Test: Basic Electronics- 3 - Electrical Engineering (EE) MCQ

Mobility of electrons and holes depends on their effective masses. Effective mass of electrons is less than that of holes hence electrons have higher mobility than holes.

For both G_e & S_i μ_e > 2μ_h

Hence option (b) is correct.

In a p-n Junction when no bias voltage is applied, the net current is zero.

Hence the drift and diffusion components of the hole and electron currents must sum to zero.

From the definition of fermi level, the fermi level is energy state having probability ‘1/2’ of being occupied by an electron.

LASER stands for Light Amplification by Stimulated Emission of Radiation. These are based on the principle of population inversion at a junction as explained in below figure

The frequency Response is shown

Bandpass filters at ω₀ = 1/RC

During forward Bias, the diffusion capacitance is the dominant capacitance.

τ = mean lifetime of minority carriers

I_f = forward current

As forward current Increase exponentially,

The junction capacitance increases exponentially on forward bias.

LED works on the principle of electroluminescence which is emission of light under influence of electric field.

For a BJT operating in active mode, the base current (I_b) and collector current (I_C) are related as I_c = β I_b where β is the current gain.

At saturation the voltage across collector – emitter junction (V_CE) is constant (∼ 0.2V) and collector current is independent of base current.

Commutation in a rectifier is the process of transfer of current from one device (diode or thyristor) to the other in a rectifier. The device from which the current is transferred is called the outgoing device and the device to which the current is transferred is called the incoming device. The incoming device turns on at the beginning of commutation while the outgoing device turns off at the end of commutation.

Here, commutation of diodes refers to transferring energy from rectifier diode to freewheeling diode. Freewheeling diode is used to reduce the harmonics and also suppress the voltage spikes occur in inductive load.

The frequency response of LPF is shown

From the frequency response it is clear that the gain of low pass filter decreases form finite value to zero as frequency is increased from 0 to ∞

The current gain β is defined as 

At higher temperatures the thermal injection increases the collector current & hence β increases.

The h-parameters model doesn’t take into account junction capacitance which are significant at high frequencies. The h-parameter model is valid for signals with V_be < 10 mV. Hence h-parameter model is suitable for low frequencies & small signals

The leakage current in a transistor mainly depends on temperature and doubles for every 10°C rise in temperature. This leakage current dependence on temperature is responsible for thermal run-away in transistors.

In pnp transistor, the base is n-type semiconductor i.e. it is doped with electrons. The width of the base region is kept small/thin to allow maximum carriers from emitter to pass through base to collector without much recombination

The Q-point in the Transistor is established for faithful Amplification in middle of DC-load line. The Q-point is established using DC voltage & resistance without any application of AC signal.

The order of width is

w_collector > w_emitter > w_Base

The order of doping is

n_emitter > n_collector > n_base

Tuned amplifiers are employed for the purpose of selecting a particular frequency among set of available frequencies. Hence they are employed in radio receives.

The overdrive voltage is defined as the voltage between transistor gate and source (V_GS) in excess of the threshold voltage (V_T) ie V_gs - V_t

For N-Mos to function as a resistor, it should be operated in linear region. I.e. V_DS < V_gs – V_t

For using N-Mos as an amplifier, it should be operated in saturation region. I.e. V_DS ≥ V_gs – V_t