Lecture 1Quantum theory and Photoelectric effect Prepared by: Harminder Singh The basic definition of a wave is the displacement of energy propagating along a medium Edited by: Dr Mukesh . This displacement is the key factor in causing a wave. it releases energy and displaces the particles of the medium.org/C005705/English/Waves/types. causing the water to propagate until another object alters its path. As the water wave is propagating.• If a boat is traveling through water. it pushes the water out of its resting place.thinkquest. http://library.htm Edited by: Dr Mukesh . ‘ Edited by: Dr Mukesh . Wavelength (lambda) is the distance between identical points on successive waves. The frequency (nu) is the number of waves that pass through a particular point in one second. Edited by: Dr Mukesh . Amplitude is the vertical distance from the midline of a wave to the peak or trough. Edited by: Dr Mukesh . • The dull red glow of an electric heater • bright white light of a tungsten light bulb are examples of radiation from heated solids. Prepared by: Harminder Singh . Edited by: Dr Mukesh . Edited by: Dr Mukesh . the color of a hotter object is closer to the blue end of the spectrum and the color of a cooler object is closer to the red. continuous spectrum.Black Body Radiation A black body is an idealized object that absorbs all electromagnetic radiation falling on it. Because no light (visible electromagnetic radiation) is reflected or transmitted. Blackbodies absorb and incandescently re-emit radiation in a characteristic. the higher the frequency. the object appears black when it is cold. and the higher frequency is related to the higher temperature. Thus. Edited by: Dr Mukesh . the shorter the wavelength. This thermal radiation from a black body is termed black-body radiation. However. a black body emits a temperature-dependent spectrum of light. In the blackbody spectrum. It seemed that something fundamental was missing from the laws of classical physics.• Attempts to account for this dependence in terms of established wave theory and thermodynamic laws were only partially successful. • Another theory accounted for the longer wavelengths but failed for short wavelengths. Prepared by: Harminder Singh . • One theory explained short-wavelength dependence but failed to account for the longer wavelengths. Edited by: Dr Mukesh . Edited by: Dr Mukesh . Photoelectric Effect Edited by: Dr Mukesh . e’s out faster = more current. •Light on longer. heats up. Edited by: Dr Mukesh .If we consider light as wave: So if light is classical wave. only intensity. heat more. •Color light does not matter. predict that just puts energy into plate. get diode current voltage curve. Also takes time to heat up. Prepared by: Harminder Singh . Rewriting Equation as Prepared by: Harminder Singh .• Einstein suggested that a beam of light is really a stream of particles. These particles of light are now called photons. • where KE is the kinetic energy of the ejected electron and BE is the binding energy of the electron in the metal.