Science (English Medium) Class 12 - CBSE Important Questions for Physics

 Identify the equivalent gate for the following circuit and write its truth table.

Write two characteristic features to distinguish between n-type and p-type semiconductors ?

How does a light emitting diode (LED) work? Give two advantages of LED’s over the conventional incandescent lamps.

Draw the circuit for studying the input and output characteristics of and transistor in CE configuration. Show, how, from the output characteristics, the information about the current amplification factor (β_ac) can obtained.

Draw a plot of the transfer characteristics (V₀ versus V_i) for a base-biased transistor in CE configuration. Show for which regions in the plot, the transistor can operate as a switch ?

Why is a zener diode considered as a special purpose semiconductor diode?

Draw the I − V characteristics of zener diode and explain briefly how reverse current suddenly increase at the breakdown voltage.

Describe briefly with the help of a circuit diagram how a zener diode works to obtain a constant dc voltage from the unregulated dc output of a rectifier ?

The output of an OR gate is connected to both the inputs of a NAND gate Draw the logic circuit of this combinaion of getes and write its truth table.

(i) Write the truth tables of the logic gates marked P and Q in the given circuit.
(ii) Write the truth table for the circuit. 

Why are NOR gates considered as universal gates?

Explain how a potential barrier is developed in a p-n junction diode.

Draw the circuit arrangement for studying the V-I characteristics of a p-n junction diode in reverse bias. Plot the V-I characteristics in this case.

Draw the V-I characteristics of an LED. State two advantages of LED lamps over convertional  incandescent lamps. 

Answer the following question.
Three photodiodes D1, D2, and D3 are made of semiconductors having band gaps of 2.5 eV, 2 eV, and 3 eV respectively. Which of them will not be able to detect light of wavelength 600 nm? 

Answer the following question.
Why photodiodes are required to operate in reverse bias? Explain.

Answer the following question.
Describe briefly the functions of the three segments of the n-p-n transistor.

The wavelength and intensity of light emitted by a LED depend upon ______.

The ability of a junction diode to ______ an alternating voltage is based on the fact that it allows current to pass only when it is forward biased.

Explain the three processes involved in the working of a solar cell.