current-voltage (I-V) relationship is not a straight line, which indicates that it does not follow Ohm's law across its entire operating range. Instead, a diode allows current to flow easily in one direction (forward bias) while offering high resistance in the opposite direction (reverse bias).

For a bridge rectifier, the peak load voltage ( V_{peak} ) is related to the RMS value of the secondary voltage ( V_{rms} ) by the formula: V_{peak} = V_{rms} imes rac{2}{ ext{sqrt}(2)} . Given that V_{peak} = 40V , we can rearrange this formula to find V_{rms} , which yields approximately 28.3V.

$ V_{rms } = { V_m \over \sqrt 2 } $

In a zener diode, the load current remains approximately constant when the source voltage increases. This is because the zener diode regulates the voltage across the load, ensuring that the load current stays stable even if there are fluctuations in the source voltage.

A varactor diode, also known as a varicap or tuning diode, is specifically designed to act as a variable capacitor when reverse biased. The capacitance of a varactor diode changes with the applied reverse voltage, making it ideal for applications like voltage-controlled oscillators and frequency modulators.

In order for the system to be in equilibrium, the net force on the charge +q at the center must be zero. The four charges extendash Q at the corners of the square create electric fields that cancel each other out at the center. However, the charge +q at the center will experience a force due to each of the -Q charges. The condition for equilibrium dictates that the force due to the central charge must balance the combined forces of the corner charges. Calculating this, we find the correct value of q to be $ - { Q extbackslash over 4 } ( 1 + 2 extbackslash sqrt 2 ) $.