physics Flashcards
require the presence of a medium
em waves
Can propagate through empty space
electromagnetic waves
are generated by oscillating electric charges
electromagnetic waves
carry energy and momentum
electromagnetic waves
Cover many frequencies
electromagnetic wave
Developed the electromagnetic theory of light
james clerk maxwell
his successful interpretation of the electromagnetic field resulted in the field equations that bear his name
james clerkmaxell
Developed and explained
Kinetic theory of gases
nature of saturn’s ring
color vission
James clerk maxwell
First to generate and detect electromagnetic waves in laboratory settings
heinrich rudolf hertz
the most important discoveries were in 1887
heinrich rudolf hertz
We will assume that the vectors for the electric and magnetic fields in an electromagnetic wave have a specific space time behaviour that is consistent with maxwell’s equations.
Plane electromagnetic waves
assume an electromagnetic wave that travels in the x direction with as shown. the x direction is the direction of the propagation.
plane electro magnetic waves
the electric field is assumed to be in the y direction and the magnetic field in the z direction
plane electromagnetic waves
waves in which the electric and magnetic fields are restricted to being parallel to pair of perpendicular axes are said to be linearly polarized waves
Plane electromagnetic waves
We also assume that at any point in space, The magnitude E and B of the fields depend upon x and t only
plane electromagnetic waves
The collection of waves is called a plane wave.
rays
is a line along which the wave travels
rays
A surface connecting points of equal phase on all waves, called the wave front, is a geometric plane.
Rays
surface connecting points of radiation sends waves out radially in all directions.
Rays
A surface connecting points of equal phase for this situation is a sphere.
rays
Electromagnetic waves transport momentum as well as energy
Momentum
As this momentum is absorbed by some surface, pressure is exerted on the surface
Momentum
Assuming the wave transports a total energy TER to the surface in a time interval Δt, the total momentum is p = TER / c for complete absorption.
Momentum
Various types of electromagnetic waves make up the em spectrum. There is no sharp division between one kind of em wave and the next. All forms of the various types of radiation are produced by the same phenomenon – accelerating charges.
spectrum of em waves
Radio Waves? its length and uses
Wavelengths of more than 104 m to about 0.1 m
Used in radio and television communication system
Microwaves? wavelengths and its uses?
Wavelengths from about 0.3m to m
well suited for radar systems
Microwave ovens are an application
Infared waves? wavelengths and its uses
Wavelengths of about 10-3 m to 7x10- 7 m
Incorrectly called heat waves
produced by hot objects and molecules
readily absorbed by most materials
vissible light?
part of the spectrum detected by human eye
Most sensitive at about 5.5 x 10 -7 m
More about vissible light?
Different wavelengths correspond to different colors
The range is from red ( V ~ 7x 10-7 m ) to violet ( V~ 4x 10-7 m)
Ultraviolet light?
covers about 4x 10-7 m to 6 x m
sun is an important source of uv light
most uv light from the sun is absorbed in the stratosphere by ozone
Xrays?
wavelengeths of about 10-8 m to m
Most common source is the acceleration of high energy electrons striking a metal targe used as a diagnostic tool in medicine.
Gammarays?
Wavelengths of about m to m
emitted by radioactive nuclei
highly penetrating and cause serious damage when absorbed by living tissue
Crab nebula
xray radio waves vissible light infared
production of em waves by an antena
EITHER STATIONARY CHARGES OR STEADY CURRENTS can produce electromagnetic waves
The fundamental mechanism responsible for this radiation is the acceleration of a charged particles
Hertz experiments
An induction coil is connected to a transmitter
the transmitter consist of two spherical electrodes seperated by a narrow gap
the coil provides a short voltage surgens to the electronics
as the air in the gap is ionized its becomes a better conductor
sparks are include to across the gap of the reseing electrodes where the frequency of the receiver was adjusted to match of the transmitter
in a series of other experiments hertz also showed that the radiation generated by this equipment exhibited were properties
interference, diffraction reflection refraction and polarization
he also measured the speed of the radiation
it was close the know value of the speed of the light
