undefined | unit 2 electrostatics and ac fundamentals 12

Basic Electrical Engineering

Unit 2 Electrostatics(A)

Derive an expression for capacitance of a simple parallel plate capacitor. (6 Marks)

Obtain an expression for energy stored in capacitor. (6M)

Sketch graph of charging voltage , charging current , discharging voltage and discharging current of capacitor and also write there expressions. (6 Marks)

80µF capacitor in series with a 1000 ohm resistor is connected suddenly across a 110 V supply. Find: 1) Initial value of current 2) Time constant 3) Equation of current 4) Value of current at t=0.08 sec (6M)

A parallel plate capacitor has plates 0.1 cm apart, a plate area of 100 cm² and a dielectric with relative permittivity of 4. Determine the electric flux, electric flux density, electric field intensity, voltage between the plates and value of capacitance. (6M)

Two parallel plates measuring 1m*2m & separated 10cm are charged y transferring 10-6 coulombs’ from one plate to other. The permittivity of the oil between the plates is 2. Calculate:

1) Capacitance 2) Potential difference
3) Electric field intensity4) Electric flux density(6M)

A capacitor having capacitance of 4 µF is connected in series with a resistance of 1 M across 200 V d.c. supply. Calculate : (i) The time constant, (ii) The initial charging current, (iii) The time taken by capacitor to raise upto 160 V. (6M)

8. A capacitor of 2 µF capacitance charged to potential difference of 200 V is discharged through a resistor of 2M.Calculate : (i) The initial value of discharging current, (ii) its value after 4 sec (iii)initial rate of decay of the capacitor voltage. (6M) A.C. Fundamentals

Prove that rms value of the sinusoidal alternating current is 0.707 times its maximum value. (6M)

2. Define average value of alternating quantity and derive its expression for sinusoidal current. (6M)

3. 5. A 50Hz sinusoidal voltage has rms value of 200 V. At t =0, the instantaneous value is positive and half of its maximum value. Write down the expression for voltage and sketch the wave form. (6M) 4. The mathematical expression for the instantaneous value of an alternating current is i=7.071 sin(157.08t- π/4)Amps. Find its effective value, periodic time ,and the instant at which it reaches its positive maximum value. Sketch the waveform from t=0 over one complete cycle. (6M) 5. An alternating current varying sinusoidally at 50 Hz has an rms value of 10 amps. Write down equation for instantanous value of current at, i)0.0025 sec after passing through positive maximum value. ii) 0.0075 sec after passing through zero value and increasing negatively. (6M) 6. The mathematical expression for the instantaneous value of an alternating current is i=7.071 sin(157.08t- π/4)Amps. Find its effective value, periodic time ,and the instant at which it reaches its positive maximum value. Sketch the waveform from t=0 over one complete cycle. (6M) 7. Calculate Average value, Effective value, Peak factor Form factor for the output of half wave rectifier if its peak vale is 100V(6M) 8. The Instantaneous current is given by, i=6.661sin(157.08t-π/4). Find its effective value, periodic time & the instant at which it reaches its positive maximum value. Sketch the waveform from t=0 over one complete one cycle.

At t=0,The value of 60Hz Sinusoidal current is +5 Ampere & increases in magnitude further. Its r.m.s. value is 8A.

1)Write expression for its instantaneous value.

Find current at t=0.010sec & t=0.02sec.

Sketch the waveform indicating these values. (6M)

The Instantaneous current is given by, i=7.071sin(157.08t-π/4). Find its effective value, periodic time & the instant at which it reaches its positive maximum value. Sketch the waveform from t=0 over one complete one cycle. (6M)

The branch currents are given of parallel circuit as, i1=5sin346t, i2 = 10sin(346t+π/4) i3=7.5 sin (346t+π/2) , i4=8sin(346t-π/3). Find resultant current & write expression for the same. (6M)

At the instant t=0,the instantaneous value of a 50Hz sinusoidal current 5A and increases in magnitude further. Its rms value is 10A.i)Write the expression for its instantaneous value. ii)Find the current at t=0.01 s and t=0.015s.iii)Sketch the waveform indicating these values. (6M)

An alternating current is given by; i =14.14sin 377t Find i) RMS value of current, ii) instantaneous value of current when t=3msec, iii) time taken by current to reach 10A for first time after passing through zero and increasing positively. iv) draw waveform if current is leading with an angle of 50˚. (6M)

Sketch phasor of currents and find its RMS value and average value for equations; i1 = 15 sin (314.159 t), i2 = 10 sin (314.159 t –π/2). Find frequency. (3M)

Three voltages represented by, e1 = 20sinωt; e2 = 30sin(ωt - π/4); e3= 40cos(ωt + π/6) are voltages across three loads connected in series. Find its supply voltage (resultant voltage) and express it in form of, e = Em sin(ωt± θ). (3M)

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