Lines and Vectors
Field Equations
Fields trivia
Old school electrostatics
Other physics trivia
100
the blue sphere represents an electron. Both electrons are at an equal distance from the source. How do the forces exerted on the electrons compare?
The electron on the picture to the right will have more force exerted on it. The density of field lines represents the strength of the field. The field shown to the right is stronger, and therefore the electron will have more force exerted on it.
100
Fill in the blank for the following:
For a given source charge, electrical potential will_______ in magnitude with greater distance
decrease. The exact equation is V=kcQ/r
100
A line near a source charge where the potential at each point along the line is equal is....
an equipotential line
100
This quantity describes how hard a push or a pull is
Force
200
For the point in space, is the E field pointing left, right or zero? Explain. (both objects have the same magnitude of charge and the point is equidistant from both.
The contribution of both charged objects is to the left, so the E field overall is to the left at that point.
200
How will the magnitude of the E field change if separation from the source charge grows by a factor of 5?
The E field would become 25 times smaller. The equation is E=kcQ/r2
200
How are field lines drawn for the two kinds of charged objects?
they extend outward from a positively charged object, inward for a negatively charged object.
200
The law that describes the electric force objects exert on each other is....
Coulomb's Law
200
which of Newton's laws describes the relationship between the direction of force and the direction of an object's change in velocity?
Newton's First Law
300
the picture shows the charge distribution within a conductor. How will the charged objects rearranged themselves as a result of the presence of the external electric field?
the negatively charged free electrons will accelerate up, since negatively charged objects accelerate against the direction of the electric field.
300
three test charges surround a source charge at equal distances. Rank each charge in terms of most amount of force exerted to least.
The order is 3q, 2q, and q. The force a field exerts on a charge is FField on charge=Eq. The E field will have the same strength at the location of each charge since all are equally far apart from the source. However, the greater the magnitude of charge, the larger the force the field exerts.
300
Define what an electric field is
A region of "warped" space where charged objects will accelerate due to the presence of one or more source charges.
300
the sign of potential energy is ..... for like charges and .... for opposite charges
positive, negative
300
Two balls hit each other, but they accelerate differently. If objects exert equal amounts of force on each other, how can that be?
The objects will accelerate differently because they have different amounts of mass, but the force they exert on each other is the same.
400
The field lines shown above correspond to an infinitely long charged plate. Where is the plate located, relative to point A, if the plate is negatively charged? If it's positively charged?
To the left of A if it's positively charged, to the right if it's negative charged.
400
Points A, B, and C are some distance away from a source charge(each point is empty). Rank the points in the order of least potential ENERGY to most potential ENERGY
A=B=C
Uq is 0J for all points, since Uq depends on the presence of at least two charged objects.
400
Make a choice and explain:
Two identical positive charges are located at a distance d from each other. Where are both the E field and the electric potential zero?
(a) exactly between the charges
(b) at a distance d from both charges (all three points make a triangle)
(c) both a and b can work
(d) none of the choices are correct.
(d) is the answer. Since each charge is positive, and potential(V) is a scaler, the potential will never add to 0V for two like charges.
400
summarize the main differences between conductors and insulators
Both are attracted to charged objects while neutral
neutral conductors experience greater attraction
conductors have free electrons
insulators have their electron's bound to their atoms/molecules
400
Name 4 vector quantities(if you name a single scalar, you lose)
position
displacement
velocity
acceleration
force
E field
500
The picture shows equipotential lines. Indicate the direction of acceleration for the two charged objects
A positively charged object will move towards a region of lower potential, so it would accelerate to the right(towards -50V). The opposite is true for the negatively charged object, which accelerates left.
500
The pictures above show two fields, both of which are uniform. Rank in the order of least to greatest: potential difference between: A and B, C and D, and F and G. The separation between each pair is the same.
Ranking: The ranking is C and D, A and B, C and D.
The equipotential lines are perpendicular to the field lines, so for there to be a potential difference between two points, there must be some horizontal separation. Since potential difference also depends on the magnitude of the E field, for a given separation, the potential difference will be larger for a stronger E field. C and D fall along the same equipotential, and the potential difference between them is 0V. While A and B and F and G have the same separation, the E field is stronger near F and G, and therefore the potential difference between the two points is greater and magnitude than the potential difference between A and B
500
Jim says "the direction of the field lines is the direction in which a charged object will move". Explain if he's right or wrong
Jim is incorrect. Movement is based on an objects velocity. Field lines represent the direction in which + charged object accelerates
500
A positively charged balloon is attracted to a neutral metal wall. Will the system's electrical potential energy be negative or positive?
Negative is the answer.
500
A skater moving in a circular path at constant speed, and travels from one end of the circle to another while being pulled by a rope. The work done by the rope is
a. positive
b. negative
c. 0J
d. need more information
the answer is 0J. The force the rope exerts doesn't make the person gain or lose speed, and also does not elevate them. Therefore, the skater's total energy remains unchanged.