THE ELECTROMAGNETIC RADIATION G-8

THE ELECTROMAGNETIC RADIATION G-8

RADIATION

is defined as the emission of energy through space in the form of waves.

JAMES CLERK MAXWELL

proposed that visible light consists of electromagnetic waves.

ELECTROMAGNETIC WAVE

• has electric and magnetic field components (according to James Clerk Maxwell)

• produced by the motion of electrically charged particles that travel through empty space, air, or other substances.

ELECTROMAGNETIC RADIATION

• is the emission of energy in the form of electromagnetic waves.

PROPERTIES OF ELECTROMAGNETIC WAVES

• wavelength λ (lowercase Greek letter lambda) is the distance between two successive crests or troughs.

• The amplitude A is the height of a crest or depth of a trough from the middle axis.

• The speed of light c, approximately equal to 3.0 x 10^8 m/s, is the speed of all electromagnetic waves in a vacuum.

• The frequency of radiation f is the number of waves that pass through a given point per unit time.

Frequency f can be calculated as:

f= c/λ

The SI unit of frequency is hertz (Hz), defined as one cycle per second (1 Hz=1 cycle/s). The megahertz (MHz), which you often hear in the radio, is equal too 1 x 10 ⁶ Hz.

The wavelength of electromagnetic waves is usually given in nanometers (nm), where 1nm=1x10^-9m, or in angstrom (Å) = 1x10^-10m.

Visible light (decreasing order of wavelength)

• ROY G BIV

The electromagnetic spectrum

Radiowaves have the longest wavelengths, while gamma rays have the shortest wavelengths.

Multiple Choice

Arrange the following forms of electromagnetic radiation-xrays, UV rays, microwaves- in terms of increasing wavelength.

• microwaves

  UV rays

  x-rays

• X-rays

  UV rays

  microwaves

• UV rays

  Microwaves

  X-rays

Multiple Choice

Arrange the following forms of electromagnetic radiation-xrays, UV rays, microwaves- in terms of increasing frequency.

• microwaves

  UV rays

  X-rays

• UV rays

  X-rays

  microwave

• x-rays

  UV rays

  microwaves

Multiple Choice

Arrange the following forms of electromagnetic radiation-xrays, UV rays, microwaves- in terms of increasing energy.

• microwave

  UV rays

  X rays

• X rays

  UV rays

  Microwaves

• Microwaves

  X rays

  UV rays

MAX PLANCK

• A German physicist, according to him, electromagnetic radiation consists of particles.

• He proposed the idea of QUANTUM THEORY OF RADIATION.

Classical physics vs Quantum physics

According to classical physics, energy is continuous like a ramp, which means any value for energy is possible. In quantum physics, energy comes in discrete packets called quanta, which means energy increases in a stepwise, quantized manner.

Albert Einstein

• In 1905, he proposed that Planck's quanta were bits of energy that he called photons.

• Einstein applied the photon model to explain the phenomenon called photoelectric effect.

• Photoelectric effect occurs when light of a particular wavelength strikes a metal and electrons are ejected from it, causing current to flow in a photocell, which therefore acts as a light activated switch.

ATOMIC SPECTRA

• When light passes through a prism, the ray is refracted or bent. The spectrum of white light (from the sun) produced by refraction of a rainbow of colors with no blank spots or spaces between them.

• CONTINUOUS SPECTRUM is the wide band containing light of all wavelengths.

The line emission spectra of hydrogen, mercury, and neon

Niels Bohr

a Danish physicist, who first proposed a theory of the atom's electronic structure, particularly that of the hydrogen atom.

Bohr's atomic theory proposed a model of the atom which looks like a solar system.

• In this model, the electrons revolve in fixed orbits around the nucleus, as planets do around the sun.

Postulates of Bohr's atomic theory

• Electrons can exist only in certain circular orbits (also called energy levels or shells).

• The energy of an electron in a given orbit is fixed or quantized.

• An electron can jump from one energy level to another

Duality of Matter

• The duality of matter was proposed by Louis de Broglie in 1924.

• According to him, any object can be dual in nature - a wave and a particle.

• wave property is extremely small while for particle is as small as an electron.

UNCERTAINTY PRINCIPLE

(Werner Heisenberg)

• if electrons in an atom have wave properties, it is impossible to determine simultaneously their exact position and exact momentum.

ORBITAL MODEL OF THE ATOM

• ERWIN SCHRODINGER formulated an equation that served as the main basis of the quantum mechanical model or wave mechanical model of an atom.

• The model is more simply referred to as the orbital model of an atom.