Term
| Can an electron at rest in a magnetic field be set into motion by the magnetic field? What if it were at rest in an electric field? |
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Definition
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Term
If all atoms have electrons that are in motion about an atom, why aren’t all materials
magnetic? |
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Definition
| The net magnetic field created by ordinary materials is zero. c |
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Term
| A strong magnet attracts a paper clip to itself with a certain force. Does the paper clip exert a force on the strong magnet? If not, why not? If so, does it exert as much force on the magnet as the magnet exerts on it? |
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Definition
Equal force; Newton’s third law applies
here. |
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Term
A rectangular loop of wire hangs vertically as shown in the figure. A magnetic field is directed horizontally, perpendicular to the wire, and points out of the page at all points as represented by the symbol ⊙. The magnetic field is very nearly uniform along the horizontal portion of the wire ab (length is 0.1 m) which
is near the center of a large magnet producing the field. The top portion of the wire loop is free of the field. The loop hangs from a balance which measures a downward force (in
addition to the gravitational force) of 3×10−2 N when the wire carries a current 0.2 A. What is the magnitude of the magnet field B at the center of the magnet? |
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Definition
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Term
| A rectangular wire loop with n turns is at rest in a uniform magnetic field B~ of magnitude 4 T that is directed into the page. The loop measures 8 cm by 8 cm, and the plane of the loop is perpendicular to the field, as shown. What is the total magnetic flux Φ through the loop? |
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Definition
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Term
| A circular coil is made of N turns of copper wire as shown in the figure. When viewed from the right the coil is wound counterclockwise. A resistor R is inserted in the copper wire. Initially, a uniform magnetic field of magnitude Bi points horizontally from left-to-right through the perpendicular plane of the coil. During a time interval t the field uniformly changes at a constant rate, until a reversed field is reached equal in magnitude to the initial field. The current in the resistor R |
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Definition
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Term
| Does the voltage output increase when a generator is made to spin faster? |
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Definition
| Yes; according to Faraday’s law of induction, the faster the change of magnetic field in a coil, the greater the induced voltage. |
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Term
| Why does a transformer require alternating voltage? |
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Definition
| Alternating voltage leads to electromagnetic induction which is necessary for the transformer to work |
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Term
| A step-down transformer providing electricity for a residential neighborhood has exactly 2823 turns in its primary. When the potential difference across the primary coil is 5905 V, the potential difference across the secondary is 178 V. How many turns are in the secondary? |
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Definition
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Term
Imagine that Galileo had dropped a bar
magnet (permanent magnetic dipole) and an unmagnetized bar of the same mass and shape down identical resistive metallic (copper) tubes from the Tower of Pisa. Which one would have struck the ground first? |
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Definition
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Term
| A weight suspended from a spring is seen to bob up and down over a distance of 37 cm twice each second. What is its frequency? |
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Definition
frequency=2bobs/sec
frequency=2Hz |
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Term
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Definition
period=1/frequency
period=1/2Hz
period=0.5 seconds |
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Term
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Definition
The amplitude is the distance from the
equilibrium position to maximum displacement:
18.5cm |
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Term
What happens to a piece of driftwood in a
lake with waves? |
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Definition
It will move up and down as a result of
the waves. |
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Term
| How is energy transferred by a wave? |
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Definition
Energy is transferred by the up and down
motion of the wave. |
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Term
| 6.9 waves crash onto a beach every 42.8 seconds. What is their frequency? |
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Definition
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Term
| A violin string playing the note “A” oscillates at 440 Hz. What is the period of the string’s oscillation? |
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Definition
period=1/frequency
period=1/440 |
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Term
The speed of all electromagnetic waves in empty space is 3.00 × 10^8 m/s.
What is the wavelength of radio waves emitted at 81.2 MHz? |
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Definition
lamda=v/f
(wavelength)=velocity/frequency |
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Term
| “Doing the wave” is a common activity in large football stadiums. What type of wave is this? |
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Definition
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Term
| Two speakers are wired to emit identical sounds in unison. The wavelength in air of the sounds is 6 m. Do the sounds interfere constructively or destructively at a distance of 12 m from both speakers? |
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Definition
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Term
| At a distance of 9 m from one speaker and 12m from the other? |
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Definition
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Term
| What requires a physical medium in which to travel? |
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Definition
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Term
| If a bell rings inside a bell jar, we can no longer hear it when the air is pumped out, but we can still see it. What differences in the properties of sound and light does this indicate? |
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Definition
Sound needs a material medium for its
transmission, while light does not. |
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Term
| From the stands of a race track why do you notice smoke from the starter’s gun before you hear it fire? |
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Definition
| Light travels about a million times faster than sound in air. |
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Term
How much more intense is sound at 70 dB
than at 0 dB? |
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Definition
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Term
| In what way do sound waves differ from radio waves? |
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Definition
Sound waves require a medium to travel
and radio waves do not |
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Term
| A flute is essentially a pipe open at both ends. The length of a flute is approximately 66.3 cm. What is the first harmonic of a flute when all keys are closed, making the vibrating air column approximately equal to the length of the flute? The speed of sound in the flute is 344 m/s. |
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Definition
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Term
| What is the second harmonic? |
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Definition
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Term
| What is the third harmonic? |
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Definition
| Three times the first harmonic |
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Term
| A certain note has a frequency of 500 Hz. What is the frequency of a note one octave above it? |
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Definition
1000Hz
A change of an octave corresponds to a
factor of 2 for frequencies |
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Term
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Definition
2000 Hz
f = 4(500 Hz) = 2000 Hz |
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Term
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Definition
250 Hz
f =1/2(500 Hz) = 250 Hz |
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Term
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Definition
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Term
| Would electromagnetic waves exist if changing magnetic fields could produce electric fields, but changing electric fields could not in turn produce magnetic fields? |
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Definition
No; electric and magnetic fields coexist
in electromagnetic waves by field induction. |
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