Physics Exam #3
An electric razor completes 60 cycles every second. What are (a) its frequency and (b) its period?
(a) 60 cycles per second or 60 hz (b) 1/60 second
How does the magnitude of electric force compare with the charge between a pair of charged particles when they are brought to half their original distance of separation? To one-quarter their original distance? To four times their original distance? (What law guides your answers?)
-half = 4 times (1/4th) -one-quarter = 1/16th -four times = 1/16th (1/4 distance = 4 times) Coloumbs Law
If you put in 10 J of work to push 1 C of charge against an electric field, what is its voltage with respect to its starting position? When you release it, what is its kinetic energy if it flies past its starting position?
10 J per Coulomb is 10 V. When released, its 10 J of potential energy will become 10 J of Kinetic energy as it passes its starting point
In a simple circuit consisting of a single lamp and a single battery, when the current in the lamp is 2 A, the current in the battery is
2 A
When a battery does 24 Joules of work on 10 Coulombs of charge, the voltage it supplies is _____.
2.4 V
When a 10-V battery is connected to a resistor, 2 A of current flow in the resistor. What is the resistor's value?
5 ohms
How much energy is given to each Coulomb of charge passing through a 6-V battery?
6 J
The underlying physics of an electric motor is that
A current-carrying wire experiences force in a magnetic field
Why doesn't a magnet pick up a penny or a piece of wood?
A penny and a piece of wood have no magnetic domains that can be induced into alignment.
What happens to the brightness of each lamp in a series circuit when more lamps are added to the circuit?
Adding more lamps in a series circuit produces a greater circuit resistance. This decreases the current in the circuit and therefore in each lamp, which causes dimming of the lamps. Energy is divided among more lamps, so the voltage drop across each lamp is less
When you thrust a bar magnet to and fro into a coil of wire, you induce
Alternating current
The loudness of a sound is most closely related to its
Amplitude
A sonic boom cannot be produced by
An aircraft flying slower than the speed of sound
"An electron always experiences a force in an electric field, but not always in a magnetic field." Defend this statement.
An electron always experiences a force in an electric field because that force depends on nothing more than the field strength and the charge. But the force an electron experiences in a magnetic field depends on an added factor: velocity.
Opposite charges_____.
Attract
Which statement is correct? (a) Voltage flows in a circuit (b) Charge flows in a circuit (c) A battery is the source of electrons in a circuit (d) All are correct
Charge flows in a circuit
The electrons in the wire are moving
Clockwise
When you double the voltage in a simple electric circuit, you double the
Current
What produces a magnetic field?
Electric charges in motion
Surrounding moving electric charges are
Electric fields and magnetic fields
What causes electric shock: current or voltage?
Electric shock occurs when current is produced in the body, but the current is caused by an impressed voltage
An object that has unequal numbers of electrons and protons is ___________.
Electrically charged
The essential physics concept in an electric generator is
Faraday's Law
When a pair of charged particles are brought twice as close to each other, the force between them becomes
Four times as strong
When a pair of charged particles are brought twice as close to each other, the force between them becomes _____.
Four times as strong
What happened to the current in the other lamps if one lamp in a series circuit burns out?
If one of the lamp filaments burns out, the path connecting the terminals of the voltage source breaks and current ceases. All lamps go out.
Two charged particles are projected into a magnetic field that is perpendicular to their velocities. If the charges are deflected in opposite directions, what does this tell you about the particles?
If the particles enter the field moving in the same direction and are deflected in opposite directions (say, one left and one right) the charges must be of opposite sign.
If a proton at a particular distance from a charged particle is repelled with a given force, by how much does the force decrease when the proton is three times as distant from the particle? Five times as distant?
In accord with the inverse-square law, at three times the distance, the force decreases to 1/9 its original value. At five times the distance, the force decreases to 1/25 of its original value.
The vibrations set up in a radio loudspeaker have the same frequencies as the vibrations
In the electric signal fed to the loudspeaker and that produce the sound you hear
Noise-canceling devices such as jackhammer earphones make use of sound
Interference
An object with zero net charge _____________.
Is always attracted to charged objects
To say that an object is electrically polarized is to say ________.
Its charge have been rearranged
Electricity and magnetism connect to form
Light
Beneath the complexities of electrical phenomena lies a fundamental rule from which nearly all other electrical effects stem. What is this fundamental rule?
Like charges repel; opposite charges attract
a 20 ohm resistor carries 10 Amperes. The voltage across the resistor is ________.
More than 10 Volts
In a circuit with two lamps in parallel, if the current in one lamp is 2 A, the current in the battery is
More than 2 A
When a 134 Hz tuning fork and a 144 Hz tuning fork are struck, the beat frequency is
More than 8 Hz.
If it has more electrons than protons, the object is _______.
Negatively charged
Electric potential and electric potential energy are _____.
Neither of these (one and the same in most cases, or two terms for the same concept)
When a light or sound source moves toward you, is there an increase or a decrease in the wave speed?
Neither! The frequency of a wave undergoes a change when the source is moving, not the wave speed
How is Coulomb's law similar to Newton's law of gravitation? How is it different?
Newton's law of gravitation is attractive, whereas Coulomb's law is attractive or repulsive. Both are proportional to the inverse square of distance.
What law of physics tells you that if a current-carrying wire produces a force on a magnet, a magnet must produce a force on a current carrying wire?
Newton's third law, which applies to all forces in nature
When we say charged is conserved, we mean that charge can
Not be created or destroyed
A magnetic force acting on a beam of electrons can change
Only in the direction of the beam
When we consider the time it takes for a pendulum to swing to and fro, we're talking about the pendulum's
Period
The vibrations along a transverse wave move in a direction
Perpendicular to the wave direction
What is the sign of charge of the particle in this case?
Positive
What kind of charge does an object acquire when electrons are stripped from it?
Positive charge.
If an object has fewer electrons than protons, it is ______.
Positively charged
How does the number of protons in the atomic nucleus normally compare with the number of electrons that orbit the nucleus?
Protons carry an amount of positive charge equal to the negative charge of electrons.
If you double both the current and the voltage in a circuit, the power
Quadruples
Like charges _____.
Repel
A common example of a longitudinal wave is
Sound
The speed of sound varies with
Sound and light
If the difference in height between the crest and trough of a wave is 60 cm, what is the amplitude of the wave?
The amplitude is 30 cm, half of the crest-to-trough height distance
How does an electrically polarized object differ from an electrically charged object?
The charge in an electrically charged object moves through the object. The charge in an electrically polarized object shifts its position inside of the molecules of the object and align themselves.
How does the charge of an electron differ from the charge of a proton?
The charges of the two particles are equal in magnitude but opposite sign.
The five thousand billion billion freely moving electrons in a penny repel one another. Why don't they fly out of the penny?
The electrons are attracted to the same number of protons in the penny.
The source of all magnetism is
The motion of electrons
The proton is the nucleus of the hydrogen atom, and it attracts the electron that orbits it. Relative to this force, does the electron attract the proton with less force, more force, or the same amount of force?
The same amount of force, in accord with Newton's third law-basic mechanics! Recall that a force is an interaction between two things-in this case, between the proton and the electron. They pull on each other equally.
Do compressions and rarefactions in a sound wave travel in the same direction or in opposite directions from one another?
They travel in the same direction.
A charge can only be _____________.
Transferred from one object to another
Charge flows in a circuit (T or F)
True
A step-up transformer in an electric circuit can step up
Voltage
If you scuff electrons onto your shoes while walking across a rug, are you negatively or positively charged?
When your rubber-or-plastic shoes drag across the rug, they pick up electrons from the rug in the same way you charge a rubber rod by rubbing it with a cloth. You have more electrons after you scuff your shoes, so you are negatively charged (and the rug is positively charged).
Does every magnet necessarily have a north and south pole?
Yes
We know that a compass points northward because Earth is a giant magnet. Does the northward-pointing needle point northward when the compass is brought to the southern hemisphere?
Yes, for the compass aligns with the Earth's magnetic field, which extends from the magnetic pole in the Southern Hemisphere to the magnetic pole in the Northern Hemisphere.
Is it possible for one wave to cancel another wave so that no amplitude remains?
Yes. This is called destructive interference. When a standing wave is set up in a rope, for example, parts of the rope have no amplitude- the nodes.
When you comb your hair, you scruff electrons from your hair onto the comb. Is your hair then positively or negatively charged? How about the comb?
Your hair will have a positive charge. The comb will have a negative charge.
A magnetic forces acts most strongly on a current-carrying wire when the wire
carriers a very large current and is perpendicular to the magnetic field
An electric field surrounds all
electric charges, electrons, and protons
2 lamps in parallel and 2 lamps in series all lamps have 2A passing through them. The battery for the series circuit is _______ the battery of the parallel circuit.
greater than
Voltage is applied _________.
through a circuit