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Question

Q1 1.1. define the term “Q-factor” 1.2. define the term “bandwidth” Q2 2.1. a circuit having a resistance of 12 ohms, an indicator of 0,15H and a capacitor of 100uF in series, is connected across a 100V, 50Hz. Calculate a. the impedance b. the current c. the voltage R,L and C d. the phase difference between the current and the supply voltage. Also draw the phasor diagram of the circuit. 2.2. three branches having a resistance of 50ohms, an indicator of 0,15H and a capacitance of 100uF respectively are connected across a 100V, 50Hx supply. Calculate: a. the current in each branch b. the supply current c. the phase angle between the supply current and the supply voltage. Draw phasor diagram 2.3. a circuit consists of the following components: Z1=110-j21, 21 ohms Z2=150+j26, 41ohms Z3=100+j46, 31ohms If z1 and z2 are connected in parallel, and this combination is connected in series with z3 across a 240V, 50Hz supply. Calculate: a. the total impedance of the circuit to ensure maximum power transfer b. the current in different branches. Also draw the phasor diagram. Q3 3.1. use characteristic curves to indicate the operating principle of the following diodes: i. zener diode ii. tunnel diode iii. varactor diode 3.2. a diode works at a room temperature of 30 degrees Celsius with a forward voltage drop of 0,015V when a forward current of 20mA flows. Calculate the saturated reverse current. 3.3 . calculate the value of R5 needed in series with a 10V diode that has no load across it, if the source voltage is 15V and I2 is 200mA. Q4 4.1. calculate the current through 5 ohm resistor in the circuit shown in the figure below, wing Thavenins Theorem 4.2. calculate the current through 6 ohm using superposition’s theorem in the figures shown below.

Answer 1

1.1)

Q - factor (Quality factor): Q - factor of a resonant circuit is the measure of the "good ness" or "quality" of the circuit.

Q = X/R

Here, X is the capacitive reactance at resonance and R is the resistance .

Answer 2

(1.2)

Step 1:

Bandwidth is the difference between the upper and lower frequencies in a continuous set of frequencies.

It is typically measured in hertz , and may sometimes refer to pass band bandwidth, sometimes to base band bandwidth, depending on context.

Pass band bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a band pass filter , a communication channel  or a signal spectrum .

In the case of a low - pass filter  or base band signal , the bandwidth is equal to its upper cutoff frequency.

Where BW is bandwidth,

             f₂ is upper frequency,

             f₁ is lower frequency.

Answer 3

(4.2)

Step 1:

Find the current through 6 resistor :

Super Position Theorem :

Take one voltage source at a time and replace all other with short or internal resistance.

Indicate the direction of current in the above circuit.

Equivalent resistance :

9 resistor is in parallel with 6 resistor.

Resistance R_T is in series with 7 resistor.

Step 2:

Circuit current :

Current across each resistor :

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Contd...

Step 3:

Now Short circuit the other voltage source.

Indicate the direction of current in the above circuit.

Equivalent resistance :

7 resistor is in parallel with 6 resistor.

Resistance R_T is in series with 9 resistor.

Step 4:

Circuit current :

Current across each resistor :

 Step 5:

Current through 6 resistor =

     = Current produced by 6 resistor due to 5 V + Current produced by 6 resistor due to 10 V

     = 0.282 + 0.440

     = 0.722

Solution:

current flowing through the 6 resistor is 0.722 A.

Answer 4

Step 1:

(3.2)

The forward voltage drop is

The forward bias current is .

Room Temperature .

Absolute temperature .

The ideal law of diode : .

is the forward bias current.

is the reverse saturation current.

q  is the absolute value of the electron charge = 1.60217657 × 10^-19 c.

V_f  is the forward voltage drop.

k  is the Boltzmann's constant = 1.3806488 × 10^-23 m² kg s^-2 K^-1

T  is the absolute temperature.

 is the ideality factor.

Let us consider the diode to be made up of silicon then .

The reverse saturation current .

Solution:

The reverse saturation current .

Answer 5

2.3 (a)

Step 1:

Circuit having 3 impedance components and source.

.

z1 and z2 are connected in parallel.

This combination is connected in series with z3 across a 240V, 50Hz supply.

Draw a circuit with above specifications :

Find the total impedance of the circuit.

z1 and z2 are connected in parallel.

Step 2:

is in series with z3.

According to maximum power transfer theorem, the maximum power will transfer only if load impedance equals to source impedance .

So the impedance of the circuit that ensure maximum power transfer is .

Solution :

The impedance of the circuit that ensure maximum power transfer is .

Answer 6

2.3 (b)

Step 1:

The supply voltage is  240V, 50Hz.

The total circuit impedance is .

So the circuit is .

The circuit current is .

Also the current through the is .

The polar form of the is .

Phasor diagram of the :

Step 2:

Observe the circuit the voltage in parallel loop is same.

So .

Find the drop across .

Voltage in parallel loop is .

Find current in the :

The polar form of the is .

Phasor diagram of the :

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Step 3:

Find current in the :

The polar form of the is .

Phasor diagram of the :

Solution :

(i) Current through the is .

(ii) Current through the is .

(iii) Current through the is .