Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a voltage gain of 10 and the second has a voltage gain 20. If the input signal is 0.01 volt, Calculate the output ac signal.

In an n-type silicon, which of the following statement is true?
(a) Electrons are majority carriers and trivalent atoms are the dopants.
(b) Electrons are minority carriers and pentavalent atmos are the dopants.
(c) Holes are minority carriers and pentavalent atmos are the dopants.
(d) Holes are majority carriers and trivalent atmos are the dopants.

For the transistor action, which of the following statements are correct?
(a) Base, emitter and collector regions should have similar size and doping concentrations
(b) The base region must be very thin and lightly doped
(c) The emitter junction is forward biased and collector junction is reverse biased.
(d) Both the emitter junction as well as the collector junction are forward biased.

When an electronic field is applied across a semiconductor
(a) electrons move from lower energy level to lower energy level in the conduction band.
(b) electrons move from higher energy level to lower energy level in the conduction band.
(c) holes in the valence band move from higher energy level to lower energy level.
(d) holes in the valence band move from lower energy level to higher energy level 

To reduce the ripples in a rectifier circuit with capacitor filter
(a) \(R_{ L }\) should be increased
(b) input frequency should be decreased.
(c) input frequency should be increased.
(d) Capacitors with high capacitance should be used.

In the circuit \({ V }_{ s }=0.2\ V,{ V }_{ 0 }=-10V\). Find \({ V }_{ e }\), Gain \({ A }_{ u }=\frac { { V }_{ 0 } }{ V_{ c } } \) and \({ A }_{ 0 }=\frac { { V }_{ 0 } }{ V_{ s } } \)

A p-type semiconductor has acceptor energy level 53 meV above the valence band. Find the maximum wavelength of light that can create a hole. Use \(h=6.63\times 10^{ -34 }Js, \ c=3\times 10^{ 8 } \ ms^{ -1 }\)

On doping germanium with donor atoms of density \({ 10 }^{ 17 }\ cm^{ -3 }\), find its conductivity if mobility of electrons is \(3800\ cm^{ 2 }/V-s\) and intrinsic carrier concentration is \(2.5\times 10^{ 13 }\ cm^{ -3 }\) . Also, find the ratio of conductivity of doped germanium and pure germanium.

Write the two processes that take place in the formation of a p-n. junction. Explain with the help of a diagram, the formation of depletion region and barrier potential in a p-n. junction.

(i) Describe the working principle of a solar cell Mention three basic processes involved in the generation of emf.
(ii) Why are Si and GaAs preferred materials for solar cells.

Give reason for the following:
(i) High reverse voltage do not appear across a LED.
(ii) Sunlight is not always required for the working of a solar cell.
(iii) The electric field, of the junction of a Zener diode, is very high even for a small reverse bias voltage of about 5 V.

Three photo diodes D₁ , D₂ and D₃ are made of semiconductor having band gaps of 2.5 eV, 2eV and 3 eV respectively. Which one will be able to detect light of wavelength 600 \(\overset{o}{A}\)? 

The diode shown in the figure has a constant voltage drop of 0.5V at all currents and a maximum power rating of 100mW. What should be the value of resistance R connected in series, for maximum current.?