৪৯তম বিসিএস ⎯ তথ্য ও যোগাযোগ প্রযুক্তি (EEE) [ ৮৯২]

A low-pass filter (LPF) attenuates frequencies above its cutoff frequency while passing lower frequencies unchanged

In an RC high-pass filter, the capacitor blocks low frequencies, while higher frequencies pass through to the resistor. Thus, the output voltage is measured across the resistor.  

Band-stop filters attenuate a narrow frequency band  while passing others.  

Higher Q means a narrower bandwidth  

At resonance, XL=XC, so the net reactance is zero, making impedance purely resistive (Z=R), which is the minimum possible.

Since XL=XC, the circuit is purely resistive, so voltage and current are in phase.

V_L=IX_L  and V_C =IX_C  are equal in magnitude but cancel each other due to a 180° phase difference.

At higher frequencies, X_L>X_C making the circuit inductive.

Q=XL/R so increasing R reduces Q.

 The reactive branch currents cancel, minimizing the total line current.

It stores energy alternately between L and C, resembling a tank.

Half-power points occur at 1/√2 of peak current/voltage.

Both magnitude and phase

Power is nonlinear (P=I²R or V²/R), so superposition doesn’t apply.

Resistive loads simplify to matching resistances.

Dependent sources must remain active during superposition analysis as they rely on other circuit variables.

Y_N = I_sc/V_oc = (2-j3)/(10+j15) = 0.15+j0.1S 

P=VI×PF=120×10×0.8=960WP=VI×PF=120×10×0.8=960W.

θ=cos⁡−1(P/S)=cos⁡−1(0.6)=53.13°

P=Scos⁡(45°)=70.7W,  Q=Ssin⁡(45°)=70.7VAR

S=√(P² +Q² )=1000VA, PF=P∣S∣=0.8, Since Q>0Q>0, the PF is lagging (inductive load).

If one wattmeter reads zero, the phase angle ϕ=60°
Power factor cos⁡ϕ=cos⁡60°=0.5
Since the reading becomes zero due to a lagging phase angle, the power factor is 0.5 lagging.

one wattmeter reads positive and the other negative with the same magnitude.

Q=√3(W1−W2)=500√3

Swapping Vab and Vcb causes the readings to interchange 

Unbalanced loads cause voltage fluctuations.  Requires a tertiary winding or grounding for practical use.

I_L=√3I_p

A generator having two or more electrical windings which are separated by equal electrical angle generates a polyphase electrical system.

Line voltage, VL = 230 V
Power Factor, cosφ = 0.5
Power consumed = P = 1800 Watts = √3 VL x IL x cosφ
 line current, IL = 9 Amperes
Since it is a star connection, phase current = line current = 9 Amperes
Phase Voltage, Vph = VL/√3 = 132.8 Volts
Phase Impedance, Zph = Vph/Iph = 14.7 Ohms

for sine or cosine function, over one period of time , average value is zero