College Physics : College Physics
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Example Questions
Example Question #2 : Electromagnetics, Waves, And Optics
A light ray is traveling through air hits a transparent material at an angle of 
This problem requires Snell's Law and the corresponding equation:
We know that the index of refraction of air is:
We also know that:
Now we can plug in these values into the Snell's Law equation to find the index of refraction for the transparent material.
Finally, we need to calculate the speed of light moving through this transparent material now that we know the index of refraction for it. To do that, we need to use this equation:
Where 
Example Question #1 : Magnetism
Suppose that a magnetic field is oriented such that it is pointing directly to the left, as in the picture shown below. If a positively charged particle were to begin traveling through this magnetic field to the right, in which direction would the particle's trajectory begin to curve?
The particle would continue to move to the right unaffected
The particle would move out of the page
The particle would move into the page
The particle would move down the page
The particle would continue to move to the right unaffected
In order to answer this question, it's important to understand the factors that determine the magnetic force experienced by a charge. We can begin by writing out the equation for magnetic force.
As shown in the above equation, the magnetic force is directly proportional to the particle's charge, its velocity, and the strength of the magnetic field itself. But, for the purposes of the this question, the most important factor is the angle of the particle's velocity with respect to the magnetic field.
Notice that if theta is equal to zero, then the sine of theta will be equal to zero as well. This, in turn, will cause the magnetic force to also be zero. This is also true if we were to define theta as 
Since the particle is moving in a direction that is parallel to the magnetic field lines but in the opposite direction, we have a situation in which theta is equal to 
Example Question #1 : Magnetism
A single string of wire has a resistance of 
So this is all about the magnetic field strength around a current carrying wire.
The equation for this is:
But you must use Ohm's Law 
Since the wire has 
Being sure to change 
Example Question #1 : Electromagnetics
A charged particle traveling along the +x axis enters an electric field directed vertically upward along the +y-axis. If the charged particle experiences a force downward because of this field, what is the sign of the charge on this particle?
It is negative
It is positive
None of these
It is neutral
It is negative
Positive charges in an electric field will experience an electric force that is in the same direction as the electric field. If the charge is negative, the force will be in the opposite direction of the electric field. Since the charged particle experiences a force which is opposite to the electric field, the sign of the charge must be negative.
Example Question #1 : Electrostatics
When the magnitude of two interacting charges is increased by a factor of 2, the electrical forces between these charges is __________.
doubled
quadrupled
reduced by a factor of
reduced by a factor of 4
reduced by a factor of 3
quadrupled
In Coloumb'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 #2 : Coulomb's Law
What is the main difference between electrical and gravitational forces?
Gravitational forces obey the inverse square law and electrical forces do not
Electrical forces attract and gravitational forces repel
Electrical forces obey the inverse square law and gravitational forces do not
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 #3 : Coulomb's Law
Three equal charges are at three of the corners of a square of side d. A fourth charge of equal magnitude is at the center of the square as shown in Figure above. Which of the arrows shown represents the net force acting on the charge at the center of the square?
A
B
D
C
B
Because of the principles of superposition, each electric force that acts from the charges at the corners on to the charge at the center can be broken into components. Since all the charges are positive, all the forces will be repulsive. The forces acting from the top left and bottom right corners will cancel, leaving only the repulsive force coming from the bottom left corner.
Example Question #4 : Coulomb's Law
An electron traveling along the +x-axis enters an electric field that is directed vertically down, i.e., along the negative y-axis. What will be the direction of the electric force acting on the electron after entering the electric field?
Into the page
Upward
Out of the page
To the right
Upward
Positive charges in an electric field will experience an electric force that is in the same direction as the electric field. If the charge is negative, the force will be in the opposite direction of the electric field. Since we are talking about an electron moving in an electric field that points in the negative y-direction, the electron will feel a force that points in the positive y-direction, or upwards.
Example Question #2 : Electrostatics
A charged rod carrying a negative charge is brought near two spheres that are in contact with each other but insulated from the ground. If the two spheres are then separated, what kind of charge will be on the spheres?
The sphere near the charged rod becomes positive and the other becomes negative
The sphere near the charged rod becomes negative and the other becomes positive
None of these
The spheres do not get any charge
The sphere near the charged rod becomes positive and the other becomes negative
When the negatively charged rod is brought near one of the two spheres, the presents of the negative charge will induce a flow of charge in the spheres such that regions farthest away from the charged rod will become most negative and regions near the rod will become most positive. This is called charge by induction.
Example Question #3 : Electrostatics
By what method will a positively charged rod produce a negative charge on a conducting sphere that is placed on an insulating surface?
Charge by induction
Charge by conduction
Charge by convection
None of these
Charge by induction
Charge by induction happens when a charged object is brought in the vicinity of a neutral object. The presents of the charged object will cause the free charges in the neutral object to shift such that the neutral object becomes polarized. When the charged object is positive, this will induce a negative charge on a neutral object.
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