# Physics Principles and Problems 2009

## Chapter 24: Magnetic Fields

### Chapter Test Practice

 1 Magnetic field lines travel from __________. Need a Hint? A) north pole to south pole through the magnet B) in a circle around the entire magnet, while never touching the magnet C) south pole to north pole outside the magnet D) north pole to south pole outside the magnet 2 What happens if you cut a magnet in half? Need a Hint? A) it becomes demagnetized B) you get a separate south pole and a separate north pole C) you get monopoles D) you get two magnets 3 Magnetic domains are __________ in a magnet. Need a Hint? A) scattered B) aligned C) misaligned D) random 4 The second right hand rule is used to determine the __________. Need a Hint? A) direction of current B) direction of magnetic force C) direction of the magnetic field D) amount of current 5 Which of the following phenomena is NOT illustrated in Figure 24-9? (10.0K) Need a Hint? A) A current causes a magnetic field. B) The magnetic field caused by a wire is stronger closer to the wire. C) Magnetic field lines form closed loops. D) In space, magnetic field lines point from north to south. 6 How can you make a magnet out of a long strand of wire and an iron bar? Need a Hint? A) Send a current through the bar. B) Spin the bar over the wire as a current runs through it. C) Wrap the wire around the bar, and send a current through it. D) Attach the wire to either end of the bar, and send a current through it. 7 If current is reduced in an electromagnet, what happens to the magnetic field strength? Need a Hint? A) it remains the same B) it remains the same C) it is reduced D) it increases 8 A nail that touches a magnet will __________. Need a Hint? A) melt B) generate an electric current C) demagnetize the magnet D) become polarized 9 A south pole will __________ another south pole. Need a Hint? A) attract B) ignore C) destroy D) repel 10 According to geologic evidence, Earth's magnetic poles __________. Need a Hint? A) have switched over the years B) have only recently appeared C) have remained the same D) have remained the same 11 The ___________ is proportional to the strength of the magnetic field. Need a Hint? A) magnetic flux per unit area B) magnetic flux C) mass of the magnet D) size of the magnet 12 A 10-m long wire carrying 5 A of current is at right angles to a uniform magnetic field of 0.01 T. What is the magnitude of the force on the wire? Need a Hint? A) 0.05 N B) 0.5 N C) 50 N D) 5 N 13 In the figure below, if the magnetic poles were reversed AND the current in the wire were reversed, what would the direction of the magnetic force be? (5.0K) Need a Hint? A) up B) down C) left D) right 14 Two straight wires that are parallel to each other are carrying currents in opposite directions. What happens to the wires? Need a Hint? A) They stop carrying current because the current directions cancel each other out. B) Nothing happens. C) They repel each other. D) They attract each other. 15 If a magnetic field points upward and the current is to your left, the force is __________. Need a Hint? A) away from you B) to your left C) to your right D) toward you 16 A magnetic field exerts a force on __________. Need a Hint? A) only electrons B) all charged particles, regardless of size C) only protons D) only small particles 17 A beam of protons travels at 3.5 × 10E6 m/s through a uniform magnetic field of 5.7×10-2 T. The beam of electrons is perpendicular to the field. How strong is the force acting on each proton? Need a Hint? A) -6.4×10-14 N B) 1.6×10-12 N C) 3.2×10-14 N D) 3.2×10-12 N 18 The speed of an electric motor is controlled by varying the __________ through the motor. Need a Hint? A) resistance B) direction of the north pole C) current D) voltage 19 A(n) __________ uses electromagnetism to measure small currents. Need a Hint? A) galvanometer B) ohmmeter C) ammeter D) voltmeter 20 How does an electric motor rotate 360 degrees? Need a Hint? A) A galvanometer changes the direction. B) As the split ring reaches vertical, each half of the ring switches brushes and reverses the direction of current in the wire loop. C) A magnet moves through an electrical field. D) A wire spins the wheel. 21 In the figure below, if the magnetic poles were reversed, what would the direction of the magnetic force be? (5.0K) Need a Hint? A) right B) down C) up D) left 22 A straight wire that carries a 4.6-A current is in a uniform magnetic field oriented at right angles to the wire. The magnetic field has a strength of 1.2 T. If the force exerted on the wire is 0.60 N, what length of wire is in the magnetic field? Need a Hint? A) 0.16 m B) 0.11 m C) 2.3 m D) 3.3 m 23 An electron moving at 5.6×107 m/s travels through a uniform magnetic field of 1.4 T at right angles to the field. How strong is the force that acts on the electron? Need a Hint? A) -1.3×10-11 N B) -3.7×10-11 N C) 1.5×10-11 N D) 2.2×10-11 N 24 If there were no current in the wire in the figure below, what impact, if any, would that have on the magnetic force shown? (5.0K) Need a Hint? A) The force would remain the same. B) The force would be directed toward the south pole shown. C) The force would be directed toward the south pole shown. D) The force would be reduced, but still point upwards. 25 A magnetic field is generated __________ the direction of current in a wire. Need a Hint? A) in the same direction as B) opposite of C) parallel to D) perpendicular to 26 If a current is traveling toward you in a wire, what is the direction of the magnetic field? Need a Hint? A) toward you B) counterclockwise C) away from you D) clockwise 27 The force on an electron from a magnetic field is __________. Need a Hint? A) so small it cannot be measured B) opposite the direction indicated by the third right hand rule C) in the same direction as the magnetic field D) in the same direction as indicated by the third right hand rule 28 In the figure below, if the current in the wire were reversed, what would the direction of the magnetic force be? (5.0K) Need a Hint? A) down B) left C) right D) up 29 A straight current-carrying wire is in a uniform magnetic field oriented at right angles to the wire. 0.14 m of wire is in the 0.72-T field. If the force on the wire is 0.33 N, what is the current in the wire? Need a Hint? A) 0.064 A B) 3.3 A C) 0.13 A D) 1.7 A
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