Tiêu đề 07. ALTERNATING CURRENT.pdf ✅

07. ALTERNATING CURRENT NEET PREPARATION (MEDIUM PHYSICS PAPER) Date: March 12, 2025 Dura on: 1:00:00 Total Marks: 180 INSTRUCTIONS INSTRUCTIONS PHYSICS 1. In a step-up transformer, the ratio of turns of the primary and the secondary is . If the input voltage is and the current through the load is , then the current in the primary coil is (1) (2) (3) (4) 2. A group of electric lamps having a total power rating of 1000 watt is supplied by an voltage Then the rms value of the circuit current is[ Here ] (1) (2) (3) (4) 3. In parallel resonance circuit, choose the wrong statement. (1) At resonance, cur- rent is minimum. (2) At resonance, im- pedance is maximum. (3) Resonance oc- curs when inductive and capcitive reac- tance is same. (4) At resonance, res- onate frequency . 4. In an series circuit, . If applied voltage in the circuit is then impedance of the circuit (in ) will be (1) 2 (2) 3 (3) (4) 5. Reactance of a capacitor of capacitance for ac frequency is . The value is: (1) (2) (3) (4) 6. The power factor of an - circuit is . If the frequency of is doubled, then what will be the power factor? (1) (2) (3) (4) 7. The r.m.s. current in an circuit is 2 . If the wattless current be , what is the power factor? (1) (2) (3) (4) 8. Assertion : By only knowing the power factor for a given LCR circuit it is not possible to tell whether the applied alternating e.m.f. leads or lags the cur‐ rent. Reason : (1) Both Assertion and Reason are cor- rect and Reason is the correct explana- tion of the Assertion. (2) Both Assertion and Reason are cor- rect but Reason is not the correct explana- tion of the Assertion. (3) Assertion is cor- rect but Reason is incorrect. (4) Assertion is incor- rect but reason is correct. 9. In series circuit, the capacitance is changed from to To keep the resonance frequency unchanged, the new inductance should be (1) reduced by (2) reduced by 1 : 25 230 V 2A 50 A 25 A 12.5 A 6.25 A AC E = 200 sin(3 10t + 60 ∘ ). i = io sin 310t 20√2A 10A 20A 10√2A LC = √LC L − C − R R = √5 Ω, XL = 9 Ω, XC = 7 Ω 50 V ohm 2√5 3√5 CμF Hz 400 π 25 Ω C 50 μF 25 μF 100 μF 75 μF R L 1 √2 AC 1 √3 1 √5 1 √7 1 √11 AC A √3A 1 √2 1 √3 1 3 1 2 cos θ = cos(−θ) LCR C 4 C. L 1 4 L 3 4

23. The frequency of an alternating current is 50 , What is the minimum time taken by current to reach its peak value from value ? (1) (2) (3) (4) 24. If reading of an ammeter is 20 , then the peak value of current is: (1) (2) (3) (4) 25. A series circuit is connected across an ac source .Current from the supply is .What is the average power dissipated? (in watt) (1) (2) (3) (4) 26. To reduce the resonant frequency in an series circuit with a generator (1) The iron core of the inductor should be removed (2) Dielectric in the capacitor should be removed (3) The generator fre- quency should be reduced (4) Another capacitor should be added in parallel to the first 27. Assertion : We use a thick wire in the secondary coil of a step down transformer to reduce the production of heat. Reason : When the plane of the armature is parallel to the line of force of magnetic field, the magnitude of induced is maximum. (1) Both Assertion and Reason are cor- rect and Reason is the correct explana- tion of the Assertion. (2) Both Assertion and Reason are cor- rect but Reason is not the correct explana- tion of the Assertion. (3) Assertion is cor- rect but Reason is incorrect. (4) Assertion is incor- rect but reason is correct. 28. An alternating current of rms value is passed through a resistor. The maximum po‐ tential difference across the resistor is (1) (2) (3) (4) None of these 29. If the reading of voltmeter is 40 , what is the reading of voltmeter ? (1) (2) (3) (4) 30. Match the Column I and Column II Choose the correct answer from the options given below : (1) A – S, B – P, C – R, D – Q (2) A – P, B – S, C – Q, D – R (3) A – S, B – P, C – Q, D – R (4) A – P, B – S, C – R, D – Q 31. A choke coil has negligible resistance. The al‐ ternating potential drop across it is and the current is The power consumed is (1) (2) (3) Zero (4) 32. Assertion : When capacitive reactance is smaller than the in‐ ductive reactance in series circuit, e.m.f. leads the current. Reason : The phase angle between the applied and alternating current in the circuit is zero in that case. Hz rms 0.2 s 5 × 10 −3 s 10 × 10 −3 s 2.5 × 10 −3 s A A 20 √2 A 5 √2 20√2A 20√2 LCR E = 10 sin[100πt + ] π 6 I = 2 sin[100πt + ] π 12 5 8 20 √2 5√2 L − C − R e. m. f 10 A 12Ω 20 V 90 V 169.68 V V1 V V2 40 V 20 V 30 V 10 V 220 volts 5 mA. 220 × W 5 1000 W 220 5 2.20 × 5 W LCR e. m. f L
(1) Both Assertion and Reason are cor- rect and Reason is the correct explana- tion of the Assertion. (2) Both Assertion and Reason are cor- rect but Reason is not the correct explana- tion of the Assertion. (3) Assertion is cor- rect but Reason is incorrect. (4) Assertion is incor- rect but reason is correct. 33. A resistor and an inductor are connected to an ac supply of and . The current in the circuit is . If the power consumed in the cir‐ cuit is , then the resistance in the circuit is (1) (2) (3) (4) 34. A coil of self-inductance is connected in se‐ ries with a bulb and an source. Brightness of the bulb decreases when (1) Number of turns in the coil is reduced (2) A capacitance of reactance is induced in the same circuit (3) Frequency of the source is decreased (4) An iron rod is in- serted in the coil 35. In a circuit connected in series with an alternating voltage source of frequency . The current leads the voltage by . The value of is (1) (2) (3) (4) 36. An alternating voltage volt is connected to capacitor through ammeter. The reading of ammeter is (1) (2) (3) (4) 37. The value of an of 50 is 10 . The time taken by an alternating current in reaching from zero to maximum value or the peak value will be (1) (2) (3) (4) 38. Statement A : The power in an ac circuit is minimum if the cir‐ cuit has only a resistor. Statement B : Power of a circuit is independent of the phase angle. (1) Statement A is correct but Statement B is incorrect. (2) Statement A is in- correct but Statement B is correct. (3) Both Statements are correct. (4) Both Statements are incorrect. 39. The vector diagram of current and voltage for a circuit is given. The components of the circuit will be (1) (2) (3) or (4) None of these 40. The turns ratio of a transformer is given as 2 : 3. If the current through the primary coil is 3 , thus calculate the current through load resistance. (1) (2) (3) (4) 41. Read the Statement - A and Statement - B care‐ fully to mark the correct options given below: Statement A : When the frequency of an a.c. source in a series circuit increases, the current in the circuit first increases, attains a maximum value and then decreases. Statement B : In a series circuit, the value of power fac‐ tor at resonance is one. (1) Statement A is in- correct but Statement B is correct. (2) Both Statement A and Statement B are correct. (3) Statement A is correct but Statement B is incorrect. (4) Both Statement A and Statement B are incorrect. 42. Assertion : An electric heater is heated first by direct and then by alternating currents. For both the cur‐ rents, the potential difference across the ends of the heater is the same. The rate of production of heat will be different in two cases. Reason : The resistance of a coil in alternating curent will be more than the resistance of a coil in direct current. 120V 50Hz 3A 108W 360Ω 40Ω 12Ω √(52 × 28)Ω L B AC XC = XL AC L, C, R f 45 ∘ C 1 2πf(2πfL+R) 1 πf(2πfL−R) 1 2πf(2πfL−R) 1 πf(2πfL+R) e = 200√2 sin(100t) 1μF AC 5mA 10mA 15mA 20mA rms ac Hz A 5 × 10 −3 s and 14.14A 1 × 10 −2s and 7.07A 2 × 10 −2s and 14.14A 5 × 10 −3s and 7.07A LCR LR LCR LR A 1 A 4.5 A 2 A 1.5 A LCR LCR