PH 202

Quiz # 04 (10 pts)

Name

Solution

 

A charge of  is traveling with a velocity of  enters an unknown magnetic field.  The charge experiences a magnetic force of .  What is the magnitude and direction of the unknown magnetic field?

 

A.

C.

 

 

 

 

B.

D.

 

We know we have to resolve the cross product to determine the direction, so we need  to be the result of a vector crossed with  since that is the result, so from the right hand rule  would give up if we had  but we have a minus sign from the charge we need to deal with so reverse  and make it .  Then we have  which is what we need.  Therefore, we know B points in the East!  Now we can do the math to get the value of B

 

 

 

So Correct Answer is D !

 

An object has a mass  and a charge  and is traveling with a speed  in a direction, which makes a  angle with a magnetic field of strength .  This results in the mass traveling in a circle, which has a radius .  How much work does the magnetic field do if the mass makes 3.0 revolutions around the circle?

 

A.

B.

C.

 

D.

 

 

Since the force created by the magnetic field is a centripetal one and points towards the center of the circle along a radius, and the speed will be tangent to the circle, the force is perpendicular to the displacement of the mass and no work is done by the magnetic field!

 

So Correct Answer is A !

 

An object has a charge .  It is traveling with a velocity .  It encounters a magnetic field described by .  What is the resulting magnetic force acting on the object?

 

A.

C.

 

 

 

 

B.

D.

 

 

Since velocity  is in the  direction and the magnetic field  is in the the result of the cross product is  

 

 

So Correct Answer is C !

 

An ion has lost two electrons so it is charged to +2e.  It has a mass .  It is making a circle of radius  in a magnetic field strength , which is directed into the plane the ion is making the horizontal circles in as shown below.  What is the speed with which the ion is moving around the circle and is it going clockwise or counter clockwise in its orbit?

 

A.

C.

 

 

 

 

B.

D.

 

The Magnetic Force is the Centripetal Force so

 

Solving for

 

 

 

For a positive charge, the force will be directed towards the center of the circle if on the right side of the circle we have the velocity going up then when crossed into B field going into the paper, we get a force going towards the center.  Therefore, if v is going up on the right side, we must be going counter-clock-wise!  So answer is

 

 

So the Correct Answer is A !

 

The source that creates a magnetic field in space is best described by?

 

A.

Stationary Electrical Charges

C.

Moving Electrical Charges

 

 

 

 

B.

Strong Force Interactions (Gluons)

D.

Bosonic Condensation

 

So Correct answer is C !

 

 

 

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This page last updated on September 25, 2020