Written Report.docx

CARREON, Vea Ysabel DELFIN, Fatima Kent S. EDICA, Cherrylane 11th grade – Thales of Miletus

3.2.9. LIGHT AS AN ELECTROMAGNETIC WAVE Review of Electromagnetic Theory Development 

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In 1820, Hans Christian Oersted, a Danish physicist and chemist, observed that when a compass was placed near a current-carrying wire, the needle (a small magnet) changed direction. But when there was no current passing through the wire, the needle did not deflect. Jean Baptiste Biot and Felix Savart formulated the force of the magnetic field near a current-carrying wire. Andre-Marie Ampere, a French Physicist, discovered the existence of a magnetic field existed around a current-carrying wire loop whose direction depended on the direction of the current. Michael Faraday found out that if a loop of wire is moved in a magnetic field, voltage is induced and current is produced in the wire, which was called induced current and the process is called electromagnetic induction. o Law of Electromagnetic Induction – states that the electromotive force (emf) induced in a conductor is directly proportional to the rate of change of magnetic flux linking the circuit. Lenz’s Law – the direction of the induced current is always against the change in the magnetic field that has produced it. James Maxwell, a Scottish physicist, was able to establish a system of equations (Maxwell Equations) that describes how electric and magnetic fields are generated and altered by each other.

3.3 THE PARTICLE NATURE OF LIGHT 3.3.1 THE PHOTON THEORY OF LIGHT AND PHOTOELECRIC EFFECT    

In the 1900s, Einstein resurrected the notion that light consists of particles. Particles of light are concentrated bundles of electromagnetic energy. He used the idea of the German physicist, Max Planck, that atoms do not absorb or emit light continuously, but rather do so in small chunks called quanta (plural: quantum). A quantum or a packet of light is called a photon. E = hf

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Photoelectric Effect is the ejection of electrons from photosensitive metals when light falls upon them. The interaction of the light beam with the metal surface consists of collisions between photons and electrons. During the collision, the photons give all their energy to the electrons and disappear.

3.3.2 WAVE NATURE OF MATTER 

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Louis de Broglie said that all matter have wavelengths equal to the quotient of Planck’s constant, h, and momentum which is expressed as: λ = h/p a.k.a. de Broglie’s Wavelength. a. λ stands for the wavelength of the particle b. h stands for Planck's Constant c. p stands for the momentum of the particle Conventional method does not easily detect particles with large masses and small speeds. They have too small wavelength unlike tiny particles such as protons and electrons having observable wavelengths when moving at high speed. An application example for wave nature of matter is electron microscope which wavelength of its electron beams is a thousand times shorter than the wavelength of visible light. Ex: What is the wavelength in meters of a proton traveling at 255,000,000 m/s (which is 85% of the speed of light)? (Assume the mass of the proton to be 1.673 x 10¯27 kg.) 1.) Calculate the kinetic energy of the proton: KE = (1/2)mv2 x = (1/2) (1.673 x 10¯27 kg) (2.55 x 108 m/s)2

x = 5.43934 x 10¯11 J 2.) Use the de Broglie equation: λ = h/p λ = h/√(2Em) x = 6.626 x 10¯34 J s / √[(2) (5.43934 x 10¯11 J) (1.673 x 10¯27 kg)] x = 1.55 x 10¯15 m This wavelength is comparable to the radius of the nuclei of atoms, which range from 1 x 10¯15m to 10 x 10¯15 m (or 1 to 10 fm).

3.3.3 THE ATOMIC SPECTRA 

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Niels Bohr said that the isolated atoms can absorb and emit packets of electromagnetic radiation with discrete energies depending in the atomic structure of the atom. When white light is passed through a spectrograph of prism and light is separated into its color components depending on the wavelength. When atoms are excited they emit light of certain wavelengths which correspond to different colors. The emitted light can be observed as a series of colored lines with dark spaces in between; this series of colored lines is called a line or atomic spectra. Each element produces a unique set of spectral lines. Since no two elements emit the same spectral lines, elements can be identified by their line spectrum.