Science (English Medium) Class 12 - CBSE Question Bank Solutions

What happens during regulation action of a Zener diode?

1. The current in and voltage across the Zenor remains fixed.
2. The current through the series Resistance (R_s) changes.
3. The Zener resistance is constant.
4. The resistance offered by the Zener changes.

With the help of a neat circuit diagram, explain the working of a photodiode. 

Two parallel-plate capacitors X and Y have the same area of plates and same separation between them. X has air between the plates, while Y contains a dielectric medium of ε_r = 4.

(i) Calculate capacitance of each capacitor if the equivalent capacitance of the combination is 4 μF.

(ii) Calculate the potential difference between the plates X and Y.

(iii) Estimate the ratio of electrostatic energies stored in X and Y.

Meeta's father was driving her to school. At the traffic signal, she noticed that each traffic light was made of many tiny lights instead of a single bulb. When Meeta asked this question to her father, he explained the reason for this.

Answer the following questions based on above information:

(i) What were the values displayed by Meeta and her father?

(ii) What answer did Meeta's father give?

(iii) What are the tiny lights in traffic signals called and how do these operate?

How is a Zener diode fabricated?

Explain with the help of a diagram, how depletion region and potential barrier are formed in a junction diode.

If a small voltage is applied to a p-n junction diode, how will the barrier potential be affected when it is (i) forward biased

If a small voltage is applied to a p-n junction diode, how will the barrier potential be affected when it is(ii) reveres biased?

What should be the width of each slit to obtain 10 maxima of the double slit pattern within the central maximum of the single slit pattern, for green light of wavelength 500 nm, if the separation between two slits is 1 mm?

With what considerations in view, a photodiode is fabricated? State its working with the help of a suitable diagram.

Even though the current in the forward bias is known to be more than in the reverse bias, yet the photodiode works in reverse bias. What is the reason?

Write the expression, in a vector form, for the Lorentz magnetic force \[\vec{F}\] due to a charge moving with velocity \[\vec{V}\] in a magnetic field \[\vec{B}\]. What is the direction of the magnetic force? 

Derive the expression for the capacitance of a parallel plate capacitor having plate area A and plate separation d.

Using the necessary circuit diagrams, show how the V-I characteristics of a p-n junction are obtained in

Forward biasing

How are these characteristics made use of in rectification?

Using the necessary circuit diagrams, show how the V-I characteristics of a p-n junction are obtained in

Reverse biasing

How are these characteristics made use of in rectification?

A parallel plate capacitor with air between the plates has a capacitance of 8 pF (1pF = 10⁻¹² F). What will be the capacitance if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6?

What meaning would you give to the capacitance of a single conductor?

Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to (E_g)_C, (E_g)_Si and (E_g)_Ge. Which of the following statements is true?

A p-n photodiode is fabricated from a semiconductor with band gap of 2.8 eV. Can it detect a wavelength of 6000 nm?

State its any ‘two’ uses of photodiode.

Write the expression for the force `vecF` acting on a particle of mass m and charge q moving with velocity `vecV` in a magnetic field `vecB` , Under what conditions will it move in (i) a circular path and (ii) a helical path?