Rectifier is a device which is used for converting alternating current or voltage into direct current or voltage. Its working is based on the fact that the resistance of p-n junction becomes low when forward biased and becomes high when reverse biased. A half-wave rectifier uses only a single diode while a full wave rectifier uses two diodes as shown in figures (a) and (b) .

(i) If the rms value of sinusoidal input to a full wave rectifier is \(\frac{V_{0}}{\sqrt{2}}\) then the rms value of the rectifier's output is

\(\text { (a) } \frac{V_{0}}{\sqrt{2}}\)

\(\text { (b) } \frac{V_{0}^{2}}{\sqrt{2}}\)

\(\text { (c) } \frac{V_{0}^{2}}{2}\)

\(\text { (d) } \sqrt{2} V_{0}^{2}\)

(ii) In the-diagram, the input ac is actoss the terminals A and C. The output across Band D is

(a) same as the input

(b) half wave rectified

(c) zero

(d) full wave rectified

(iii) A bridge rectifier is shown in figure. Alternating input is given across A and C. If output is taken across BD, then it is

(a) zero

(b) same as input

(c) half wave rectified

(d) full wave rectified

(iv) A p-n junction (D) shown in the figure can act as a rectifier. An alternating current source (V) is connected in the circuit. The current (I) in the resistor(R) can be shown by

(v) With an ac input from 50 Hz power line, the ripple frequency is

(a) 50 Hz in the dc output of half wave as well as full wave rectifier

(b) 100 Hz in the de output of half wave as well as full wave rectifier

(c) 50 Hz in the de output of half wave and 100 Hz in dc output offull wave rectifier

(d) 100 Hz in the dc output of half wave and 50 Hz in the de output of full wave rectifier

From Bohr's atomic model, we know that the electrons have well defined energy levels in an isolated atom. But due to interatomic interactions in a crystal, the electrons of the outer shells are forced to have energies different from those in isolated atoms. Each energy level splits into a number of energy levels forming a continuous band.The gap between top of valence band and bottom of the conduction band in which no allowed energy levels for electrons can exist is called energy gap.

(i) In an insulator energy band gap is

(a) Eg = 0

(b) Eg< 3eV

(c) Eg > 3eV

(d) None of the above

(ii) In a semiconductor, separation between conduction and valence band is of the order of

(a) 0 eV

(b) 1 eV

(c) 10 eV

(d) 50 eV

(iii) Based on the band theory of conductors, insulators and semiconductors, the forbidden gap is smallest in

(a) conductors

(b) insulators

(c) semiconductors

(d) All of these

(iv) Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?

(a) The number of free electrons for conduction is significant only in Si and Ge but small in C.

(b) The number of free conduction electrons is significant in C but small in Si and Ge.

(c) The number of free conduction electrons is negligibly small in all the three.

(d) The number offree electrons for conduction is significant in all the three.

(v) Solids having highest energy level partially filled with electrons are

(a) semiconductor

(b) conductor

(c) insulator

(d) none of these

Light emitting diode is a photoelectric device which converts electrical energy into light energy. It is a heavily doped p-n junction diode which under forward biased emits spontaneous radiation. The general shape of the J- V characteristics of an LED is similar to that of a normal p-n junction diode, as shown. The barrier potentials are much higher and slightly different for each colour.

(i) The J- V characteristic of an LED is

(ii) The schematic symbol of light emitting diode is (LED)

(iii) An LED is constructed from a p-n junction based on a certain Ga-As-P semiconducting material whose energy gap is 1.9 eV. Identify the colour of the emitted light.

(a) Blue

(b) Red

(c) Violet

(d) Green

(iv) Which one of the following statement is not correct in the case of light emitting diodes?

(a) It is a heavily doped p-n junction.

(b) It emits light only when it is forward biased.

(c) It emits light only when it is reverse biased.

(d) The energy of the light emitted is less than the energy gap of the semiconductor used

(v) The energy of radiation emitted by LED is

(a) greater than the band gap of the semiconductor used

(b) always less than the band gap of the semiconductor used

(c) always equal to the band gap of the semiconductor used

(d) equal to or less than the band gap of the semiconductor used.