WHAT IS ELECTROMAGNETIC WAVE?

Electricity and magnetism are different facets of electromagnetism. This connection first elucidated by Faraday, Maxwell.

 

Faraday’s Law:  A changing magnetic field will create an electric field.  The direction of the electric field will be perpendicular to the direction of the magnetic field.

Maxwell’s Proposal:  A changing electric field will create a magnetic field.  The direction of the magnetic field will be perpendicular to the direction of the electric field.

RELATION BETWEEN ELECTRICITY & MAGNETISM

A changing magnetic field produces an electric field, and a changing electric field produces a magnetic field.

Electric and Magnetic fields can produce forces on charges

An accelerating charge produces electromagnetic waves (radiation)

Both electric and magnetic fields can transport energy

      Electric field energy used in electrical circuits, e.g., released in lightning

      Magnetic field carries energy through transformer

ELECTROMAGNETIC WAVE

The electromagnetic wave is looked at as sinusoidal waves which are composed of a combination of two fields which are i) electric field and ii) a magnetic field at right angle to that electric field.

 

All electromagnetic radiation travels at c =  3x10⁸ m/s in vacuum – real number is 299792458.0 m/s exactly

Examples of Electromagnetic Radiation

•          AM and FM radio waves (including TV signals)

•          Cell phone communication links

•          Microwaves

•          Infrared radiation

•          Light

•          X-rays

•          Gamma rays

 

Uses of Electromagnetic Waves

 

•  Communication systems

•    Radar

•    Cooking (with microwaves)

•    Medical Imaging (X rays)

•    “Night Vision” (infrared)

•     Astronomy (radio, mwave, IR, visible, UV, gamma)

 

WHAT IS LEAK RATE IN VACUUM SCIENCE?

Ideally it is impossible to build a vacuum system with out any leak. Without active pumping the pressure in a real system will rise with time. 

Pressure rise is produced by outgassing and by gas molecules penetrating through leaks from the outside into the vacuum system.

 The leak rate must be small enough not to prevent to reach the required pressure level.

A real leak will yield a linear pressure rate-of rise curve. The slope of the curve is a function of the leak rate and the volume of the system: 

 

Leak is related to how many molecules per unit time are being admitted into volume.

According to the gas laws, if volume, temperature and pressure are specified, it is possible to determine how many molecules are there inside the volume.

Torr-liter defines the molecules contained in a one liter volume at a pressure of 1 Torr at 0 °C.

 22.4 liters of gas at 760 Torr and 0 °C equals 6.02x10²³ molecules (Avogadro’s number)

 1 Torr-liter would then contain about 3.5 x 10¹⁹ molecules.

std cc represents the number of molecules contained in a 1 cc volume at a pressure of 760 Torr and 0°C

1 std. cc contains about 2.7 x 10¹⁹ molecules 

 The leak rate is defined as the pV-throughput of a gas through a leak.

 It is a function of the type of gas, pressure difference and temperature.

 In a system of volume V the leak

Here Δp is the pressure rise during the time interval Δt .