Tiêu đề ALTERNATING CURRENT (AC).pdf ✅

NEET : Physics [ 224 ] www.allendigital.in  Digital PEAK, AVERAGE AND RMS VALUE 1. What is the r.m.s. value of an alternating current which when passed through a resistor produces heat which is thrice of that produced by a direct current of 2 amperes in the same resistor :- (1) 6 amp (2) 2 amp (3) 3.46 amp (4) 0.66 amp 2. The peak value of an alternating e.m.f. which is given by E = E0 cost is 10 volts and its frequency is 50 Hz. At time t = 1 600 s, the instantaneous e.m.f. is (1) 10 V (2) 5 3 V (3) 5 V (4) 1V 3. The phase difference between current and voltage in an AC circuit is 4  radian. If the frequency of AC is 50 Hz, then the phase difference is equivalent to the time difference:- (1) 0.78 s (2) 15.7 ms (3) 2.5 s (4) 2.5 ms 4. A current in circuit is given by i = 3 + 4 sin t. Then the effective value of current is : (1) 5 (2) 7 (3) 17 (4) 10 5. Incorrect statement are : (a) A.C. meters can measure D.C also (b) If A.C. meter measures D.C. there scale must be linear and uniform (c) A.C. and D.C. meters are based on heating effect of current (d) A.C. meter reads rms value of current (1) a, b (2) b, c (3) c, d (4) d, a 6. The r.m.s. value of current for a variable current i = i1 cos t + i2 sin t :– (1) 1 2 1 (i i ) 2 + (2) 2 1 2 1 (i i ) 2 + (3) 2 2 1 2 1 2 1 (i i ) 2 + (4) 2 2 1/2 1 2 1 (i i ) 2 + 7. The relation between an A.C. voltage source and time in SI units is : V = 120 sin (100 t) cos (100 t) volt value of peak voltage and frequency will be respectively :– (1) 120 volt and 100 Hz (2) 120 2 volt and 100 Hz (3) 60 volt and 200 Hz (4) 60 volt and 100 Hz 8. If an A.C. main supply is given to be 220 V. What would be the average e.m.f. during a positive half cycle :- (1) 198 V (2) 386 V (3) 256 V (4) None of these 9. The hot wire ammeter measures :- (1) D.C. current (2) A.C. current (3) None of above (4) both (1) & (2) 10. Frequency of A.C. in India is – (1) 45 Hz (2) 60 Hz (3) 50 Hz (4) None of the above 11. For an alternating current I = I0 cos t, the rms value and peak value of current is :- (1) I0 , 0 I 2 (2) 0 I 2 , I0 (3) I0 , 0 I 2 (4) 2I0 , 0 I 2 12. If a step-up transformer have turn ratio 5, frequency 50 Hz root mean square value of potential difference on primary 100 volts and the resistance of the secondary winding is 500  then the peak value of voltage in secondary winding will be (the efficiency of the transformer is hundred percent) (1) 500 2 (2) 10 2 (3) 50 2 (4) 20 2 Exercise - I

NEET : Physics [ 226 ] www.allendigital.in  Digital 22. A bulb and a capacitor are connected in series to a source of alternating current. If its frequency is increased, while keeping the voltage of the source constant, then (1) Bulb will give more intense light. (2) Bulb will give less intense light. (3) Bulb will give light of same intensity as before (4) Bulb will stop radiating light. 23. In an A.C. circuit resistance and inductance are connected in series. The potential and current in inductance is: (1) V0 sin t, V0 L sint (2) V0 sin t, V0 L sin(t + /2) (3) V0 sin (t+ /2), V0 L sint (4) V0 sin(t + /2), V0 L sin(t–/2) 24. An a.c. source of voltage V and of frequency 50 Hz is connected to an inductor of 2H and negligible resistance. A current of r.m.s value I flows in the coil. When the frequency of the voltage is changed to 400 Hz keeping the magnitude of V the same, the current is now :- (1) 8I in phase with V (2) 4I and leading by 90° from V (3) I 4 and lagging by 90° from V (4) I 8 and lagging by 90° from V 25. A capacitor of capacity C is connected in A.C. circuit. The applied emf is V=V0 sint, then the current is : (1) I = V0 L sint (2) I = V0 L sin(t + /2) (3) I = V0 C sint (4) I = V0 C sin (t + /2) 26. The impedence of a circuit, when a resistance R and an inductor of inductance L are connected in series in an A.C. circuit of frequency (f) is :- (1) 2 R 4 fL +  (2) 2 2 2 R 4 f L +  (3) 2 2 2 2 R 4 f L +  (4) 2 2 2 2 R 2 f L +  27. A capacitor of capacity C and reactance X if capacitance and frequency become double then reactance will be :– (1) 4X (2) X 2 (3) X 4 (4) 2X 28. The coil of choke in a circuit : (1) increases the current (2) controls the current (3) has high resistance to d.c. circuit (4) does not change the current 29. The inductive reactance of an inductive coil with 1  henry and 50 Hz :– (1) 50  ohm (2) 50  ohm (3) 100 ohm (4) 50 ohm 30. In the L–R circuit R = 10 and L = 2H. If 120V, 60Hz alternating voltage is applied then the flowing current in this circuit will be :- (1) 0.32 A (2) 0.16 A (3) 0.48 A (4) 0.80 A 31. An inductance of 0.4 Henry and a resistance of 100 ohm are connected to a A.C. voltage source of 220 V and 50 Hz. Then find out the phase difference between the voltage and current flowing in the circuit : (1) tan–1 (2.25 ) (2) tan–1 (0.4 ) (3) tan–1 (1.5 ) (4) tan–1 (0.5 ) 32. A capacitor of capacitance 100 F & a resistance of 100 is connected in series with AC supply of 220V, 50Hz. The current leads the voltage by (1) tan–1 1 2        (2) tan–1   1      (3) tan–1   2      (4) tan–1   4     