36 questions and answers
A coil of resistance 10 Ω and inductance 0.02 Hs connected in series with another coil of resistance 6 Ω and inductance 15 mH across a 230 V, 50 Hz supply. calculate
The circuit diagram of question 6(b) is given in Fig. 27. Total impedance for coil 1 is \(Z_1=\left(10+j\times2\pi\times50\times0.02\right)=(10+j6.282)\ \mathrm{\Omega}\)
A flux of 0.0006Wb is required in the air – gap of an iron ring of cross – section 5.0 cm2and mean length 2.7 m with an air – gap of 4.5 mm. Determine the ampere turns required. Six H values and corresponding B values are noted from the magnetization curve of iron and given below.
H(At/m) |
200 |
400 |
500 |
600 |
800 |
1000 |
B(Wb/m2) |
0.4 |
0.8 |
1.0 |
1.09 |
1.17 |
1.19 |
Given that, Flux=0.0006 Wb Cross section area \(A=5\ {cm}^2=5\times{10}^{-4}m^2\)
A 20 Ω resistor, a choke coil having some inductance and some resistance and a capacitor are connected in series across a 25 V variable frequency source. When frequency is 400 Hz, the current is maximum and its value is 0.5 Amp and the potential difference across the capacitor is 150 V. Calculate the resistance and the inductance of the chokes coil and the capacitance of the capacitor.
The total impedance of the circuit is \(R_{eq}=20+R+j\omega L-\frac{1}{\omega C}\) The maximum current is following through the circuit at the time of resonance. For the resonance \(X_L\) and \(X_C\) is same.
State Ampere’s Circular law.
Ampere’s circular law states that the line integral of the tangential component of the magnetic field around a closed path is equal to the current enclosed by the path.
Two coils have self inductance \(L_{1}\) and \(L_{2}\) and mutual inductance between them is M. Derive a mathematical expression for co – efficient of coupling (k) for these coils. Find an expression for the energy stored in a magnetic field.
The above inductor having inductance L is connected to the bettery through key K. In this case inducted e.m.f is given by \(e=-L\frac{dL}{dt}\) …(1)
State and explain Biot – Savart law.
This law was deduced from a number of experiments on the effect of current carrying conductor on permanent magnets such as the compass needle experiment of oersted.
A ring having a mean diameter of 21 cm and a cross – section of 10 cm2 is made of two semicircular section of cost iron and cost steel respectively with each joint having reluctance equal to air gap of 0.2 mm as shown in figure. Determine the ampere turns required to produce a flux of 0.8 mWb. The relative permeability of cost iron and cost steel are 166 and 800 respectively. Neglect fringing and leakage effects.
The ring consists of two parallel magnetic circuits of semiconductor cross sections having reluctances \(R_C\) and \(R_S\) corresponding to cost iron and cost steel respectively. The reluctance of the joint,
Prove that current is purely resistive circuit is in phase with applied A.C. voltage and current purely capacitive circuit leads applied voltage by 900 and draw their waveform.
A pure resistive circuit is shown in Fig. 12(a) contain a pure resistance R connected across an AC sinusoidal voltage source. The instantaneous value of an alternating source voltage is given by
Derive the expression of quality factor of series R-L-C circuit at resonance.
The quality factor is , in general, defined as the ratio of resonant frequency to bandwidth. It is given by
A two element series circuit consumes 700 V of power and has power factor of 0.707 leading when energized by a voltage source of waveform \(v=141\sin\left(314t+30^{\circ}\right)\). Find out the circuit element.
The power dissipated by the coil is \(P_C=I_{rms}V_{rms}\ cos\ \phi\) For this problem \(V_{rms}=\frac{V_{peak}}{\sqrt2}=\frac{141}{\sqrt2}=100\ V\)
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