A source of sound has an intensity I1 and when its sound level is measured at a fixed distance the value found is 70 dB. The source then has its intensity increased to I2 and when its sound level is measured at the same distance the value found is 96 dB. What is the ratio I2/I1?
a. 26 b. 400
c. 600 d. 14
[Ques. 2] If a bar magnet is falling through a loop of wire, the induced current in the loop of wire sets up a field which exerts a force on the magnet. This force between the magnet and the loop will be attractive when
a. the magnet enters the loop.
b. the magnet is halfway through.
c. the magnet is leaving the loop.
d. never.
[Ques. 3] In the afternoon, the decibel level of a busy freeway is 85 dB with 90 cars passing a given point every minute. Late at night, the traffic flow is only 8 cars per minute. What is the late-night decibel level?
a. 200 dB
b. 85 dB
c. 170 dB
d. 74 dB
e. 8.5 dB
[Ques. 4] A bar magnet is falling through a loop of wire with constant velocity. The north pole enters first. As the south pole leaves the loop of wire, the induced current (as viewed from above) will be
a. clockwise.
b. counterclockwise.
c. zero.
d. along the length of the magnet.
[Ques. 5] A common approximation is when the intensity of a sound is doubled, the decibel level increases by 3 . The sound level in a particular location is 100 dB. By what approximate factor is the sound intensity increased if the new decibel level of this sound is 106?
a. 2
b. 3
c. 4
d. 6
[Ques. 6] A bar magnet is falling through a loop of wire with constant velocity. The north pole enters first. The induced current will be greatest in magnitude when the magnet is located so that
a. the loop is near either the north or the south pole.
b. the loop is near the north pole only.
c. the loop is near the middle of the magnet.
d. with no acceleration, the induced current is zero.
[Ques. 7] A sound intensity of 70 dB is observed at a distance d from the source of sound. What sound intensity would be observed at a distance 2d from the source?
a. 68 dB b. 67 dB
c. 64 dB d. 62 dB
[Ques. 8] A planar loop consisting of seven turns of wire, each of which encloses 200 cm2, is oriented perpendicularly to a magnetic field that increases uniformly in magnitude from 14 103 T to 38 103 T in a time of 8.0 103 s. What is the resulting induced current in the coil if the resistance of the coil is 5.0 ?
a. 1.2E2 A
b. 1.2E+0 A
c. 1.3E1 A
d. 8.4E2 A
e. 7.7E1 A
[Ques. 9] What sound level change corresponds to a factor of two change in intensity?
a. 0.2 dB
b. 2.0 dB
c. 3.0 dB
d. 11 dB
e. 20 dB
[Ques. 10] A flat coil of wire consisting of 15 turns, each with an area of 40 cm2, is positioned perpendicularly to a uniform magnetic field that increases its magnitude at a constant rate from 1.5 T to 5.1 T in 2.0 s. If the coil has a total resistance of 0.20 , what is the magnitude of the induced current?
a. 7.65E1 A
b. 5.40E+1 A
c. 5.40E1 A
d. 8.64E2 A
e. 2.16E1 A
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