Class 12th

As the frequency of an AC circuit increases, the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit?

(a) Inductor and capacitor         

(b) Resistor and inductor

(c) Resistor and capacitor         

(d) Resistor, inductor and capacitor

The output of a step-down transformer is measured to be 24 V when connected to a 12 W light bulb. The value of the peak current is

(a) 1/ $\sqrt[]{2}$ A     

(b) $\sqrt[]{2}$ A         

(c) 2A

(d) 2 $\sqrt[]{2}$ A

An inductor of reactance 1 ? and a resistor of 2 ? are connected in series to the terminals of a 6 V (rms) AC source. The power dissipated in the circuit is

(a) 8 W               

(b) 12 W

(c) 14.4 W         

(d) 18 W

Which of the following combinations should be selected for better tuning of an L-C-R circuit used for communication?

(a) R = 20 ?, L = 1.5 H, C = 35μF

(b) R = 25 ?, L = 2.5 H, C = 45 μF

(c) R=15?, L = 3.5H, C = 30 μF

(d) R = 25 ?, L = 1.5 H, C = 45 μF

 To reduce the resonant frequency in an L-C-R series circuit with a generator

(a) The generator frequency should be reduced

(b) Another capacitor should be added in parallel to the first

(c) The iron core of the inductor should be removed

(d) Dielectric in the capacitor should be removed

When a voltage measuring device is connected to AC mains, the meter shows the steady input voltage of 220 V. This means

(a) Input voltage cannot be AC voltage, but a DC voltage

(b) Maximum input voltage is 220 V

(c) The meter reads not v but < v²> and is calibrated to read v²

(d) The pointer of the meter is stuck by some mechanical defect

An alternating current generator has an internal resistance R_gand an internal reactance X_gIt is used to supply power to a passive load consisting of a resistance R_g and a reactance X_L. For maximum power to be delivered from the generator to the load, the value of X_L is equal to

(a) Zero           

(b) X_g

(c) -X_g             

(d) R_g

If the rms current in a 50 Hz AC circuit is 5 A, the value of the current 1/300 s after its value becomes zero is

(a) 5 $\sqrt[]{2}\mathit{A}$   

(b) 5 $\frac{\sqrt[]{3}}{2}$ A           

(c) 5/6A         

(d) 5/ $\sqrt[]{2}$ A

For light diverging from a point source,
(a) The wavefront is spherical
(b) The intensity decreases in proportion to the distance squared
(c) The wavefront is parabolic
(d) The intensity at the wavefront does not depend on the distance

Consider the diffraction pattern for a small pinhole. As the size of the hole is increased
(a) The size decreases     

(b) The intensity increases
(c) The size increases       

(d) The intensity decreases