Properties of Light

Charged Particle Interactions

• Any electrically charged object exerts a force on other charged objects.

• Like charges repel one another.

• Unlike charges attract.

• Protons
• positively charged

• Electrons
• negatively charged

Electrical Force

• Electrical force:
• is a universal force
• (every charged particle affects every other charged particle)
• may be attractive or repulsive force
• is always directed along the line connecting two charges
• depends on the product of the two charges
• depends on the distance between the two charges squared
• (obeys the “inverse square rule”)
• Today, physicists describe electric forces in terms of an electrical field produced by the presence of electrical charge.

Charged Particles and Electric Fields

• An electric field extends outward in all directions from any positively charged particle.

• If a charged particle moves, its electric field changes.
• The resulting disturbance travels through space as a wave.

• Electric field strength proportional to 1/r2 .

Magnetic Fields

• If an electric field changes with time (let’s say the source charge wiggles),
• then a magnetic field is created,
• coupled to the time-variant electric field.
• Magnetic fields influence behavior of magnetized objects.
• Earth’s magnetic field causes compass needles to point N
• bar magnets
• electromagnets

Electromagnetism

• Electric and magnetic fields do not exist as independent entities.
• They are different aspects of a single phenomenon:
• Electromagnetism (EMR)

• Together, they constitute an electromagnetic wave that carries energy and information from one part of the universe to another.