CHAPTER 4: MAGNETIC FIELD

Size: px

Start display at page:

Download "CHAPTER 4: MAGNETIC FIELD"

Allen Payne
5 years ago
Views:

1 CHAPTER 4: MAGNETIC FIELD PSPM II 2005/2006 NO FIGURE 3 A copper rod of mass 0.08 kg and length 0.20 m is attached to two thin current carrying wires, as shown in FIGURE 3. The rod is perpendicular to a uniform magnetic field of 0.60 T. Determine the magnitude and direction of the electric current to keep the copper rod fixed and stay horizontal. [Ans: I = A; To the right.] [3 marks] PSPM II 2005/2006 NO. 11(C) 11 (c) A rectangular coil of 30 turns has a dimension of 1.0 cm 1.5 cm. The coil experiences a torque of N m when placed in a magnetic field of 0.35 T. What is the current in the coil? [Ans: I = A] PSPM II 2006/2007 NO. 12(A) 12. (a) FIGURE 9 FIGURE 9 shows two long parallel wires 2 cm apart. Wire P carries a current 7 A to the right. Point C is 3 cm from wire Q and in the same plane as wire P and Q. Determine the magnitude and direction of current in wire Q so that the magnetic field at C is zero. [Ans: I Q = 4. 2 A; Towards left.] [6 marks] PCH 1

2 PSPM II 2007/2008 NO. 12(A) 12. (a) A circular coil of 100 turns and cross-sectional area of 2.0 cm 2 carrying a 50 ma current is placed in a magnetic field of 0.5 T parallel to the plane of the coil. Calculate the torque acting on the coil. [Ans: τ = N m] PSPM II 2008/2009 NO FIGURE 2 FIGURE 2 shows two long parallel wires, each carrying a 5 A current in opposite direction. Determine the magnetic field, B at point P, 3 cm from both wires. [Ans: B P = T; Out of paper] PSPM II 2010/2011 NO. 12(A),(B) 12. (a) A 4 cm 8 cm rectangular coil with 120 turns carrying 0.5 ma current is placed in a uniform magnetic field 0.6 T. Calculate the required torque to hold the coil s plane parallel to the field. [Ans: τ = N m] [3 marks] (b) A kg particle of charge 5 nc and velocity 3500 m s 1 enters a region of uniform magnetic field T perpendicular to the field. (i) Calculate the radius of the path of the particle. [Ans: R = m] Explain whether there is any change in the particle s path when the magnetic field is reduced to half and the particle s velocity is increased four times. [Ans: R 2 = 8 R] [5 marks] PSPM II 2011/2012 NO (a) Define one ampere. PCH 2

3 (b) FIGURE 3 A proton moving at m s 1 along the x-axis enters a region of uniform magnetic field of magnitude 1.8 T. The direction of the magnetic field is 30 with the x-axis and parallel to the xy-plane as shown in FIGURE 3. (i) Determine the magnitude and direction of the magnetic force on the proton. [Ans: F = N; in the positive z-direction] If the proton is replaced by an electron moving at the same velocity, compare the magnetic force on the electron to that of the proton. Explain your answer. (iii) Does the speed of the proton be affected by the magnetic field? Explain your answer. [9 marks] (c) A 40 m electric cable carries a current of 28 A from west to east. The earth magnetic field is 50 μt, horizontal and directed from south to north. Determine (i) the magnitude and direction of the magnetic force on the cable. [Ans: F = N; upward] the magnetic force on the cable if it is parallel to the direction of the magnetic field. [Ans: F = 0 N] PSPM II 2012/2013 NO (a) FIGURE 4 PCH 3

4 FIGURE 4 shows a long straight wire carrying a current of I 1 = 4.0 A is placed to the left of a circular loop. The loop has a diameter of d = 0.04 m and carrying a current of I 2 = 2.0 A. Determine the magnitude and direction of the net magnetic field at the center of the loop. [Ans: B = T; into the page] [7 marks] (b) FIGURE 5 FIGURE 5 shows a proton with a speed of m s 1 entering a region of a uniform magnetic field between two plates. The plates are separated by a distance of 0.18 m. (i) Determine the direction of the magnetic force on the proton and sketch its trajectory when it enters the region between the plates. What is the maximum magnitude of the magnetic field so that the proton does not hit the opposite plate? [Ans: B = T] [8 marks] PSPM II 2013/2014 NO (a) (i) In what condition would a charged particle experience a magnetic force? Two charged particles moving in the same direction are projected perpendicularly into a uniform magnetic field. If the particles are deflected in opposite directions, what can you say about them? Explain your answer. (b) A circular loop L 1 of radius 5 cm carries a 15 A current. (i) Calculate the magnetic field at its center. [Ans: B 1 = T] FIGURE 4 PCH 4

5 Another loop L 2 of radius 1.5 cm, having 50 turns and carrying a 2 A current is placed at the center of loop L 1 as shown in FIGURE 4. What will be the resultant magnetic field at their common center if the two currents flow in the same direction? [Ans: B resultant = T] (iii) If loop L 1 in FIGURE 4 is fixed but loop L 2 is free to turn about its central axis, what will be the torque on loop L 2 when its plane is parallel to loop L 1? [Ans: τ = N m] [6 marks] (c) A 2 A current flows towards left in a wire having a mass per unit length of 0.5 g cm 1. If the wire is placed horizontally on a table, what are the magnitude and direction of the minimum magnetic field needed to float the wire? [Ans: B = T; or y or (out of page)] [5 marks] PSPM II 2014/2015 NO (a) Sketch the magnetic field lines for a current-carrying (i) straight wire. solenoid. (b) A two turns circular coil was made from a 3 m long wire. Calculate the magnetic field strength at the center of the coil if it carries 0.5 A current. [Ans: B = T] [3 marks] (c) FIGURE 5 FIGURE 5 shows two wires separated by 12 cm carrying currents of 3.5 A in opposite directions. (i) Determine the direction and magnitude of the net magnetic field at a point midway between the wires. [Ans: B net = T; Into the page] Calculate the magnitude of the net force per unit length experienced by the wires. (d) [Ans: F l = N m 1 ] [6 marks] FIGURE 6 PCH 5

6 FIGURE 6 shows an electron travelling in a region of uniform electric and magnetic fields which are perpendicular to one another. The strength of electric field and magnetic field are V m 1 and T respectively. (i) Calculate the velocity of electron. [Ans: v = m s 1 ] Calculate the kinetic energy of electron. [Ans: KE = J] (iii) If the electric field is removed, determine the magnitude and direction of the magnetic force on the electron. [Ans: F = N; Towards the left plate] PCH 6

2. Draw the Magnetic Field lines created by the below two bar magnets. Homework 3. Draw the Magnetic Field lines created by the below bar magnets.

Chapter Problems Magnetic Fields 1. Draw the Magnetic Field lines created by the below bar magnet. S N 2. Draw the Magnetic Field lines created by the below two bar magnets S N N S 3. Draw the Magnetic