Download Electromagnetic Waves

Electromagnetic
Waves
Electric Charge
Two types: positive and negative
Like charges repel, opposites attract
Forces come in a matched pair
Each charge pushes or pulls on the other
Forces have equal magnitudes and opposite directions
Forces increase with decreasing separation
Charge is quantized
Charge is an intrinsic property of matter
Electrons are negatively charged (-1.6 x 10-19 coulomb’s each)
Protons are positively charged (+1.6 x 10-19 coulomb’s each)
Net charge is the sum of an object’s charges
Most objects have zero net charge (neutral – equal numbers of + and -)
Electric Fields
Charges push on each other through empty space
Charge one creates an “electric field”
This electric field pushes on charge two
An electric field is a structure in space that pushes on electric charge
The magnitude of the field is proportional to the magnitude of the force on
a test charge
The direction of the field is the direction of the force on a positive test
charge
Magnetic Poles
Two Types: north and south
Like poles repel, opposites attract
Forces come in matched pairs
Forces increase with decreasing separation
Analogous to electric charges EXCEPT:
No isolated magnetic poles have ever been found!
Net pole on an object is always zero!
Most atoms are magnetic, but most materials are not
Atomic magnetism is perfectly cancelled
Material is indifferent to nearby magnetic poles
Some materials do not have full cancellation
Ferromagnetic materials respond to magnetic poles
Magnetic Fields
A magnetic field is a structure in space that pushes on magnetic poles
The magnitude of the field is proportional to the magnitude of the force on
a test pole
The direction of the field is in the direction of the force on a north test pole
Electromagnetism (part 1)
Magnetic fields
Push only on magnetic poles
Are produced by magnetic poles
Can also be produced by changing electricity!
Electric fields
Push only on electric charges
Are produced by electric charges
Can also be produced by changing magnetism
Electromagnetism (part 2)
Magnetism created by
Poles (but isolated poles don’t seem to exist
Moving electric charges
Changing electric fields
Electricity created by
Charges
Moving magnetic poles
Changing magnetic fields
Electromagnetic Waves
Accelerating charge emits electromagnetic waves
Charge produces electric field
Current (moving charge) produces magnetic field
Changing current (accelerating charge) produces changing magnetic
field, which produces changing electric field, which produces
changing magnetic field, which produces changing electric field,
which …
An electromagnetic wave consists only of an electric and magnetic field
An electromagnetic wave travels through empty space at the speed of light
Structure of Electromagnetic Waves
Electric filed is perpendicular to
magnetic field
Electric field creates magnetic
field and vice versa
Electric field determines
polarization of the wave
Electromagnetic Spectrum
Long-wavelength electromagnetic waves: Radio and microwave
Medium-wavelength: infrared, visible, and ultraviolet light
Short-wavelength: X-rays and Gamma-rays