Physics-DPP-3-Magnetism

PHYSICS Topic: Magnetism Date: 1. An observer A and a charge Q are fixed in a stationary frame F1. An observer B is fixed in a frame F2, which is moving with respect to F1. (a) Both A and B will observe electric fields. (b) Both A and B will observe magnetic fields. (c) Neither A nor B will observe magnetic fields. (d) B will observe a magnetic field, but A will not. 2. A long straight wire carries a current along the x-axis. Consider the points A(0, 1, 0), B(0, 1, 1), C(1, 0, 1) and D(1, 1, 1). Which of the following pairs of points will have magnetic fields of the same magnitude? (a) A and B (b) A and C (c) B and C (d) B and D 3. In the previous question, if the current is i and the magnetic field at D has magnitude B, (a) B = μ0i 2 2π (b) B = μ0i (c) B is parallel to the z-axis (d) B makes an angle of 45º with the xy plane 4. Two long parallel wires, AB and CD carry equal currents in opposite directions. they lie in the xy plane, parallel to the x-axis, and pass through the points (0 –a, 0) and (0, a, 0) respectively. The resultant magnetic field is (a) zero on the x-axis (b) maximum on the x-axis (c) directed along the z-axis at the origin, but not at other points on the z-axis. (d) directed along the z-axis at all points on the z-axis 5. A wire PQRS carrying a current I runs along three edges of a cube of side l as shown in figure. There exists a uniform magnetic field of magnitude B along are of the sides of the cube. The magnitude of the force acting on the wire is (a) zero (b) BIl (d) 2 BI l PHYSICS Topic: Magnetism Date: 6. In the loops shown, all curved sections are either semicircles or quarter circles. All the loops carry the same current. The magnetic fields at the centres have magnitudes B1, B2, B3 and B4. (a) B4 is maximum (b) B3 is minimum (c) B4 > B1 > B2 > B3 (d) B1 > B4 > B3 > B2 7. A long straight conductor, carrying a current i, is bent to form an almost complete circular loop of radius r on it. The magnetic field at the centre of the loop (a) is directed into the paper (b) is directed out of the paper μ0i æç 1 ö÷ (c) has magnitude ç1- ÷ 2r è π ø μ0i æç 1 ö÷ (d) has magnitude ç1+ ÷ 2r è π ø 8. A long, straight, hollow conductor (tube) carrying a current has two sections A and C of unequal cross-sections joined by a conical section B. 1, 2 and 3 are points on a line parallel to the axis of the conductor. The magnetic fields at 1, 2 and 3 have magnitudes B1, B2 and B3. (a) B1 = B2 = B3 (b) B = B  B 1 1 3 (c) B1 < B2 < B3 (d) B2 cannot be found unless the dimensions of the section B are known. 9. A conductor ABCDEF, shaped as shown, carries a current i. It is placed in the xy plane with the ends A and E on the x-axis. A uniform magnetic field of magnitude B exists in the region. The force acting on it will be (a) zero, if B is in the x-direction (b) Bi in the z-direction, if B is in the y-direction (c) Bi in the negative y-direction, if B is in the z-direction (d) 2aBi, if B is in the x-direction 10. A conducting gas is in the form of a long cylinder. Current flows through the gas along the length of the cylinder. The current is distributed uniformly across the cross-section of the gas. Disregard thermal and electrostatic forces among the gas molecules. Due to the magnetic fields set up inside the gas and the forces which they exert on the moving ions, the gas will tend to (a) Expand (b) Contract (c) Expand and contract alternately (d) None of the above PHYSICS Topic: Magnetism Answer Key Date: 1. (a, d) 2. (b, d) 3. (a, d) 4. (b, d) 5. (c) 6. (a, b, c) 7. (b, c) 8. (a) 9. (a, b, c) 10. (b)

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