1. Which device creates a current based on the principle of electromagnetic induction?

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1 Assignment 2 Electromagnetism Name: 1. Which device creates a current based on the principle of electromagnetic induction? A) galvanometer B) generator C) motor D) solenoid 2. The bar magnet below enters a solenoid from the left. What will be the direction of the induced current in the solenoid? A) A B) B C) C D) D 3. The bar magnet below is pulled out of a solenoid as shown. Given the direction of the induced current in the solenoid, what will be the polarity of X and Y? X Y A) north north B) north south C) south north D) south south 4. A bar magnet is moved away from a coil as shown. What is the direction of the induced current through the resistor and the polarity of the left end of the coil? Direction of Polarity of left induced current end of coil A) X to Y north B) X to Y south C) Y to X north D) Y to X south 5. The diagram shows a bar magnet falling through an aluminum pipe. Electric currents are induced in the pipe immediately above and below the falling magnet. In which direction do these currents flow? ABOVE THE MAGNET A) 1 3 B) 1 4 C) 2 3 D) 2 4 BELOW THE MAGNET 6. Two hollow-core solenoids, A and B, are connected by a wire, as shown in the diagram below. Two bar magnets, 1 and 2, are suspended just above the solenoids. What force will magnet 2 experience as magnet 1 falls through solenoid A? A) attraction by an electric force toward solenoid B B) attraction by a magnetic force toward solenoid B C) repulsion by an electric force away from solenoid B D) repulsion by a magnetic force away from solenoid B

2 7. As switch S is closed, in what direction does the compass needle point and what is the direction of the current through resistor R? COMPASS NEEDLE DIRECTION CURRENT DIRECTION THROUGH R A) west From 1 to 2 B) west From 2 to 1 C) east From 1 to 2 D) east From 2 to 1 8. In the picture to the right the N pole of a magnet is being pulled out of the coil. Which of the next four pictures shows the correct illustration of the coil poles and the induced current in the coil? 9. In the diagram below, a permanent magnet is balanced above a coil of wire. When the switch is closed, the magnet is deflected upward. What is the magnetic polarity at the hollow core (X) and the charges at the battery terminal (Y)?

3 10. A student drops a bar magnet downward through a 1.0 m long plastic tube and then through a 1.0 m long copper tube of equal diameter. What will happen to the magnet in each situation? A) come to rest about halfway down each tube B) take longer to fall through the copper tube C) take longer to fall through the plastic tube D) take the same time to fall through each tube 11. Which of the following factors does not affect the size of the induced current in a coil? A) number of turns in the coil B) size of the inducing field C) rate of change of the inducing field D) direction of the windings in the coil 12. A coil is connected to a galvanometer. When a permanent magnet is held steady in the center of the coil, what will the galvanometer indicate? A) A steady current. B) A decreasing current. C) An alternating current. D) No current. 13. Which of the statements below the picture is the correct one for the instant that the switch is closed in the primary circuit? A) the top of the secondary coil becomes a N pole and the induced current exits the top of the coil B) the top of the secondary coil becomes a S pole and the induced current exits the top of the coil C) the top of the secondary coil becomes a N pole and the induced current exits the bottom of the coil D) the top of the secondary coil becomes a S pole and the induced current exits the bottom of the coil 14. Which device could be used to convert an AC generator to a DC generator? A) armature B) commutator C) slip ring D) transformer 15. What is the main difference between a DC generator and an AC generator? A) An AC generator doesn't have any brushes B) An AC generator doesn't have a commutator C) A DC generator doesn't have any brushes D) A DC generator doesn't have any field magnets (permanent magnets) 16. The graph below shows the output from a generator. What is true of the generator? A) AC with multiple loops C) DC with multiple loops B) AC with a single loop D) DC with a single loop

4 17. The graph below shows the emf produced by a simple generator made with only one loop in the coil and a permanent magnet producing the stationary field. What is the period of one rotation of the generator and does the generator have solid-slip rings or a split-ring commutator? A) 0.05 s Solid slip ring B) 0.10 s Solid slip ring C) 0.05 s Split ring D) 0.10 s Split ring PERIOD COMMUTATOR TYPE 18. Cell phones convert voice into electromagnetic impulses with a frequency range between 800 MHz to 2100 MHz. What is the wavelength of the most energetic electromagnetic waves transmitted by cell phones? A) 0.14 cm B) 0.38 cm C) 14 cm D) 38 cm 19. A spacecraft orbiting Earth has a coil of wire in it. An astronaut measures a small current in the coil although there is no battery connected to it and there are no magnets on the spacecraft. Explain what causes the current. 20. The possible hazardous effects of exposure to electromagnetic waves such as radio frequency radiation from the antenna of a cell phone have yet to be determined. Describe two ways a cell phone user could reduce their risk of exposure to electromagnetic waves from the antenna. 21. Two people are talking to one another on their identical cell phones. Person A holds the phone 2.0 cm from his ear, while Person B holds it 6.0 cm from her ear. Explain which person will receive the greatest intensity of radio frequency radiation and state by what factor it is greater.

5 22. Faraday s ring shows two coils of insulated wire wrapped around an iron core, with a galvanometer in the bottom circuit. Use Lenz Law to predict the direction of the induced current in the bottom coil when the switch is closed. Explain your reasoning. 23. In the two situations below, a wire is pulled through a region with a given magnetic field as shown. Determine whether a current will be induced in the wire and show its direction. 24. Two identical magnets are dropped simultaneously through the hollow tubes as shown below. A student observes that both magnets fall at different rates. (a) Which magnet should fall faster? (b) Using your knowledge of physics principles, how could this observation be explained?