Final Review Flashcards
A wire loop moves at constant velocity without rotation through a constant magnetic field. The induced current in the loop will be
zero
Two loops of wire are moving in the vicinity of a very long straight wire carrying a steady current (Figure 1).
(a) Find the direction of the induced current in loop C.
(b) Find the direction of the induced current in loop D.
zero;clockwise
A square loop moves to the right from an area where B⃗ =0, completely through a region containing a uniform magnetic field directed into the figure (Figure 1), and then out to B=0
after point L. A current is induced in the loop
as it passes line J or line L.
A bar magnet is held above the floor and dropped (Figure 1). In case (a), the magnet falls through a wire loop. In case (b), there is nothing between the magnet and the floor. If there is induced current, wouldnt that cost energy? Where would that energy come from in case (a)?
there is less kinetic energy in case (a) than in case (b).
A nonconducting plastic hoop is held in a magnetic field that points out of the figure (Figure 1). As the strength of the field increases,…?
an induced emf will be produced but no current
A long straight wire carries a current I
as shown in (Figure 1). A small loop of wire rests in the plane of the figure. Which of the following will not induce a current in the loop?
moving the loop in a direction parallel to the wire
Two separate but nearby coils are mounted along the same axis. A power supply controls the flow of current in the first coil, and thus the magnetic field it produces. The second coil is connected only to an ammeter. The ammeter will indicate that a current is flowing in the second coil
only when the current in the first coil changes
When a generator is used to produce electric current, the resulting electric energy originates from which source?
whatever rotates the generator’s axle
Which of the following will not increase a generator’s voltage output?
rotating the magnetic field so that it is more closely parallel to the generator’s rotation axis
Which of the following can a transformer accomplish?
changing both current and voltage
A laptop computer’s charger unit converts 120 V from a wall power outlet to the lower voltage required by the laptop. Inside the charger’s plastic case is a diode or rectifier that changes ac to dc plus a
transformer
Which of the following statements about transformers is false?
transformers work using AC current or DC current
A 10- V, 1.0- A dc current is run through a step-up transformer that has 10 turns on the input side and 20 turns on the output side. what is the output?
0 V, 0 A
The alternating electric current at a wall outlet is most commonly produced by
a rotating coil that is immersed in a magnetic field
In a vacuum, what is the difference between a radio wave and an X-ray?
frequency, wavelength
The radius of an atom is on the order of 10^−10m. In comparison, the wavelength of visible light is…
much larger
Which of the following travel at the same speed as light?
infrared radiation, X-rays, gamma rays, microwaves, radar, cell phone signals, radio waves
Which of the following types of electromagnetic radiation travels the fastest?
ALL the above travel at the same speed
In empty space, which quantity is always larger for X-ray radiation than for a radio wave?
frequency
If electrons in a wire vibrate up and down 1000 times per second, they will create an electromagnetic wave having
a frequency of 1000Hz
If the Earth-Sun distance were doubled, the intensity of radiation from the Sun that reaches the Earth’s surface would
drop to 1/4
An electromagnetic wave is traveling straight down toward the center of the Earth. At a certain moment in time the electric field points west. In which direction does the magnetic field point at this moment?
North
If the intensity of an electromagnetic wave doubles,
both the magnetic field and the electric field must increase by a factor of square root of 2
If all else is the same, for which surface would the radiation pressure from light be the greatest?
a white surface
To watch today’s digital broadcast TV, could you use a pre-2009 TV antenna meant for analog? Explain.
yes; digital signals are broadcast with the same carrier frequencies, so your antenna will be fine
Starting in 2009, TV stations in the U.S. switched to digital signals. To watch today’s digital broadcast TV, could you use a pre-2009 TV antenna meant for analog? Explain.
Yes; digital signals are broadcast with the same carrier frequencies, so your old antenna will be fine.
A) Who will hear the voice of a singer first: a person in the balcony 53.5m away from the stage (Figure 1), or a person 1200km away at home whose ear is next to the radio listening to a live broadcast?
B) How much sooner? Assume that the microphone is a few centimeters from the singer and the temperature is 20 ∘C (speed of sound is 343 m/s).
A) person listening to the broadcast
B)?
Suppose you are standing about 3 m
in front of a mirror. You can see yourself just from the top of your head to your waist, where the bottom of the mirror cuts off the rest of your image. If you walk one step closer to the mirror…
you will not be able to see any more of your image
When the reflection of an object is seen in a flat mirror, the image is…
virtual and upright
You want to create a spotlight that will shine a bright beam of light with all of the light rays parallel to each other. You have a large concave spherical mirror and a small lightbulb. Where should you place the lightbulb?
at the focal point of the mirror
When you look at a fish in a still stream from the bank, the fish appears shallower than it really is due to refraction. From directly above, it appears…
shallower than its real depth
Parallel light rays cross interfaces from medium 1 into medium 2 and then into medium 3 as shown in (Figure 1). What can we say about the relative sizes of the indices of refraction of these media?
n2 > n1 > n3
To shoot a swimming fish with an intense light beam from a laser gun, you should aim…
directly at the image
When moonlight strikes the surface of a calm lake, what happens to this light?
some of it reflects back to the air; some enters the water
Light passing through a double-slit arrangement is viewed on a distant screen. The interference pattern observed on the screen would have the widest spaced fringes for the case of
red light and a small slit spacing
the colors in a rainbow are caused by
different amounts of refraction for light of different colors by the water in the raindrops
Which of the following statements is true regarding how blackbody radiation changes as the temperature of the radiating object increases?
The maximum intensity increases, and the peak wavelength decreases.
Which statement is true?
There are more photons in the blue beam.
There are more photons in the red beam.
Both beams contain the same number of photons.
The number of photons is not related to intensity.
There are more photons in the red beam.
What is the energy of photons (joules) emitted by an 90.9- MHz FM radio station?
(6.26x10^-34) x 90.9x10^6 = 6.023x10^-26
Calculate the ratio of the kinetic energy of an electron to that of a proton if their wavelengths are equal. Assume that the speeds are nonrelativistic.
(1.67x10^-27)/(9.1x10^-31) =
1835.16kg
Elements of the Periodic Table are distinguished by…
the number of protons in the nucleus
A nucleus has …
less energy than its component neutrons and protons have.
Which of the following will generally create a more stable nucleus?
having a larger binding energy per nucleon
The half-life of a radioactive nucleus is
the time it takes for half of the substance to decay.
Carbon dating is useful only for determining the age of objects less than about _____ years old.
60,000
Uranium-238 decays to lead-206 through a series of
some combination of alpha, beta, and gamma decays.
The Earth is several billion years old, so why do we still find radon on this planet?
Heavier unstable isotopes decay into it.
The 7:3Li nucleus has an excited state 0.48 MeV above the ground state.
2.6x10^-12 m
Estimate the total binding energy for 63:29Cu, using the figure.
550 MeV
