x Despite hypothesising that amplitude intensity of a wave was related to a

X despite hypothesising that amplitude intensity of a

This preview shows page 13 - 14 out of 44 pages.

x Despite hypothesising that amplitude (intensity) of a wave was related to a wave’s eng which should result in increase max E k of electrons, did not explain why Max E k changed with freq of incident light used. x Could not explain work function/ threshold freq Support for the particle model = Flaws in wave model from photoelectric effect experiment Particle diffraction Matter scattering Davisson and Germer bombarded nickel crystals with electrons x Speed of electrons known due to set accelerating voltage x Maximum and minimum intensities were located at different angles recorded by a detector (Similar to young’s double slit ) Electrons had undergone interference (once thought to be an exclusive wave property) Electrons fringe spacing and path difference used to calculate wavelength of electron (0.14nm) this value verified De Broglie’s wavelength formula: using known velocity controlled by the accelerating v & mass of an electron (9.11 x 10 -31 kg) Main relationships for the experiment: [1] E k Voltage [2] E k = mv 2 [3] [4] W (work on electron) = q (charge: 1.6x10 -19 C) x V (volts) = E k Double accelerating voltage: 2 xE k = Increases v by factor of = Decreases wavelength by factor of Absorption/emission spectra Incandescent lights electricity sent through gas vapour to excite electrons Electrons absorb eng releasing thermal eng as photons (Evidence for quantised discrete eng levels ) Support for the dual nature of matter____________________ x Discrete eng levels for particles (electrons) Electrons moved in waves inside their eng levels (quantised) x Standing waves are the eng levels electrons exist within; o nly certain λ of light will promote electrons (resonance) Circumference of electron orbit = = nλ (standing wave ) forming a stable orbit x (n=1,2,3 ...) n = 1 (ground level), n=2 (1 st excitation state), etc. If an integral number of wavelengths cannot fit into the circumference of electron orbit, destructive interference occurs and the orbit (wavelength) is not an eng level Left to right: n =3,4,5,6 Light and Matter Wave Model Particle Model x Light beams cross paths undisturbed x Refraction (Snell’s Law) x Inverse Sq. law (I ) x Linear Propagation x Reflection x Linear Propagation x Reflection x Inverse Sq. law (I ) Could not explain: x Photoelectric Could not explain: x Refraction x Waves transfer of eng without the net transfer of matter x Mechanical waves Requires a medium to propagate through x Wave Amplitude maximum displacement a particle in a mechanical wave has from its origin x Periodic Wave Source of disturbance undergoes continual oscillation producing a constant wave Light Properties Eng, no mass, no charge n = 0 n = 1 n = 1 n = 1 n = 1 n = 2 n = 2 n = 2 Second minima Location of node Swap terminals of battery (+ve terminal faces cathode) for -ve voltage at cathode (location of light) This gives the max E k Monochromatic light used for this experiment -ve terminal towards cathode: Accelerating voltage (voltage not impeding photocurrent) -ve terminal towards cathode: Accelerating voltage (voltage not impeding photocurrent) Stopping voltage How much work done by load to stop
Image of page 13
Image of page 14

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture