Summer Research Program for Science Teachers

Olu Omoloju

Bronx High School of Science

August 2004

How do compasses work?

Learning Objectives: Students will be able to:

1.      Draw magnetic field lines for a magnet.

2.      Describe the characteristics of magnetic field lines.

Motivation/DEMO:

Place a “see through” compass on an overhead projector.

Place bar magnet next to the compass and follow the field lines with the compass.

Place a transparency over the magnet and pour iron filings over it to get the general pattern.

The Chinese (121 A.D.) found that a suspended iron rod that had been exposed to a natural magnet (lodestone or magnetite) would align itself in the north-south direction.

Why does this happen?

The Earth is magnetic.

Like poles repel [N + N or S + S] and unlike poles [N + S] attract.

 Ø      How are the lines similar to electric field lines? {they pass out of N and into S}   Ø      How can you tell that the magnetic field is strongest near the poles? {more concentrated there}   Ø      How can you tell that the Earth’s magnetic north is really like the south pole of a bar magnet? {the N-pole of the compass needle points towards it}

 Flux lines never cross   Where will the compass point? Where is the flux density greatest? Where is the field greatest? Why does the Flux density increases inside the soft iron?

Magnetic field lines always form closed loops.

Explain in terms of domain theory:

Ø      How metals get magnetized through induction.

Ø      How permanent magnets are formed.

Ø      How hammering a nail will cause it to become magnetized.

STANDARDS:

This Lesson Plan aligns with following National Science Education Standards:

Standard A: Plan an inquiry–based science program.

Standard B: Guide and facilitate learning.

Standard C: Engage in ongoing assessment of teaching and student learning.

Standard D: Design and manage learning environments that provide students with the time, space, and resources needed for learning science.

Standard E: Develop communities of science learners that reflect the intellectual rigor of scientific inquiry and the attitudes and social values conducive to science learning.

Standard F: Participate in the ongoing planning and development of the school science program.

NYC Performance Standards:

S5 – Scientific Thinking

S7 – Scientific Communication