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
