Summary




































Knight2 33.cq.12a
The figure shows a current-carrying wire passing between two bar magnets. Is there a force on the wire? If so, in what direction? If not, why not? Knight2 33.CQ.12a
A. Yes ... upward
B. Yes ... to the right
C. Yes ... downward
D. Yes ... to the left
E. No, because B is perpendicular to I
F. No, because B = 0 at the wire
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klm
Current is produced in a loop when a magnet is moved into the loop. Where does the electrical energy come from?
A. Energy stored in the wire atoms.
B. Energy stored in the magnet
C. Energy in the magnet's motion.
D. Energy in electric waves.
Answer



















klm
A light bulb attached to a coil lights up when it is brought near a solenoid that carries an alternating current. Where does the electrical energy come from?
A. Energy stored in the wire atoms.
B. Energy stored in the magnet
C. Energy in the magnet's motion.
D. Energy in electric waves.
Answer



















PSE6 31.6
In what time must a 0.20 T magnetic field be turned off in order to induce a 10 kV emf in a solenoid of 500 turns and 10 cm diameter?
A. 5.33 µs
B. 78.5 µs
C. 335 µs
D. 22.2 ms
Answer



















Walker5e 23.19
A 120-turn coil oriented with its plane perpendicular to a 0.33-T magnetic field has an area of 0.050 m². Calculate the average induced emf in this coil if the magnetic field reverses its direction in 0.11 s.
A. 36 V
B. 18 V
C. 0.44 V
D. 0.30 V
Answer

























 



C. Yes ... downward

The current is into the page, while the magnetic field is toward the right (out of the north pole and into the south pole). Use the right hand rule to find that the magnetic force per unit length I × B points downward.




















 



C. Energy in the magnet's motion.
If the magnet does not move, there is no changing magnetic flux, and no induced current in the coil. In this way Faraday's law explains how mechanical energy can be converted to electrical energy.



















 



D. Energy in electric waves.
No mechanical energy is involved. Instead, the solenoid produces a changing magnetic field, which induces a changing electric field that circulates around it. That changing electric field represents a displacement current that induces a changing magnetic field, and so on. The energy propagates in the form of a wave, with the solenoid acting as the source of the waves and the wire loop the "antenna." The changing electric field drives sufficient alternating current in the wire loop to light the bulb.



















 



B. 78.5 µs






















 



A. 36 V
solution equation