Tiêu đề 4-magnetic-effect-of-current-.pdf ✅

Magnetic Effect of Current 1. Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field B = B0kˆ ⋅ v1 and v2 are velocity components of the two particles parallel to magnetic field. (A) They have equal z-components of momenta (B) They must have equal charges (C) They necessarily represent a particle- antiparticle pair (D) The charge to mass ratio satisfy : m1V1 q1 + m2V2 q2 = 0 2. A wire carrying current I is tied between points P and Q and is in the shape of a circular arc of radius R due to a uniform magnetic field B (perpendicular to the plane of the paper, shown by XXX ) in the vicinity of the wire. If the wire subtends an angle 2θ0 at the centre of the circle (of which it forms an arc) then the tension in the wire is : (A) IBR (B) IBR sin θ0 (C) IBR 2sin θ2 (D) IBRθ0 sin θ0 3. A charged particle with charge q enters a region of constant, uniform and mutually orthogonal fields E⃗ and B⃗ with a velocity v perpendicular to both E⃗ and B⃗ , and comes out without any change in magnitude or direction of v . Then : (A) v = E⃗ × B⃗ B2 (B) v = B⃗ × E⃗ B2 (C) v = E⃗ × B⃗ E2 (D) v = B⃗ × E⃗ E2 4. Biot-Savart law indicates that the moving electrons (velocity v ̅ ) produce a magnetic field B ̅ such that (A) B ̅ ⊥ v ̅ (B) B ̅ ∥ v ̅ (C) it obeys inverse cube law (D) it is along the line joining the electron and point of observation 5. Two long straight parallel wires, carrying (adjustable) current I1 and I2, are kept at a distance d apart. If the force F between the two wires is taken as positive when the wires repel each other and negative when the wires attract each other, the graph showing the dependence of F, on the product I1,I2, would be : (A) (B) (C)
(D) 6. Two long conductors, separated by a distance d carry currents I1 and I2 and in the same direction. They exert a force F on each other. Now the current in one of them is increased to two times and its direction is reversed. The distance is also increased to 3d. The new value of the force between them is : (A) −2F (B) − 2F 3 (C) F 3 (D) − F 3 7. A current carrying circular loop of radius R is placed in the x − y plane with centre at the origin. Half of the loop with x > 0 is now bent so that it now lies in the y-z plane. (A) The magnitude of magnetic moment now diminishes (B) The magnetic moment does not change (C) The magnitude of B at (0,0, . z), z >> increases (D) The magnitude of B at (0,0, z), z > R is unchanged 8. A magnetic needle lying parallel to a magnetic field requires W unit of work to turn it through 60∘ . The torque needed to maintain the needle in this position will be : (A) ( √3 2 )W (B) √3W (C) W (D) 2W 9. A conductor lies along the z-axis at −1.5 ≤ z < 1.5 m and carries a fixed current of 10.0 A in −az direction (see figure). For a field B = 3.0 × 10−4e −0.2xayT, find the power required to move the conductor at constant speed to x = 2.0 m, y = −0 in 5 × 10−3 s. Assume parallel motion along the x-axis. (A) 1.57 W (B) 2.97 W (C) 14.85 W (D) 29.7 W 10. Wire 1 and 2 carrying currents I1 and I2 respectively are inclined at an angle θ to each other. What is the force on a small element dl of wire 2 at a distance r from wire 1 (as shown in figure) due to the magnetic field of wire 1 ? (A) μ0 2πr I1I2dltan θ (B) μ0 2πr I1I2dlsin θ (C) μ0 2πr I2I2dlcos θ (D) μ0 4πr I1I2dlsin θ 11. An electron is projected with velocity v0 in a uniform electric field E perpendicular to the field. Again it is projected with velocity v0 perpendicular to a uniform magnetic field B. If r1 is initial radius of curvature just after entering in the electric field and r2 is initial radius of curvature just after entering in magnetic field then the ratio r1/r2 is equal to : (A) Bv0 2 E (B) B E (C) Ev0 B (D) Bv0 E 12. An electron is projected with uniform velocity along the axis of a current carrying long solenoid. Which of the following is true? (A) The electron will be accelerated along the axis (B) The electron path will be circular about the axis (C) The electron will experience a force at 45∘ to the axis and hence execute a helical path (D) The electron will continue to move with uniform velocity along the axis of the solenoid
13. A proton (mass m ) accelerated by a potential difference V flies through a uniform transverse magnetic field occupies a region of space by width d. If α be the angle of deviation of proton from initial direction of motion (see figure), the value of sin α will be : (A) B 2 √ q mV (B) B d √ q 2mV (C) Bd√ q 2mV (D) qV√ Bd 2m 14. A rectangular loop of sides 10 cm and 5 cm carrying a current I of 12 A is placed in different orientations as shown in the figure blow : If there is a uniform magnetic field of 0.3T in the positive z direction, in which orientations the loop would be in (i) stable equilibrium and (ii) unstable equilibrium. (A) (2) and (4), respectively (B) (2) and (3), respectively (C) (1) and (2), respectively (D) (1) and (3), respectively 15. OABC is a current carrying square loop. An electron is projected from the centre of loop along its diagonal AC as shown. Unit vector in the direction of initial acceleration will be : (A) kˆ (B) − ( iˆ+jˆ √2 ) (C) − kˆ (D) iˆ+jˆ √2 16. If in a circular coil A of radius R, current I is flowing and in another coil B of radius 2R a current 2I is flowing, then the ratio of the magnetic fields, BA and BB produced by them will be : (A) 1 (B) 2 (C) 1/2 (D) 4 17. A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B. It is then bent into a circular loop of n turns. The magnetic field at the centre of the coil will be : (A) nB (B) n 2B (C) 2nB (D) 2n 2B 18. Magnetic field at the centre of a circular loop of area A is B. Then magnetic moment of the loop will be : (A) BA 2 μ0π (B) BA μ0 √A (C) BA√A μ0π (D) 2BA μ0 √ A π 19. In a cyclotron, a charged particle (A) Undergoes acceleration all the time (B) Speeds up between the dees because of the magnetic field (C) Speeds up in a dee (D) Slows down within a dee and speeds up between dees 20. A magnetic needle is kept in a non-uniform magnetic field. It may experience : (A) A torque but not a force (B) Neither a force nor a torque
(C) A force and a torque (D) A force but not a torque 21. A helium ion and a Hydrogen ion are accelerated from rest through a potential difference of V to velocities of UHe and UH respectively. What will be the ratio of UHe to UH : (A) 1/4 (B) 1/√2 (C) √2 (D) 2 22. A long straight wire of radius a carries a steady current I. The current is uniformly distributed across its cross-section. The ratio of the magnetic field at distances a 2 and a from the axis is : (A) 1/4 (B) 4 (C) 1 (D) 1/2 23. Two long current carrying thin wires, both with current I in opposite direction, are held by insulating threads of length L and are in equilibrium as shown in the figure, with threads making an angle θ with the vertical. If wire have mass λ per unit length then the value of I is : (g = gravitational acceleration ) (A) 2√ πgL μ0 tan θ (B) √ πλgL μ0 tan θ (C) sin θ√ πλgL μ0cos θ (D) 2sin θ√ πλgL μ0cos θ 24. A particle of mass M and charge Q moving with velocity v describes a circular path of radius R when subjected to a uniform transverse magnetic field of induction B. The work done by the field when the particle completes one full circle is : (A) ( Mv 2 R ) 2πR (B) Zero (C) BQ2πR (D) BQv2πR 25. A circular current loop of magnetic moment M is in an arbitrary orientation in an external magnetic field B. The work done to rotate the loop by 30∘ about an axis perpendicular to its plane is : (A) MB (B) √3 MB 2 (C) MB 2 (D) zero 26. A galvanometer has a 50 division scale. Battery has no internal resistance. It is found that there is deflection of 40 divisions when R = 2400Ω. Deflection becomes 20 divisions when resistance taken from resistance box is 4900Ω. Then we can conclude. (A) Current sensitivity of galvanometer is 20μA/ division (B) Resistance of galvanometer is 200Ω. (C) Resistance required on R.B for a deflection of 10 divisions is 9800Ω. (D) Full scale deflection current is 2 mA 27. A 50Ω resistance is connected to a battery of 5 V. A galvanometer of resistance 100Ω is to be used as anmeter to measure current through the resistance, for this resistance rs is connected to the galvanometer. Which of the following connections should be employed if the measured current is within 1% of the current without the ammeter in the circuit? (A) rs = 0.5Ω in series with the galvanometer (B) rs = 1Ω in series with galvanometer (C) rs = 1Ω in parallel with it galvanometer (D) rs = 0.5Ω in parallel with the galvanometer 28. At a specific instant emission of radioactive compound is deflected in a magnetic field. The compound can emit : I. Electrons II. Protons III. He2+ IV. Neutrons The emission at the instant can be : (A) I, II, III (B) I, II, III, IV