DSM Modules 21-27
Consider a conductor at rest in a static electric field. Which statement is true about how the conductor interacts with the electric field?
(These are all the true statements) 1. The electric field is perpendicular to the surface of the conductor at all points along its surface. 2. The electric field inside the conductor is exactly ZERO 3. Any net charge on the conductor resides on the surface of the conductor -Because the charges in the conductor are free to move around, the charges that reside on the surface of the conductor must be experiencing a field that is perpendicular to the surface of the conductor.
Which of the following is true about electric field lines due to static charge distributions?
(These are all true statements) 1. Electric field lines CANNOT cross 2. EFL are directed AWAY from (+) objects and toward (-) objects 3. Electric field lines will be more closely spaced from each other in regions where the electric field is stronger -Electric field is ALWAYS tangent to the electric field line at a given location. Having two lines cross would be a contradiction. -Electric field lines always begin on a positively charged object and end on a negatively charged object
A wire carries a current in the +x-direction. A positively charged particle moves in the -x-direction near the current-carrying wire. In what direction will the charged particle feel a magnetic force?
+y-direction
In the diagram below, in what direction will the magnetic force on the charged particle point at the moment the particle enters the uniform magnetic field? + --> v
+y-direction
In the diagram below, in what direction will the magnetic force on the charged particle point at the moment the particle enters the uniform magnetic field?
-x-direction
A 10 cm-long wire carrying a current of 2 A is immersed in a uniform magnetic field of 0.5 T. If the magnetic field is oriented perpendicular to the wire, what is the magnitude of the force that the wire will experience?
0.1N
A 30 cm-long wire carrying a current of 0.5 A is immersed in a uniform magnetic field of 4 T. If the magnetic field is oriented perpendicular to the wire, what is the magnitude of the force that the wire will experience?
0.6 N
A 20 cm-long wire carrying a current of 3 A is immersed in a uniform magnetic field of 3 T. If the magnetic field is oriented at an angle of 30° to the wire, what is the magnitude of the force that the wire will experience?
0.9 N
Consider the network of 4 resistors shown. Resistor A and resistor D are ______.
1. Neither in series nor in parallel with each other
Consider the simple arrangement of three resistors shown. Assume R sub A is greater than R sub B is greater than R sub C. The total equivalent resistance of the arrangement will be ______. (Figure A,B,&C are lined horizontally)
1. Smaller than the resistance of resistor C
Consider the circuit shown. When hooked up to a certain battery, there will be a current, I, moving to the right in the top wire (above resistor A). How would the current through resistor A compare to the current through resistor B plus the current through resistor C?
1. The current through resistor A will be the same as the current through resistor B plus the current through resistor C. Meaning IA = IB + IC.
The electric force on object B by object A is F. If the distance between the objects were tripled, but everything else was kept the same, what would be the new electric force on object B by object A?
1/9 F -The electric force between two objects is inversely proportional to the square of the distance between the centers of the two objects. -Increasing the distance by a factor of 3m causes the electric force to decrease by 9.
Suppose you have a single bar magnet. If you cut that bar magnet into 10 equal pieces, how many individual magnets would you end up with? What will the polarity of each piece of magnet look like?
10 individual magnets, each with a north and south pole
A solenoid has a net length of 2 m, a radius of 10 cm, and a current of 4 A running through it. The solenoid is comprised of 500 turns. What is the magnitude of the magnetic field in the solenoid?
1000 mu naught
An electron enters a uniform magnetic field of strength 0.25 T at 800 m/s. The magnetic field is oriented at an angle of 30° to the electron's velocity. What is the magnitude of the force that the electron experiences while it moves through the magnetic field?
100e
Two points, point A and point B, are situated above a current-carrying wire. Point B is located at a distance R from the wire, which is twice as far from the wire as point A. By what factor is the magnetic field at point A larger or smaller than the magnetic field at point B?
2
A coil of wire is comprised of 5 turns, has a current of 2 mA running through it, and a net magnetic field at its center of B is equal to start fraction mu naught over 40 end fraction times T. What is the radius of the coil of wire?
20 cm
An electron enters a uniform magnetic field of strength 0.5 T at 500 m/s. The magnetic field is oriented perpendicular to the electron's velocity. What is the magnitude of the force that the electron experiences while it moves through the magnetic field?
250e
The electric force between objects A and B is F. If the charge of object A were twice as large as it is, but everything else was kept the same, what would be the new electric force between objects A and B?
2F -Coulomb's law shows that the electric force between two objects is proportional to the charge of each object. If the charge of either object changes, the force that each object exerts on the other changes in the same way. -BOTH forces in the force-pair must be the SAME. so both are affected the same way.
A solenoid is comprised of 1,000 turns of wire and has a net current of 0.5 A running through it. Inside the solenoid is a magnetic field of 250 times mu naught. How long is the solenoid?
2m
You measure the magnetic field of a long, current-carrying wire to be B is equal to start fraction mu naught over 50 times pi end fraction at a distance of r = 7.5 cm. How much current is running through the wire?
3mA
A proton enters a uniform magnetic field of strength 0.5 T at 200 m/s. The magnetic field is oriented at an angle of 30° to the proton's velocity. What is the magnitude of the force that the proton experiences while it moves through the magnetic field?
50e
A proton enters a uniform magnetic field of strength 2 T at 300 m/s. The magnetic field is oriented perpendicular to the proton's velocity. What is the magnitude of the force that the proton experiences while it moves through the magnetic field?
600e
Four particles enter a uniform magnetic field that points into the page, as shown below. They each enter the magnetic field with the same velocity and each particle has the same mass. They do not, however, have the same charge. Which of the particles has the largest amount of charge on it?
A
Four particles enter a uniform magnetic field that points into the page, as shown below. They each enter the magnetic field with the same velocity, and each particle has the same charge. They do not, however, have the same mass. Which of the particles has the least amount of mass?
A
Individual electrons have a magnetic moment. In effect, they are very small magnets. In order for a ferromagnetic material to become magnetized, these electrons must do what with their magnetic moments?
Align their magnetic moments
Which is the best definition of an electric dipole?
An electric dipole is an arrangement of electric charge with two equal but opposite amounts of charge separated by some fixed distance. -It is important that the two charges be the same amount of charge, but have opposite signs. -Opposite but UNEQUAL charges CANNOT be considered a dipole, thought they can be considered a combination of a dipole and a point charge.
How do you calculate the electric force by object A exerted on object A (itself)?
An object never experiences an electric force due to itself.
Oxygen is the element that has 8 protons in its nucleus. If you start out with a neutral oxygen atom and it then loses 2 electrons, what is a good way to describe the resulting object?
An oxygen ion with a charge of +2e - "+3 ion" or a "+3e ion" means it has lost 3 electrons -Changing the number of electrons does not change the atom. Solely defined by the number of protons in the nucleus.
Which of the following ways can you use to make a permanent magnet? (Choose one.)
Apply a magnetic field to something ferromagnetic
Two long, parallel wires each carry the same current, I, and the two currents are parallel to each other. The two wires are a distance r apart. What is the magnitude of the magnetic field, B, at point P, the midpoint between the two wires?
B = 0 T, no direction because the fields cancel
The diagram below shows a long wire with a current of 2 A running through it that is going into the page. What would be the magnitude and direction of the associated magnetic field 4 cm away?
B = 25 times mu naught over pi, clockwise
Two long, parallel wires each carry the same current, I, but the two currents are anti-parallel. The two wires are a distance r apart. What is the magnitude and direction of the magnetic field, B, at a point that is at the midpoint, P, between the two wires?
B is equal to start fraction 2 times mu naught times I over pi times r end fraction, out of the page
The diagram below shows a long wire with a current of 5 A running through it that is coming out of the page. What would be the magnitude and direction of the associated magnetic field 5 cm away? Note that when calculating the direction, you will find that only one of the diagrams is correct.
B is equal to start fraction 50 times mu naught over pi end fraction, counter-clockwise
Two objects, each with a charge of +1 nC, are sitting alone in space. If we measure the magnitude of the electric field at a location given by vector r, which is equidistant from both objects, what result would we get?
Between E is equal to 0 and E is equal to 1/(4 times pi e0) times (2nC / r squared) -The electric field each object produces is a vector, the total electric field is the sum of those vectors. -the electric field will be zero in a point midway between the two charges and twice the magnitude in a point far away from both charges
Consider two point charges, A and B, separated by a distance, d. How would we find the total electric potential energy of this arrangement?
Calculate one electric potential energy for the pair.
An individual electron can be thought of as a spinning sphere of negative charge. A charged spinning sphere will generate a magnetic field, whose direction is indicated by the magnetic moment of the object, vector mu. In what direction will the electron rotate, based on the direction of its magnetic moment and the direction of the uniform magnetic field that it is immersed in?
Clockwise
The simplest atomic nucleus in nature is molecular formula of hydrogen, which consists of a single proton. Individual protons have charge and can be thought of as small spinning spheres. A charged spinning sphere will generate a magnetic field, whose direction is indicated by the magnetic moment of the object, vector mu. In what direction will the proton rotate, based on the direction of its magnetic moment and the direction of the uniform magnetic field that it is immersed in?
Clockwise
Current is defined (mathematically) by the equation I is equal to start fraction delta Q over delta t end fraction (for average current) or I is equal to start fraction dQ over dt end fraction (for instantaneous current, using calculus). Using whichever definition you are comfortable with, when considering current in a wire, this can be stated (conceptually) as which of the following?
Current is the rate at which charge passes a certain place in the wire.
Four particles enter a uniform magnetic field that points into the page, as shown below. They each enter the magnetic field with the same velocity, and each particle has the same charge. They do not, however, have the same mass. Which of the particles has the greatest mass?
D
Four particles enter a uniform magnetic field that points into the page, as shown below. They each enter the magnetic field with the same velocity, and each particle has the same mass. They do not, however, have the same charge. Which of the particles has the least amount of charge on it?
D
An object with a charge of +4 μC is very close to an object with a charge of -1 μC, each one fixed in place. Which of the following is the best expression for the magnitude of the electric field we would find at a distance vector r far away from the pair of objects?
E= 1/4pi e0 time (+3μC)/r2 -Because we are far away from the pair of objects, it is their net charge that matters most in determining the electric field. A good approximation is therefore to treat them as a single point charge with a net charge of +3 μC.
How are electric field lines related to equipotential surfaces?
Electric field lines are always perpendicular to equipotential surfaces and point toward locations of lower potential.
Suppose object A is electrically charged and is experiencing forces from three other charged objects. How should the total effects of those three objects be combined in order to find the total electric force?
Electric force vectors are calculated for object A and each of the other three objects. These three force vectors are then added using vector addition to obtain the total electric force. -Principle of superposition: applies to forces of all kinds. The net force on an object can always be found by using vector addition to add up all the forces that it experiences from other objects.
Which of these is a good description of the difference between electric potential energy and electric potential?
Electric potential energy is a property of a system of multiple charges while electric potential is a property of a location in space near a charge distribution.
Consider three point charges, A, B, and C, arranged in an equilateral triangle, with distance d on each side. How would we find the total electric potential energy of this arrangement?
Find the three electric potential energies (one for each pair) and add them up.
Suppose an object starts out electrically neutral. Through some process, 11 electrons are removed from the object. What is the electric charge of the object afterward?
Has the same net charge as 11 protons -Removing 11 electrons means there are now 11 protons whose charge is "unbalanced". This leaves the object with a net charge equal to 11 proton charges.
Circuit diagrams are almost always drawn with the assumption that the wires shown are "ideal wires." What is the "ideal wire" approximation?
Ideal wires refer to the wires we draw in a circuit diagram and have no resistance, and therefore have the same electric potential at all points on the wire.
Consider the network of 4 resistors shown. Resistor A and resistor B are ______.
In parallel with each other
Consider the network of 4 resistors shown. Resistor C and resistor D are ______.
In series with each other
Consider the simple arrangement of three resistors shown. Resistor A and resistor C are ______.
In series with each other
At the atomic level, what must happen in order for a ferromagnetic material to become magnetized?
Individual atomic magnetic moments need to align.
In the diagram, a conducting loop has a current running through it counter-clockwise. In which direction is the magnetic field outside of the loop going to be pointing?
Into the page
When an electric current passes through a light bulb, what happens to the current?
It is unchanged after passing through the lightbulb
A current-carrying solenoid is immersed in a uniform magnetic field, as shown in the diagram below. How will the current-carrying solenoid reorient itself, relative to the magnetic field?
It will rotate counter-clockwise, aligning its magnetic moment with the magnetic field.
A simple bar magnet is immersed in a uniform magnetic field, as shown in the diagram below. How will the bar magnet reorient itself, relative to the magnetic field?
It will rotate counter-clockwise, pointing its North end in the +x-direction.
Consider the simple arrangement of three resistors shown. Assume R sub A is greater than R sub B is greater than R sub C. The total equivalent resistance of the arrangement will be ______. (A,B,&C are lined vertically)
Larger than the resistance of resistor A
If a composite object is positively charged that means it
Must be either made entirely from positively charged objects or made from objects that have more total positive charge than negative charge -Determining the net charge that an object has is a matter of adding up the total charge of all its constituents.
A charged particle is immersed in a uniform magnetic field coming out of the page and is moving along a circular path in the counter-clockwise direction. What is the charge of the particle in this situation?
Negative
A charged particle is immersed in a uniform magnetic field going into the page and is moving along a circular path in the clockwise direction. What is the charge of the particle in this situation?
Negative
Consider the network of 4 resistors shown. Resistor B and resistor C are ______.
Neither in series nor in parallel with each other
If there is a system with a proton and an electron, can the electric potential energy of the system be exactly zero?
No, it will be negative no matter how they are arranged.
If there is a system with two electrons, can the electric potential energy of the system be exactly zero
No, it will be positive no matter how they are arranged.
Objects A and B are electrically repelled from each other. Can we tell what sign the charge of object A is?
No, we cannot tell.
Consider an idealized circuit diagram showing various elements (ideal resistors, ideal batteries, ideal wires, ideal capacitors, etc.). Which elements in the circuit obey Ohm's law, delta V is equal to I times R?
Only the resistors
A charged particle is immersed in a uniform magnetic field going into the page and is moving along a circular path in the counter-clockwise direction. What is the charge of the particle in this situation?
Positive
Consider a point with a large electric field. Are there differences in how positively and negatively charged objects are affected by this electric field?
Positively and negatively charged objects both experience equal magnitude forces due to the electric field, but in opposite directions -The underlying physics doesn't favor one type of charge over another. The only difference in how the two charge types are affected is that they are pushed in opposite directions by an electric field.
Suppose you have two identical resistors with resistance R. If you combine them in parallel, what will the total equivalent resistance be?
R sub eq = R/2
Suppose you have two identical resistors with resistance R. If you combine them in series, what will the total equivalent resistance be?
R sub eq is equal to 2 times R
Suppose you have a network of resistors with a total resistance R sub eq is equal to R sub I. If you hook up one more small resistor (compared to R sub i) in parallel with the original network, what would happen to the overall equivalent resistance?
R sub eq will decrease a large amount
Suppose you have a network of resistors with a total resistance R sub eq is equal to R sub I. If you hook up one more small resistor (compared to R sub i) in series with the original network, what would happen to the overall equivalent resistance?
R sub eq will increase a small amount.
A few different circuit elements (batteries, resistors, capacitors, etc.) are connected in series. What do all of them have in common?
The current through each one is the same.
Consider the circuit shown. When hooked up to a certain battery, there will be a current, I, moving to the right in the top wire (above resistor A). How would the current through resistor A compare to the current through resistor B?
The current through resistor A will be larger than the current through resistor B.
Consider the circuit shown. When hooked up to a certain battery, there will be a current, I, moving to the right in the top wire (above resistor A). How would the current through resistor A compare to the current through the bottom section of wire between the points marked n and m?
The current through resistor A will be the same as the current through the bottom wire.
Consider an electric dipole, composed of charges +q and -q separated by distance d, that is viewed from a large distance (large compared to d). What do we expect about the electric field due to the dipole viewed from this distance?
The electric field is significantly weaker than the electric field due to a single point charge q viewed from the same distance. -At a large distance the dipole will cancel each other out resulting in a weaker net field -However won't be ZERO. Each part of the dipole cannot exactly cancel out.
Suppose object A is experiencing an electric field with a magnitude of E at its location. If the charge on object A is doubled, what happens to the electric field it is experiencing?
The electric field that object A experiences is unchanged. -The electric field at a given location does not depend on the object. -Doubling the amount of A causes A to experience a larger force due to its interaction with the electric field but it own't change anything about the electric field at that location
Which of the following is a good description of the electric force between stationary charged objects?
The electric force between stationary charged objects is a conservative force for which there is a corresponding potential energy.
If a proton is moved a certain distance directly opposite an external electric field, what can we say about the change in the electric potential energy of the system?
The electric potential energy of the system will increase.
An arbitrarily shaped piece of conductor is given a net negative charge and is alone in space. What can we say about the electric potential within the conductor? Assume that the electric potential is zero at points that are very far away from the conductor.
The electric potential in the conductor will be negative and constant throughout the conductor.
An arbitrarily shaped piece of conductor is given a net positive charge and is alone in space. What can we say about the electric potential within the conductor? Assume that the electric potential is zero at points that are very far away from the conductor.
The electric potential in the conductor will be positive and constant throughout the conductor.
If a proton is moved a certain distance directly opposite an external electric field, what can we say about the change in the electric potential it experiences?
The electric potential it experiences will increase.
If an electron is moved a certain distance directly opposite an external electric field, what can we say about the change in the electric potential it experiences?
The electric potential it experiences will increase.
Consider an electric current, I, travelling through a circuit when it encounters a junction, splits into two branches A and B, and later rejoins back together. What parameter(s) are involved in determining the fraction of the original current, I, that travels path B?
The equivalent resistance of each of the branches are the determining factors.
How will the field strength in the solenoid be affected, if the number of loops in a solenoid is decreased by a factor of 4?
The field strength will be decreased by a factor of 4.
How will the magnetic field strength found inside of a solenoid be changed if the length of the solenoid is decreased by a factor of 5?
The field strength will be increased by a factor of 5.
How will the magnetic field inside of a coil of wire be changed if the radius of the coil is decreased by a factor of 10?
The magnetic field strength will increase by a factor of 10.
The diagram below is a close-up view of a material, showing the atomic magnetic moments associated with the atoms that make up the material. Based on the relative orientations of these atomic magnetic moments, what can you say about the material?
The material is magnetized (If arrows are pointing in the same direction) The material is NOT magnetized (if the arrows are basically pointing every direction)
If an object with charge -3 nC moves from a location that has a potential of -20 V to a location with a potential of -10 V, what has happened to the potential energy of the system?
The potential energy of the system has decreased by DELTA U= - (10V)(3nC)
If an object with charge +2 nC moves from a location that has a potential of 20 V to a location with a potential of -10 V, what has happened to the potential energy of the system?
The potential energy of the system has decreased by DELTA U= -(30V)(2nC)
Consider an electric current travelling across a series of two resistors A and B, experiencing a total voltage drop of delta V. What parameter(s) are involved in determining what fraction of the total voltage drop will be experienced by resistor A?
The resistance of both resistors are the determining factors.
A few different circuit elements (batteries, resistors, capacitors, etc.) are connected so that all of them are in parallel. What do all of them have in common?
The voltage across each one is the same.
A cube of copper and a sphere of aluminum are both positively charged and connected by a wire. What do the two conductors have in common?
They both have the same electric potential.
Two current-carrying wires are oriented parallel to each other, as shown in the diagram below. Both of the wires carry a current in the +x-direction. Keeping in mind that current-carrying wires always have an associated magnetic field, how will these two wires interact?
They will attract each other.
Two current-carrying wires are oriented parallel to each other, as shown in the diagram below. One of the wires carries a current in the +x-direction, the other carries a current in the -x-direction. Keeping in mind that current-carrying wires always have an associated magnetic field, how will these two wires interact?
They will repel each other
A current-carrying coil and a bar magnet are brought near one another, as shown in the diagram below. Keeping in mind that current-carrying wires always have an associated magnetic field, how will the current-carrying coil and bar magnet interact?
They will repel one another.(Bar magnet is on the left side) They will attract one another (Bar magnet is on the right side)
Taking note of the direction of the flow of current in the solenoid, in what direction does the solenoid's magnetic field point?
To the left
When two electrons are 1 cm apart, what expression could represent their electric potential energy?
U = 1/4pi e0 times (the absolute value of qe)2/ 0.01m
Within a ferromagnetic material, there are small regions called magnetic domains. What is responsible for the creation of these magnetic domains?
Unpaired electrons, each with a net magnetic moment, aligning
Consider a point 1 cm away from an electron with nothing else nearby. What expression could represent the electric potential at that location?
V= - 1/4pi e0 times the absolute value of qe / 0.01m
Real wires are made from "ohmic" materials, meaning they have some amount of resistance and obey Ohm's law. If we want to account for this in a circuit diagram, how do we do so?
We include additional resistors representing the resistance of the wire and then treat the wires in the diagram as ideal wires
Can there be a non-zero electric field at a point in space where no charged object is present? Can there be an electric field equal to zero at a point where a charged object is present?
Yes to both -Electric field can have any value (zero or non-zero) independent of whatever object is placed there.
The diagram below shows a close-up view of a material's magnetic domains. A small magnet is brought near the material, but only some of the domains have aligned with the permanent magnet's field. Is this a reasonable result?
Yes, because a very strong magnetic field is required to align all of the magnetic domains.
Consider the following statement: "If you connect another resistor to an existing network of resistors, the total equivalent resistance will decrease." Is this true?
Yes, but only if the new resistor is connected in parallel with the existing network.
Consider the following statement: "If you connect another resistor to an existing network of resistors, the total equivalent resistance will increase." Is this true?
Yes, but only if the new resistor is connected in series with the existing network
If there is a system with two electrons and a proton, can the electric potential energy of the system be exactly zero?
Yes, it could be zero if they were arranged properly.
If a composite object is electrically neutral, that means it
can be made from objects that each have zero electrical charge, or made from charged objects with equal amounts of total positive and negative charge - Electrically neutral objects MUST have a total net charge of zero.
An individual electron can be thought of as a spinning sphere of negative charge. A charged spinning sphere will generate a magnetic field, whose direction is indicated by the magnetic moment of the object, vector mu. In what direction will the electron rotate, based on the direction of its magnetic moment and the direction of the uniform magnetic field that it is immersed in?
clockwise
Every point on an equipotential surface ______.
has the same electric potential
If an electron is moved a certain distance directly opposite an external electric field, what can we say about the change in the electric potential energy of the system?
he electric potential energy of the system will decrease
In the diagram, a conducting loop has a current running through it clockwise. In which direction is the magnetic field inside the loop going to be pointing?
into the page
If an electron is moved in a direction perpendicular to an equipotential surface, ______.
it will be moving either in the same or exactly opposite direction as the electric field at that location
A coil of wire is made of 10 turns, has a radius of 4 cm, and a length of 2 mm. If the current running through this coil is 2 mA, what will be the magnitude of the magnetic field?
mu naught over 4 - B= u0NI / 2R B= u0(10 turns)(2mA)/2(0.04)
One similarity between protons and electrons is
protons and electrons have the same amount of charge, but protons have positive charge, while electrons have negative charge
When an electron approaches a positively charged nucleus, ______.
the electric potential energy of the system decreases while the potential at the electrons location increases
As we consider various points that are all on the same equipotential surface near some distribution of charge, ______.
the electric potential is the same at every point
As we consider various points that are all on the same equipotential surface near some distribution of charge
the electric potential is the same at every point, but the electric potential energy is different at every point
If an electron moves in a direction perpendicular to an equipotential surface, ______.
the potential it experiences must change