Fundamentals of Electric Charge - AP Physics 1
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Two charges of 
and 
are placed 
away from each other. Another charge is placed in between these two charges. Where should this third charge be placed in order for it to feel no net electrostatic force?
Two charges of
The electrostatic force between two charges is:
The force that the 3rd charge feels from the 
charge is:
The force that the 3rd charge feels from the 
charge is:
We can also rewrite the distance between the charges as 
and 
. In this explanation, we will use 
as the distance between the 
and the third unknown charge making the distance between the 
and the 3rd charge 
. Finally, we solve for a net force of 0 giving us this relationship between the two opposing forces.
Solve for 
.
The electrostatic force between two charges is:
The force that the 3rd charge feels from the
The force that the 3rd charge feels from the
We can also rewrite the distance between the charges as
Solve for
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A point charge of charge 
is placed in a uniform electric field of strength 
going to the right. The charge is then moved 
at an angle of 
below the horizontal to the right. What is the net work done on this charge?
A point charge of charge
The work done by an electric field on a charged particle is:
Where 
is the angle between the electric field vector and the displacement vector. Plug in the given values.
This answer makes sense since an electric field does work on a positive charge when going in the direction of the field lines.
The work done by an electric field on a charged particle is:
Where
This answer makes sense since an electric field does work on a positive charge when going in the direction of the field lines.
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A student has a neutrally charged glass rod and a neutrally charged silk cloth. When the student rubs the silk cloth on the glass rod, the rod acquires a net positive charge. What is the charge on the silk cloth after the student performs this experiment?
A student has a neutrally charged glass rod and a neutrally charged silk cloth. When the student rubs the silk cloth on the glass rod, the rod acquires a net positive charge. What is the charge on the silk cloth after the student performs this experiment?
Charge is fundamentally conserved. In order to give the glass rod a positive charge, the silk cloth removes electrons from the glass rod. Every electron that leaves the glass rod leaves behind the proton (positively charged particle) that used to balance the negative charge of the electron (negatively charged particle). Every electron that leaves the glass rod goes onto the silk cloth, giving it the same amount of charge as the glass rod, but with a negative sign (since electrons are negatively charged). Only a tiny fraction of the total electrons in the glass rod are removed, even with vigorous charging.
Charge is fundamentally conserved. In order to give the glass rod a positive charge, the silk cloth removes electrons from the glass rod. Every electron that leaves the glass rod leaves behind the proton (positively charged particle) that used to balance the negative charge of the electron (negatively charged particle). Every electron that leaves the glass rod goes onto the silk cloth, giving it the same amount of charge as the glass rod, but with a negative sign (since electrons are negatively charged). Only a tiny fraction of the total electrons in the glass rod are removed, even with vigorous charging.
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If the test charge is increased by a factor of 4, what happens to the electric potential of that charge?
If the test charge is increased by a factor of 4, what happens to the electric potential of that charge?
Remember that the formula for the electric potential is given by:
Where 
is Coulomb's constant, 
is the source charge, and 
is the distance. This formula indicates that electric potential is unaffected by changing the test charge.
Remember that the formula for the electric potential is given by:
Where
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By how much will the electric field change if the charges of all source charges are increased by a factor of 
, and the test charge is increased by a factor of 
?
By how much will the electric field change if the charges of all source charges are increased by a factor of
The electric field 
for point charges is given by:
Where 
is Coulomb's constant, 
is the charge of each source charge ,
is distance of the test charge from the source charge, and 
is the number of source charges.
In this problem, since all of the source charges are increased by a factor of 2, the electric field will also increase by a factor of 2. The increase in the charge of the test charge is not applied to the strength of the electric field, since the electric field is only dependent on the values and locations of the source charges.
The electric field
Where
In this problem, since all of the source charges are increased by a factor of 2, the electric field will also increase by a factor of 2. The increase in the charge of the test charge is not applied to the strength of the electric field, since the electric field is only dependent on the values and locations of the source charges.
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Two identical conducting spheres are attached to insulated posts and charged so that 
and 
.
The spheres are brought together so they touch, then moved back apart. What is the charge on 
now?
Two identical conducting spheres are attached to insulated posts and charged so that
The spheres are brought together so they touch, then moved back apart. What is the charge on
When the spheres make contact, charges are exchanged. The charges on the spheres will move due to the Coulomb forces from all the particles in each sphere. They will move toward equilibrium.
In this case 
has a net negative charge while 
has a net positive charge. 
will have to migrate to 
so that 
.
When the spheres are separated they will have equal charge and the charge on 
will still be 
.
When the spheres make contact, charges are exchanged. The charges on the spheres will move due to the Coulomb forces from all the particles in each sphere. They will move toward equilibrium.
In this case
When the spheres are separated they will have equal charge and the charge on
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Determine the total electric charge of 
molecules in solution in Coulombs.
Determine the total electric charge of
In solution, the ions will disassociate into 
and 
. Since there will be 
molecules of 
with a total charge 
and 
molecules of 
with a total charge of 
, the overall charge will be 
In solution, the ions will disassociate into
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Consider the given diagram of two electrical charges. Which of the following is true about charges A and B?
Consider the given diagram of two electrical charges. Which of the following is true about charges A and B?
In this question, we're presented with a diagram in which two electrical charges have field lines pointing away from them. We're then asked to determine a true statement regarding these two charges.
To be able to answer this question correctly, we'll have to recall that for positive electrical charges, the field lines will always point away from the charge. For negative electrical charges, the field lines point inwards toward the charge. Since both charges A and B in the diagram have their field lines pointing away from them, both of them must be positively charged. Also notice that their field lines will not cross one another; instead, they are repelled from one another.
In this question, we're presented with a diagram in which two electrical charges have field lines pointing away from them. We're then asked to determine a true statement regarding these two charges.
To be able to answer this question correctly, we'll have to recall that for positive electrical charges, the field lines will always point away from the charge. For negative electrical charges, the field lines point inwards toward the charge. Since both charges A and B in the diagram have their field lines pointing away from them, both of them must be positively charged. Also notice that their field lines will not cross one another; instead, they are repelled from one another.
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An electric field line is point from the left towards the right. Where will an electron move when placed in the field?
An electric field line is point from the left towards the right. Where will an electron move when placed in the field?
The electron will move towards the left because electric field lines always point towards the negative charge. The electron is negatively charged and will oppose the negative electric field on the right and move towards the positive end on the left.
Therefore the correct answer is that the electron will move to the left.
The electron will move towards the left because electric field lines always point towards the negative charge. The electron is negatively charged and will oppose the negative electric field on the right and move towards the positive end on the left.
Therefore the correct answer is that the electron will move to the left.
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A point charge of 
coulombs experiences a force of 
in an electric field. What is the magnitude of this electric field?
A point charge of
The formula for the force on a point charge in an electric field is as follows:
is the force on the charge, 
is the magnitude of the charge and 
is the electric field. Substituting for our values we obtain:
Therefore the correct answer is 
The formula for the force on a point charge in an electric field is as follows:
Therefore the correct answer is
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