PHYS 1407 – Conceptual Physics II

Basic Properties of Magnetic Materials and the Magnetic Field

 

Leader: _________________________          Recorder: __________________________

Skeptic: _________________________         Encourager: ________________________

 

Materials


Part 1

Balls, Set w/ Holes

Compass

Electroscope, Leaf

Magnet, Bar

Plastic Coated Wand

2 x Magnet, Ring

Paper Clip, large steel

 

Part 2

Bar magnet

2 x Cow Magnet

Horseshoe magnet

Compass

Sheet of paper

Small amount of iron filings

3d field viewer on instructor’s desk


 

Introduction

In this lab we will qualitatively study some of the basic properties of magnetic materials.

 

Part 1 – Properties of Magnetic Materials

Procedure

Two types of poles

Q1)  Take two of the ring magnets. Bring the two painted sides together. What do you observe?

 

 

Q2)  Bring the two unpainted sides together.  What do you observe?

 

 

 

Q3)  Bring a painted side towards an unpainted side.  What do you observe?

 

 

 

Q4)  Bring a magnet near the electroscope.  Do you see anything?  Can we conclude that the force between magnets is not electric?  Why?

 

 

Q5)  How are the properties of permanent magnets similar to the properties of charges?

 

 

 

Any magnet has two sides with opposite properties which we refer to as a magnetic pole.  It is customary to call one pole the ‘north’ pole and one pole the ‘south’ pole.

 

Q6)  If the painted sides of the magnet have one type of pole and the unpainted side of the magnets have the opposite pole, then what can you conclude about the magnetic force between like and opposite poles?

 

 

Q7)  Bring one end of the compass near the painted side of a magnet.  How does it behave?  (Note bring it close enough to observe an effect but not too close.)

 

 

Q8)  Bring the opposite side of the compass near the painted side of the magnet.  How does it behave? (Note bring it close enough to observe an effect but not too close.)

 

 

 

A magnet like a ring magnet which has two opposite permanent poles is referred to as a permanent magnet. 

 

Q9)  Explain how the observations in Q7) and Q8) demonstrate that the compass is a permanent magnet.

 

 

Identify North and determine which side of the compass needle points north.  We define the pole of the compass that faces north to be the ‘North’ pole of the magnet and the pole that faces south to be the ‘South’ pole of the compass. 

 

Q10)  Given your observations about the behavior of the magnetic forces between like and opposite poles, what type of pole is the painted side of the ring magnet and what type of pole is the unpainted side of the ring magnet?

 

 

Q11)  What type of magnetic pole must Earth’s north pole be?

 

 

Temporary magnets

Q12)  Bring the paper clip near the painted side of the magnet.  What do you observe?

 

 

Q13)  Flip the paper clip over and bring it near the painted side of the magnet.  What do you observe?

 

Q14)  Bring the metal paper clip near the blank side of the magnet.  What do you observe?

 

 

Q15)  Flip the paper clip over and bring it near the blank side of the magnet.  What do you observe?

 

 

Q16)  Does the paper clip always seem to be attracted to the magnet?

 

Materials which are always attracted to a permanent magnet are known as temporary magnets.

 

 

Non magnetic materials

Q17)  Bring the painted side of the magnet near the brass ball.  Do you observe any thing?

 

 

Q18)  Bring the unpainted side near the brass ball.  Do you observe anything?

 

 

Q19)  Based on these observations, does the brass ball appear to be either a permanent or a temporary magnet?  Explain.

 

 

Materials that do not exhibit magnetic properties are known as non-magnetic materials.

 

Classification of magnetic materials

 

Q20)  In the space below, describe a procedure so that you can classify the plastic coated wand, the steel ball, and the aluminum ball as permanent magnets, temporary magnets, or non-magnets. 

 

 

 

Q21)  Carry out your procedure and record your observations.

 

 

Q22)  Classify each of the three objects as a permanent magnet, temporary magnet, or non-magnet.

 

Part 2  The magnetic Field

Magnets affect the space around them just like a charged object does.  The effect of the magnet on space is called the magnetic field and we can see what the magnetic field looks like for different magnets with a very simple procedure.  First we will examine how a magnetic field affects a permanent magnet like a compass needle.

 

Bring the compass needle near the north pole of the bar magnet as shown.

Q23)  On the figure, sketch the orientation of the compass needle.

 

 

 

Now move slowly move the compass needle along the path from near the north pole to near the south pole as shown.  Observe the orientation of the compass needle as you do this.

Q24)  How does the direction the compass needle points change as you move the compass along the path?

 

 

Note that compass needle don’t always point north.  If there is a nearby strong magnet, the magnet will much more strongly influence the compass than the direction of Earth’s magnetic field.

 

Since all dipole magnets have north and south poles, they will all behave similar to the compass needle.  The magnetic field is defined so the direction it points will repel a north pole and attract a south pole.

Q25)  A compass needle originally sits in a magnetic field as shown in the figure above.  Once the compass needle shown in the figure, reaches equilibrium, what direction will it point?

 

 

 

Q26)  Circle one. Compass needles align parallel/perpendicular to the magnetic field.

 

 

All magnetic dipoles will align with a magnetic field and so any magnetic dipole can be used to show the direction of the magnetic field.  A very inexpensive magnetic dipole is the induced dipole in a small filing of iron.

 

Place a sheet of paper over the bar magnet.  Very lightly sprinkle iron filings over the magnet, near the poles, and to the side of the magnet.

 

Q27)  Sketch the appearance of the magnetic field as shown by the iron filings.

 

 

 

Q28)  Do the filling form a pattern over the bar magnet itself?  Describe it?

 

 

Q29)  When the filings line up in straight lines, that indicates a region where the magnetic field is constant.  Does the magnetic field seem to be constant inside the bar magnet?  Explain.

 

 

Carefully pour the filings back into the container and then place the sheet of paper over the cow magnet.  Sprinkle the filings over the cow magnet in a similar fashion.

 

Q30)  Are the patterns similar for the cow magnet and the bar magnet?

 

 

The cow magnet is a much stronger magnet than the bar magnet, but is basically a magnetic dipole.

The magnetic field isn’t just in a plane.  It exists in 3-D.

 

Q31)  Closely examine the iron filings showing the magnetic field for the cow magnet.  Do you see any indication that the field is 3-D?  Explain.

 

 

On the instructor’s desk is a demonstration which shows the magnetic field of a bar magnet in 3-D.  View it.

 

Q32)  Sketch the appearance of the magnetic field for a dipole magnet in 3-D?

 

 

 

Pour the filings back into the container.  Place the sheet of paper over the horseshoe magnet.  A horseshoe magnet is a dipole magnet which is bent so that the N and S poles are near to each other.  Carefully sprinkle the filings over the paper near the horseshoe magnet.

 

Q33)  Sketch the appearance of the field.

 

 

Q34)  Does the field seem to be approximately constant in the region between the poles of the horseshoe magnet?  Explain.

 

 

 

Pour the filings back into the container. 

 

In general, holding a north pole near an equally strong south pole will produce a region with a roughly constant magnetic field.  Try it with two cow magnets.

 

Identify opposite poles for the two cow magnets.  Hold the opposite poles on the table about an inch apart.  Try to get your hands as flat on the table as possible.  Place the sheet of paper over the magnet and sprinkle the iron filings on top.

 

Q35)  Sketch the appearance of the magnetic field.

 

 

Q36)  Did you produce a roughly uniform field between the two opposite poles?  Explain.