Magnetic Fields
Visualizing magnetic influence with compasses, field direction, and field strength
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B) Magnetic Fields - regions in space where a magnetic forces may be detected
Magnetism
We will focus on fields around:
1) current carrying wire
2) permanent & electromagnets
3) Bar Magnets
A Magnetic Field is Curved A magnetized needle moving near a magnet
Magnetic lines of force of a bar magnet shown by iron
filings on paper:Magnet
from
(Actual magnetic fields contain
NASA
Solar Flames are deflected by the suns magnetic field
1. Magnetic flux lines - lines of magnetism in a magnetic field.
- magnetic field is not continuous.
Between each line of magnetism
... no magnetic field
a) The needles of a compass line up perfectly with the flux lines
3D Magnetic Field of a Bar Magnet
b) The arrows on a flux line show where the North Pole of a compass would point in that field.
Source Unknown
Compass / Bar Magnet
c) Magnetic force strongest at the ...
At Poles ...
... where flux lines are closest.
Cutting Magnets ...
... each piece is a brand new magnet
How can magnets attract non-magnets?
St. Mary's Physics YouTube Channel
Directions: Slide the magnet on the right over to the metal on the left. (unmagnetized metal on left)
Certain metals contain magnetic regions called
domains.
Ex) Which diagram best represents magnetic flux lines around a bar magnet?
Flux lines don't cross, Out of North into South
d) Measuring the strength of a magnetic field
Put a wire with a known current into the field and measure the force on the wire
Where does the north pole
Earth's Magnetic Field
What are these magnetic lines called? Where is the field strongest?
Mina Gong - Class of 2009
Flux lines, The field is strongest at the poles
Established 1995 Use any material on this site (w/ attribution) |
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Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. A magnetic field is best defined as:
2. Outside a bar magnet, in which direction do the arrows on magnetic flux lines point?
3. Where is the magnetic field of a bar magnet strongest?
4. A bar magnet is cut in half. What do you get?
5. How can a magnet attract an unmagnetized piece of iron?
Mapping a Field With Compasses
Students placed small compasses at many points around a bar magnet on a table and recorded the direction each needle pointed. They used the results to draw magnetic field lines.
Which statement correctly describes the field lines outside the bar magnet?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response.
C2. Where is the magnetic field strongest?
C3. The bar magnet lies on the table with its north pole on the right. A magnetic field sensor placed directly above the middle of the magnet (toward the top of the page) reads 2.0 mT. Choose the direction of the magnetic field at that point, and enter its magnitude.
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C4. Place a check mark in three boxes to indicate the statements that correctly describe magnetic field lines.
C5. Can two magnetic field lines ever cross?
C6. The students are given a second bar magnet whose poles are not labeled. Describe how they could use a compass to identify its north pole, and explain why the method works.