Slide 1 / 63 Slide 2 / 63 Chemistry Optional Review Light and Matter 2015-10-27 www.njctl.org Slide 3 / 63 Slide 4 / 63 Light and Sound Light and Sound Because Einstein was able to prove a relationship In 1905 Einstein derived an equation between matter and energy, we today can understand relating mass and energy. You should more about matter by learning all about energy. be familiar with this equation: We can see this relationship between energy and matter E = mc 2 specifically when we look at some of the unusual properties of the wave nature of energy. This equation has been changed a bit since, but a relationship has now, for the first time in history, been established between matter and energy, and between physics and chemistry. Slide 5 / 63 Slide 6 / 63 The Nature of Light: Wave or Particle? Young's Double Slit Experiment The nature of light has been debated for thousands of years. In 1801, Thomas Young settled the argument (apparently) In the 1600's, Newton argued that light was a stream of with his Double Slit Experiment. Later, when we look at the particles. Huygens countered that it was a wave. results of Young's experiment we will see one of the unusual properties of energy that we were talking about. But first, we Both had good arguments, but neither could prove their case. must understand waves. particle! wave! To study the properties of waves we can look at any type of wave, from the waves in a body of water, to the sound waves produced by speakers. Waves are waves. Click here to see a Veritasium video on Young's original Double Slit Experiment
Slide 7 / 63 Slide 8 / 63 Young's Double Slit Experiment Young's Double Slit Experiment This photo is of light (of one color) striking a distant screen after Young tested to see if light was a wave by seeing if it created an passing through 2 slits. This only makes sense if light is a wave. interference pattern when it went through two slits, like a wave would. measurement slit measurement slit screen screen screen screen x d d light light source source L L Slide 9 / 63 Slide 10 / 63 Diffraction and Interference 1 What principle is responsible for light spreading as it passes through a narrow slit? The double slit experiment relies on two properties of waves: diffraction and interference A diffraction Each slit generates a new wave due to diffraction. Those B polarization waves then either constructively or destructively interfere on a dispersion C far away screen. D interference S 1 S 2 viewing screen Slide 10 (Answer) / 63 Slide 11 / 63 Double-Slit Maxima and Minima 1 What principle is responsible for light spreading as it passes through a narrow slit? Interference occurs because each point on the screen is not the same distance from both slits. Depending on the path length difference, the wave can interfere constructively (bright spot) or A diffraction destructively (dark spot). B polarization Answer C dispersion A D interference [This object is a pull tab]
Slide 12 / 63 Slide 13 / 63 2 What principle is responsible for alternating light and Double-Slit Maxima and Minima dark bands when light passes through two or more narrow slits? The bright lines that appear on A diffraction the screen are called maxima. B polarization C dispersion The dark lines are called D interference minima. Maxima are evenly spaced, and a minima occurs between each pair of maxima. Slide 13 (Answer) / 63 Slide 14 / 63 2 What principle is responsible for alternating light and If Light is a Wave… dark bands when light passes through two or more What exactly is waving? narrow slits? A diffraction In sound waves, we know it's the pressure in the air. B polarization C dispersion In any simple harmonic motion there has to be two forms D interference Answer (or levels) of energy and a means to move between them. D But what does that mean for light? [This object is a pull tab] Slide 15 / 63 Slide 16 / 63 Accelerating Charges create E-M waves Accelerating Charges create E-M waves A great way to start this up is to make a charge (like an electron) accelerate. That creates a changing electric field... which creates a changing magnetic field... Electromagnetic Wave Direction which creates a changing electric field... which creates a changing magnetic field... which creates a changing electric field... which creates a changing magnetic field...
Slide 17 / 63 Slide 18 / 63 James Maxwell Maxwell's Equations Maxwell's Equations In Scotland in the late Gauss's Law 1800's, James Maxwell, combined together the Gauss's Law for Magnetism known equations of electricity and magnetism, Faraday's Law of Induction and added one, to create Maxwell's Equations. Ampere's Law Slide 18 (Answer) / 63 Slide 19 / 63 Speed of Light Maxwell's Equations Maxwell’s equations are 4 mathematical equations that relate the electric field (E) and magnetic field (B) to the charge ( ρ ) and current (J) densities that determine the fields and produce electromagnetic He found they predicted that energy could move between two radiation (light). forms (electric and magnetic) and that disturbance must travel Teacher Notes Maxwell's Equations through space at a speed of 3.0 x 10 8 m/s. Gauss's Law for Electricity : the rate of flow of an electric field out Gauss's Law of any closed surface is proportional to the electric charge enclosed This very much agreed with the known speed of light. within the surface. Gauss's Law for Magnetism : the net magnetic flux outside of any Gauss's Law for Magnetism closed surface is 0. Faraday's Law of Induction : the generated voltage around a closed Faraday's Law of Induction loops is equal to the rate of change of magnetic flux through the area of the loop. Ampere's Law : in a constant electric field, the magnetic field around Ampere's Law a closed loop is proportional to the electric current flowing through the loop. 3.0 x 10 8 m/s is the speed of light in a vacuum. [This object is a teacher notes pull tab] Slide 19 (Answer) / 63 Slide 20 / 63 Creating Electromagnetic Waves Speed of Light In physics we learned that a changing magnetic field produces an electric field. He found they predicted that energy could move between two forms (electric and magnetic) and that disturbance must travel Maxwell showed that a changing electric field produces a through space at a speed of 3.0 x 10 8 m/s. magnetic field as well. Teacher Notes This very much agreed with the known speed of light. The speed at which an EM wave travels Once these changing fields are first started up, they keep through a vacuum is related to the electric creating each other...and travel on their own. constant ε 0 and the magnetic constant μ 0 . These traveling fields are called electromagnetic waves. [This object is a teacher notes pull tab] Electromagnetic Wave Direction 3.0 x 10 8 m/s is the speed of light in a vacuum.
Slide 21 / 63 Slide 21 (Answer) / 63 3 An electric field is produced by a 3 An electric field is produced by a A A constant magnetic field. constant magnetic field. B changing magnetic field. B changing magnetic field. either a constant or a changing either a constant or a changing C C Answer magnetic field. magnetic field. B D gravitation D gravitation [This object is a pull tab] Slide 22 / 63 Slide 22 (Answer) / 63 4 A changing electric field will produce a 4 A changing electric field will produce a A A current. current. B B gravitational field. gravitational field. C magnetic field. C magnetic field. D a gravitational field. D a gravitational field. Answer C [This object is a pull tab] Slide 23 / 63 Slide 24 / 63 The Electromagnetic Spectrum c= c= Light is an Electromagnetic Wave Young showed that light is a wave. Maxwell showed that electromagnetic waves exist and travel at the speed of light. Light was shown to be an electromagnetic wave. The frequency of an electromagnetic wave is related to its wavelength. For electromagnetic waves (including light), in a vacuum: c = λ All electromagnetic radiation c = λ travels at the same velocity: c = speed of light the speed of light ( c ) λ = wavelength (m) = frequency (Hz or s -1 ) c = 3.00 x 10 8 m/s.
Slide 25 / 63 Slide 25 (Answer) / 63 5 All electromagnetic waves travel through a 5 All electromagnetic waves travel through a vacuum at vacuum at A the same speed. A the same speed. B speeds that are proportional to their frequency. B speeds that are proportional to their frequency. Answer A C speeds that are inversely proportional to C speeds that are inversely proportional to their frequency. their frequency. D speeds too slow to measure. D speeds too slow to measure. [This object is a pull tab] Slide 26 / 63 Slide 26 (Answer) / 63 6 In a vacuum, the velocity of all electromagnetic 6 In a vacuum, the velocity of all electromagnetic waves: waves: A is zero. A is zero. B B Answer is 3.0 × 10 8 m/s. is 3.0 × 10 8 m/s. B C C depends on the frequency. depends on the frequency. D depends on their amplitude. D depends on their amplitude. [This object is a pull tab] Slide 27 / 63 Slide 27 (Answer) / 63 7 For a wave, the frequency times the wavelength is the 7 For a wave, the frequency times the wavelength is the wave's _______. wave's _______. A speed. A speed. B amplitude. B amplitude. Answer C C intensity. intensity. A D power. D power. [This object is a pull tab]
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