science test 1

Magnetism

• Magnetism is a non-contact force
• Magnetic forces can act between objects not touching

Learning Objectives

• Explain what a magnetic field is
• Explain how magnetic flux lines show the strength of the magnetic force
• Identify the principle allowing magnetic fields to interact
• Draw simple magnetic fields, like that of a bar magnet

Magnetic Field

• Magnetic materials in a magnet's field experience magnetic force
• Earth acts like a giant magnet, attracting particles from space to the north and south poles
• These particles create auroras in Earth's atmosphere

Magnet Field (continued)

• A magnetic field is the area around a magnet where a magnetic force exists
• Magnetic flux lines (magnetic field lines) show the magnetic field around a magnet
• Iron filings align with the field lines, demonstrating the field
• The closer together the flux lines, the stronger the field
• Flux lines exit the north pole and enter the south pole of a magnet

Think, Pair, and Share

• Iron filings pattern shows the magnetic field's shape and strength
• Field lines are closer together near poles, indicating stronger strength there
• Other materials (e.g., pepper, sawdust, nickel, copper) can show magnetic fields

Magnetic Field Lines

• Magnetic flux lines always emerge from the north pole and enter the south pole of a magnet
• Lines curve around to enter the south pole in bar magnets

Strength of a Magnetic Field

• The strength of a magnetic field is shown by how close together the magnetic flux lines are
• Close lines denote a strong field, spread lines imply weak field
• The field is stronger near the poles than the sides of a bar magnet

1-Minute Table Task

• A magnetic field is the area around a magnet where magnetic materials experience a force
• Direction of magnetic field lines indicate the direction of the field at a point
• Iron filings can visualize the field's shape and direction
• The spacing of flux lines denotes magnetic field strength

Quick Quiz

• Magnetic flux lines emerge from the north pole and enter the south pole
• Close flux lines indicate a strong magnetic field

Practical: 1 Magnetic Field

• Draw the shape and label the poles of a bar magnet
• Draw field lines around the magnet
• Label the positions where:
  • Iron is attracted to the south pole
  • Iron is attracted to the north pole
  • Iron experiences equal attraction from both poles
  • Iron experiences little or no field from the magnet

Interactions Between Two Magnets

• When magnets are close, their fields interact
• Similar field directions lead to a stronger combined field (attraction)
• Opposing field directions result in a weaker field (repulsion)

Repulsion of Like Poles

• Opposite field directions cause the fields to cancel, weakening the magnetic force
• Like poles (N-N or S-S) repel

Practical: 2 Magnets Together

• Draw two pairs of magnets (N-S and N-N) a few cm apart
• Draw the magnetic field lines for each pair
• Label areas of strong field
• Label areas where opposing magnetic fields balance

Earth's Magnetic Field

• Earth's magnetic field protects from charged particles from the sun
• Mercury also has a magnetic field, but it's weaker and more vulnerable to solar wind

Earth's Magnetic Field (continued)

• Compasses aligning with north-south direction show Earth has a magnetic field
• North pole of a compass needle points to Earth's magnetic south pole (or very close)
• Magnetic poles periodically reverse

Earth's Magnetic Field: Additional Questions

• Why does Earth have a magnetic field?
• Describe the similarities and differences between magnetism and gravity
• How can evidence be collected whether other planets have magnetic fields?

Discuss with a Seatmate

• Summarize the evidence for Earth's magnetic field

The Geodynamo Theory

• Evidence for Earth's core structure (earthquakes, volcanoes, rocks) suggests a solid iron core surrounded by a liquid iron-nickel outer core
• Earth's rotation creates currents in the liquid core
• These currents produce a magnetic field (geodynamo)

Impact of Earth's Magnetic Field

• Earth's magnetic field compresses on the day side and extends greatly on the night side, deflecting solar winds