Two cables of copper are of equal lengths. One of them has a single wire of area of cross- section A, while other has 10 wires of cross-sectional area A/10 each. Give their suitability for transporting A.C. and D.C.
(a) only multiple strands for A.C., either for D.C.
(b) only multiple strands for A.C., only single strand for D.C.
(c) only single strand for D.C., either for A.C.
(d) only single strand for A.C., either for D.C.
(a) only multiple strands for A.C., either for D.C.
(b) only multiple strands for A.C., only single strand for D.C.
(c) only single strand for D.C., either for A.C.
(d) only single strand for A.C., either for D.C.
(a) only multiple strands for A.C., either for D.C.
A source of ac voltage V = V₀ sin ωt is connected to a series combination of a resistor ‘R’ and a capacitor ‘C’. Draw the phasor diagram and use it to obtain the expression for
(i) impedance of the circuit and
(ii) phase angle.
A transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil respectively are
(a) 300 V, 15 A
(b) 450 V, 15 A
(c) 450 V, 13.5 A
(d) 600 V, 5 A
The core of a transformer is laminated because
(a) ratio of voltage in primary and secondary may be increased
(b) energy losses due to eddy currents may be minimized
(c) the weight of the transformer may be reduced
(d) rusting of the core may be prevented
An AC voltage source of variable angular frequency ω and fixed amplitude V connected in series with a capacitance C and an electric bulb of resistance R (inductance zero). When ω is increased
(a) The bulb glows dimmer
(b) The bulb glows brighter
(c) Net impedance of circuit is unchanged
(d) Total impedance of the circuit increases
An inductor of 200 mH, capacitor of 400 µF and a resistor of 10 Ω are connected in series to ac source of 50 V of variable frequency. Calculate the
(a) angular frequency at which maximum power dissipation occurs in the circuit and the corresponding value of the effective current, and
(b) value of Q-factor in the circuit.
In the following circuit, calculate (i) the capacitance of the capacitor, if the power factor of the circuit is unity, (ii) the Q-factor of this circuit. What is the significance of the Q-factor in ac circuit ? Given the angular frequency of the ac source to be 100rad/s. Calculate the average power dissipated in the circuit.
A sinusoidal voltage of peak value 10 V is applied to a series LCR circuit in which resistance,capacitance and inductance have values of 10 Ω,1 µF and 1 H respectively. Find
(i) the peak voltage across the inductor at resonance
(ii) quality factor of the circuit.
A capacitor of capacity C has reactance X. If capacitance and frequency become double then reactance will be
(a) 4X
(b) X/2
(c) X/4
(d) 2X
What happens if one of the slits, say S1 in Young’s double, slit experiment-is covered with a glass plate which absorbs half the intensity of light from it?
(a) The bright fringes become less-bright and the dark fringes have a finite light intensity.
(b) The bright fringes become brighter and the dark fringes become darker.
(c) The fringe width decreases.
(d) No fringes will be observed.
A wavefront of a wave has direction with wave motion
(A) Parallel
(B) Perpendicular
(C) opposite
(D) at any angle θ
The colours of a soap bubble seen in sunlight is due to ......... And colour due to a prism appears due to .............
Choose the right answers respectively
(A) Interference of light; refraction of light
(B) Dispersion of light; total internal reflection of light
(C) Interference of light; polarization of light
(D) Interference of light; dispersion of light
A dielectric induces....... in an external electric field which decreases the net electric field.
(a) current
(b) dipole moment
(c) magnetic field
(d) polarisation
Bending of Light phenomena is shown by
(a) Polarization
(b) Diffraction
(c) Interference
(d) Dispersion
A resistance of R Ω draws current from a potentiometer. The potentiometer has a total resistance \(R_0\) Ω as shown in the Fig below. A voltage V is supplied to the potentiometer. Derive an expression for the voltage across R when the sliding contact is in the middle of the potentiometer.