High School Physics : Electric Force
Study concepts, example questions & explanations for High School Physics
Example Questions
Example Question #1 :Electric Force
A large electroscope is made with “leaves” that are
Each of these charged spheres exert a force on each that is equal and opposite on one another in the x-direction. The tension force on each of these charged spheres is equal to the force from the other sphere in the x-direction and the force of gravity in the y-direction. We will be able to use this information to determine the charge on the electroscope.
First we must analyze the forces on the charges and determine the force on the charges. We know that
Rearranging this we get
Next we can use Coulomb’s law to determine the magnitude of each charge.
In order to figure out the distance between the two spheres we can trigonometry with the length of the string.
Therefore the distance between the two charges is double this value.
Example Question #932 :High School Physics
Two charges -Q and -3Q are a distance l apart. These two charges are free to move but do not because there is a third(fixed) charge nearby. What must the magnitude of the third charge and its placement be in order for the first two to be in equilibrium.
The charge must be placed
The charge must be placed
The charge must be placed
The charge must be placed
The charge must be placed
First let us determine the force of the two charges on each other.
The easiest way to analyze this is to assume all of these are in a straight line and we have a charged placed somewhere along the same x-axis between the charges that keeps them all from moving. Let us assume the smaller charge is at the origin and the distance to the fixed charge is some distance
Let us also assume that the larger charge is a distance l away from the origin (away from the smaller charge) and therefore a distanc l-r away from the fixed charge.
To be in equilibrium we know that the net force on the smaller charge must equal
We also know that the net force on the larger charge must equal
We can set these two equations equal to each other.
The force between the charges can be cancelled since it is on both sides.
The k and Q values can also be cancelled out on both sides.
Cross multiply on both sides
This is a quadratic that needs to be solved with a quadratic formula.
So the two options for the
Of these two, the one that makes the most sense based on our assumptions is the
We can now go back to our first equation with the smaller charges
We can plug in our value for the
The
The charge must be placed
Example Question #933 :High School Physics
Particles of charges
We can calculate the force from each of the two charges on the center charge using Coulomb’s Law
The first charge on the middle charge
The last charge on the middle charge
To find the total force we need to add both of these forces together.
Example Question #934 :High School Physics
A point charge of +Q is placed at the center of a square. When a second point charge of -Q is placed at one of the square’s corners it is observed that an electrostatic force of 4N acts on the positive charge at the square’s center. Now, identical charges of -Q are placed at the other three corners of the square. What is the magnitude of the net electrostatic force acting on the positive charge at the center of the square?
Since the charges are opposite, the center charge +Q is going to be attracted to each of the charges in the corner of the square. Since each charge is equidistant from the center charge, they will each exert 4N of force on the charge in the center. However, since each corner charge is pulling the center charge equally and oppositely, the net force on the system is equal to 0 and the charge will not move. All of the forces cancel out with one another.
Example Question #931 :High School Physics
When the distance of two interacting charges is increased by a factor of 2, the electrical forces between these charges is __________.
doubled
reduced by a factor of 4
reduced by a factor of 3
reduced by a factor of 2–√
quadrupled
reduced by a factor of 4
在C语言中oulomb’s Law, an increase in the distance will cause a decrease in the magnitude of the electrical force between them. Since this is an example of an inverse square law, doubling the distance will reduce the force by a factor of 4.
Example Question #1 :Electric Force
What is the main difference between electrical and gravitational forces?
引力遵循平方反比定律nd electrical forces do not
Electrical forces obey the inverse square law and gravitational forces do not
Electrical forces attract and gravitational forces repel
Gravitational forces are always attractive but electrical forces can be attractive or repulsive
Gravitational forces are always attractive but electrical forces can be attractive or repulsive
Electric forces can be attractive or repulsive because charges may be positive or negative. In the case for gravitational forces, there are only attractive forces because mass is always positive.
Example Question #937 :High School Physics
What is the magnitude of force a
We can calculate this using Coulomb’s Law
Example Question #931 :High School Physics
当两个的大小interacting charges is increased by a factor of 2, the electrical forces between these charges is __________.
quadrupled
reduced by a factor of 2–√
reduced by a factor of 3
reduced by a factor of 4
doubled
quadrupled
在C语言中oulomb's law, an increase in both interacting charges will cause an increase in the magnitude of the electrical force between them. Specifically if the magnitude of both interacting charges is doubled, this will quadruple the electrical force.
Example Question #939 :High School Physics
At each corner of square of side
We will need to use Coulomb’s Law to analyze the force on the 3Q charge from all the other forces. We will then summarize the net force in the
In the x-direction
Force from 4Q on 3Q
Force from Q on 3Q in the x direction
Add these together in the x-direction
In the y-direction
From from 2Q on 3Q
Force from Q on 3Q in the y direction
Add these together in the y-direction
Now we can find the resultant of these sides using the Pythagorean theorem.
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