# Shared Flashcard Set

## Details

2nd Semester Midterm 2
Physics for Non-Science Majors at UT Austin (quest based)
34
Physics
03/20/2013

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?
Definition
 no; yes
Term
 If all atoms have electrons that are in motion about an atom, why aren’t all materialsmagnetic?
Definition
 The net magnetic ﬁeld created by ordinary materials is zero. c
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?
Definition
 Equal force; Newton’s third law applieshere.
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) whichis 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 (inaddition 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?
Definition
 1.5TB=F/Il
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?
Definition
 0.0256 T · m2Φ = B A
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
Definition
 ﬂows from left to right
Term
 Does the voltage output increase when a generator is made to spin faster?
Definition
 Yes; according to Faraday’s law of induction, the faster the change of magnetic ﬁeld in a coil, the greater the induced voltage.
Term
 Why does a transformer require alternating voltage?
Definition
 Alternating voltage leads to electromagnetic induction which is necessary for the transformer to work
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?
Definition
 ∆V2N2=∆V1N1
Term
 Imagine that Galileo had dropped a barmagnet (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?
Definition
 The unmagnetized bar
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?
Definition
 frequency=2bobs/secfrequency=2Hz
Term
 What is its period?
Definition
 period=1/frequencyperiod=1/2Hzperiod=0.5 seconds
Term
 What is its amplitude?
Definition
 The amplitude is the distance from theequilibrium position to maximum displacement:18.5cm
Term
 What happens to a piece of driftwood in alake with waves?
Definition
 It will move up and down as a result ofthe waves.
Term
 How is energy transferred by a wave?
Definition
 Energy is transferred by the up and downmotion of the wave.
Term
 6.9 waves crash onto a beach every 42.8 seconds. What is their frequency?
Definition
 6.9/42.8
Term
 A violin string playing the note “A” oscillates at 440 Hz. What is the period of the string’s oscillation?
Definition
 period=1/frequencyperiod=1/440
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?
Definition
 lamda=v/f(wavelength)=velocity/frequency
Term
 “Doing the wave” is a common activity in large football stadiums. What type of wave is this?
Definition
 Transverse wave.
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?
Definition
 Constructively
Term
 At a distance of 9 m from one speaker and 12m from the other?
Definition
 Destructively
Term
 What requires a physical medium in which to travel?
Definition
 sound
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?
Definition
 Sound needs a material medium for itstransmission, while light does not.
Term
 From the stands of a race track why do you notice smoke from the starter’s gun before you hear it ﬁre?
Definition
 Light travels about a million times faster than sound in air.
Term
 How much more intense is sound at 70 dBthan at 0 dB?
Definition
 1 × 10^7
Term
 In what way do sound waves diﬀer from radio waves?
Definition
 Sound waves require a medium to traveland radio waves do not
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.
Definition
 v/2L
Term
 What is the second harmonic?
Definition
 Twice the first harmonic
Term
 What is the third harmonic?
Definition
 Three times the first harmonic
Term
 A certain note has a frequency of 500 Hz. What is the frequency of a note one octave above it?
Definition
 1000HzA change of an octave corresponds to afactor of 2 for frequencies
Term
 Two octaves above it?
Definition
 2000 Hzf = 4(500 Hz) = 2000 Hz
Term
 One octave below it?
Definition
 250 Hzf =1/2(500 Hz) = 250 Hz
Term
 Two octaves below it?
Definition
 f =1/4(500 Hz) = 125 Hz
Term
 Would electromagnetic waves exist if changing magnetic ﬁelds could produce electric ﬁelds, but changing electric ﬁelds could not in turn produce magnetic ﬁelds?
Definition
 No; electric and magnetic ﬁelds coexistin electromagnetic waves by ﬁeld induction.
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