Tiêu đề 20 JUNE PAPER.pdf ✅

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PHYSICS 1. The self inductance of the motor of an electric fan is 10H. In order of impart maximum power at 50 Hz, it should be connected to a capacitance of (A) 1 μF (B) 2 μF (C) 4 μF (D) 8 μF 2. 200 V ac source is fed to series LCR circuit having XL = 50Ω, XC = 50Ω, R = 25Ω. Potential drop across the inductor is (A) 100 V (B) 200 V (C) 400 V (D) 10 V 3. At what angular frequency the inductive reactance of 2 H inductance will be equal to the capacitive reactance of a capacitor of 2μF ? (A) 5 rad/s (B) 50 rad/s (C) 500 rad/s (D) 5000 rad/s 4. A resistance of 5Ω and an inductance of 50 mH are connected in series with an a.c. I = 100 sin (100 t). What is the phase difference between the instantaneous current and voltage ? (A) 30° (B) 45° (C) 60° (D) 90° 5. In the given circuit, bulb will become suddenly bright, if (A) Switch is closed or opened (B) Switch is closed (C) Switch if opened (D) None of these 6. Figure shows an L-R circuit. When the switch S is closed, the current through resistor R1, R2 and R3 and I1, I2 and I3 respectively. The value of I1, I2 and I3 at t = 0 s is (A) I1 = I2 = I3 = 0 (B) 1 1 E I R = , I2 = I3 = 0 (C) I1 = 0, 2 1 E I R = , 3 3 E I R = (D) 1 2 3 1 2 1 3 3 , , E E E I I I R R L R L = = = + + 7. A uniform magnetic field exists in the region given by ˆ ˆ ˆ B i j k = + + 3 4 5 . A rod of length 5m placed along y-axis is moved along x-axis with constant speed 1 ms–1 . Then induced e.m.f. in the rod is (A) Zero (B) 25 V (C) 5 V (D) 10 V 8. A copper rod AB of length I, pivoted at one end A rotates at constant angular velocity ω, at right angles to a uniform magnetic field of induction B. The emf, developed between the mid point C of the rod and end B is (A) 2 8 B I  (B) 3 4 BωI2 (C) 2 4 B I  (D) 3 8 BωI2 9. A uniform magnetic field is restricted within a region of radius r. The magnetic field changes with time at a rate dB dt . Lood 1 of radius R > r encloses the region r and loop 2 of radius R is outside the region of magnetic field as shown in the figure below. Then the e.m.f. generated is (A) Zero in loop 1 and zero in loop 2 (B) dB 2 r dt −  in loop 1 and dB 2 r dt −  in loop 2 (C) dB 2 R dt −  in loop 1 and zero in loop 2 (D) dB 2 r dt −  in loop 1 and zero in loop 2 PW-AITS_NT-09
10. A thin semicircular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in figure. The potential difference developed across the ring when its speed is v is (A) Zero (B) Bvπr2 /2 and P is at higher potential (C) πrBv and R is at higher potential (D) 2rBv and R is at higher potential 11. A conducting circular loop is placed in a uniform magnetic field B = 0.025 T with its plane perpendicular to the field. The radius of the loop is made to shrink at a constant rate of 1 mm s–1 . The induced e.m.f. when the radius is 2 cm is (A) 2πμV (B) πμV (C) 2  μV (D) 2μV 12. The unit of magnetic flux is (A) Weber/m2 (B) Weber (C) Henry (D) ampere/m 13. A current I = 10 sin(100πt) is passed in a first coil, which induces a maximum emf of 5πV ln in second coil. The mutual inductance between the coil is : (A) 5 mH (B) 10 mH (C) 15 mH (D) 20 mH 14. The coil of self-inductance 2mH and 8mH are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between the coils is : (A) 4 mH (B) 16 mH (C) 10 mH (D) 6 mH 15. A coil having area 2 m2 is placed in a magnetic field which changes from 1Wb/m2 to 4Wb/m2 in an interval of 2 second. The e.m.f. induced in the coil at the fourth second will be : (A) 4 V (B) 3 V (C) 1.5 V (D) 2 V 16. A rectangular coil of 20 turns and area of cross- section 25 sq. cm has a resistance of 100Ω, if a magnetic field which is perpendicular to the plane of coil changes at a rate of 1000 tesla per second, the current in the coil is : (A) 1 A (B) 50 A (C) 0.5 A (D) 5 A 17. The magnetic flux through a circuit of resistance R change by an amount ∆φ in a time ∆t. Then the total quantity of electric charge Q that passes any point in the circuit during the time ∆t is represented by : (A) Q R. t  =  (B) 1 Q . R t  =  (C) Q R  = (D) Q t  =  18. A copper ring is held horizontally and a bar magnet dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnetic while it is passing through the ring is : (A) Equal to that due to gravity (B) Less than that due to gravity (C) More than that due to gravity (D) Depends on the diameter of the ring and the length of the magnet 19. A coil has 2000 turns and area of 7.10 cm2 . The magnetic field perpendicular to the plane of the coil is 0.3 Wb/m2 and takes 0.1 sec to rotate through 180°. The value of the induced e.m.f. will be : (A) 8.4 V (B) 84 V (C) 42 V (D) 4.2 V 20. To electromagnetic induction, the induced e.m.f. in a coil is independent of : (A) Change in the flux (B) Time (C) Resistance of the circuit (D) None of the above 21. v, x, m represent the wavelengths of visible light x-rays and microwaves respectively then (A) m > x > v (B) k > m > x (C) m > v > x (D) v > x > m 22. A parallel plate capacitor is charged by a battery as shown in the figure. If two circular amperian loops x and y are drawn then Bdl  will be zero along (A) x only (B) y only (C) Both x and y (D) Neither x nor y 23. A parallel plate capacitor is charged to 60μC. Due to a radioactive source, the loses charge at the rate
of 1.8 × 10–8 Cs–1 . The magnitude of displacement current is (A) 3.6 × 10–8 Cs–1 (B) 1.8 × 10–8 Cs–1 (C) 4.1 × 10–11 Cs–1 (D) 5.7 × 10–12 Cs–1 24. Light wave travelling along y-direction corresponding E vector at any time is along x- axis, the direction of B vector at that time is along (A) y-axis (B) x-axis (C) z-axis (D) –z-axis 25. In an apparatus, the electric field was found to oscillate with an amplitude of 18 Vm–1 . The magnitude of the oscillation magnetic field will be (A) 4 × 10–6 T (B) 6 × 10–8 T (C) 9 × 10–9 T (D) 11 × 10–11 T 26. Displacement current is set up between the plates of a capacitor when the potential difference across the plates is (A) Maximum (B) Zero (C) Minimum (D) Varying 27. A parallel plate capacitor with circular plates of radius R is being charged as shown. At the instant shown, the displacement current in the region between the plates enclosed between 2 R and R is given by (A) 3 4 i (B) 1 4 i (C) 3i (D) 4 3 i 28. Electromagnetic waves are produced due to (A) A charge at rest (B) A moving charge (C) An accelerated charge (D) None of these 29. According to modified Ampere’s circuital law (iD = displacement current) (A) 0 0 . E C d B dl i dt    =  +       (B) 0 0 . E d B dl dt  =    (C) 0 B dl i . =   (D) 0 . E C D d B dl i i dt    =  +      30. Which of the following is not transported by electromagnetic waves ? (A) Energy (B) Momentum (C) Charge (D) Information not sufficient 31. Which of the following is incorrect about a plane electromagnetic wave ? (A) The electric field and magnetic field have equal average values (B) The electric energy and the magnetic energy have equal average values (C) The electric field and magnetic field both oscillate in same phase (D) The electric field and magnetic field oscillate in opposite phase 32. The ratio of secondary to the primary turns in a transformer is 3 : 2. If the power output be P, then input power neglecting all losses must be equal to (A) 5P (B) P (C) 1.5P (D) 2 5 P 33. The primary and secondary coils of a transformer have 50 and 1500 turns respectively. If the magnetic flux φ linked with the primary coil is given by φ = φ0 + 4t, where φ is in webers, t is time in seconds and φ0 is a constant, the output voltage across the secondary coil is (A) 90 V (B) 120 V (C) 220 V, 500 Hz (D) 2 V, 5 Hz 34. In a series RLC circuit, potential differences across R, L and C are 30 V, 60 V and 100 V respectively as shown in figure. The e.m.f. of source (in volts) is (A) 190 (B) 70 (C) 50 (D) 40 35. In a series RLC circuit, the r.m.s. voltage across the resistor and the inductor are respectively 400 V and 700 V. If the equation for the applied voltage is  =  500 2 sin t , then the peak voltage across the capacitor is