PH 202

Quiz # 05 (10 pts)

Name

Solution

 

In a village in the far north, the Earth’s magnetic field points straight down and has a field strength .  A power line is  long and carrying a current  and the current is going in the due north direction.  What is the magnitude and direction of the magnetic force acting on the power wire?

 

A.

B.

C.

 

D.

 

 

 

Since  acts down and  is due North, the cross product provides the direction by the right hand rule due West!

 

 

 

So Correct Answer is C !

 

A square coil with  turns of wire has a side length  and a current

  flowing through the coil as indicated in the diagram to the right.  The normal of the plane makes an angle  as shown.  The magnetic field is going to the right as shown and has a field strength

.  What is the magnitude of the magnetic moment µ of this coil and in which direction will the coil rotate due to the magnetic field B that is present?

 

A.

C.

 

 

 

 

B.

D.

 

 

By the right hand rule the direction of the magnetic moment is up and to right along the dotted line shown.  Since the torque acting on the coil is to align  with , the coil will rotate clockwise!

 

So Correct Answer is A !

 

 

Two straight wires each  long are shown above.  One is located at the origin of the x axis and the other is located  to the right on the x axis.  The left one is carrying  going into the plane of the paper, while the right one is carrying  coming out of the plane of the paper as shown in the diagram.  What is the magnitude and direction of the magnetic force the left  wire is exerting on the right wire?

 

A.

C.

 

 

 

 

B.

D.

 

And at the location of the right wire

 

Since the current for the right wire is out of paper, the right hand rule gives the final direction of the force as to the right!

Combining the expressions, we get:

 

 

 

 

 

So Correct Answer is B !

 

A powerful electromagnet is made from a circular coil which is  in radius, has turns of wire and is measured to have a resistance of .  What voltage must be applied to this coil to produce a magnetic field strength of  at the center of the coil?

 

A.

B.

C.

 

D.

 

 

For a circular coil, the magnetic field strength at the center can be found from the relation

 

Solve for the current needed

Now use Ohm’s Law

Solve for V and plug in the needed current i

 

 

 

 

So the Correct Answer is D !

 

An ion has a  net charge, a mass of , and a velocity .  It is supposed to pass through a velocity selector which is composed of both a magnetic field and an electric field which are at right angles  to each other.  The electric field which is shown is

 .  What is the magnitude and direction of the magnetic field that will allow this ion to continue traveling in a straight line with the same speed it has currently?

 

A.

C.

 

 

 

 

B.

D.

 

The direction of  must create a magnetic force that balances the electric force, so the electric force is going to point down .  So the magnetic force must point up or .  To get that we remember

 

Since q is positive and   points in  we need  to point  , therefore we need  to point into paper  for the cross product to give us the right direction for the force!

 

The net force acting on the ion can be written as:

 

 

So

 

So Correct answer is B !

 

 

 

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This page last updated on October 2, 2020