CHEM1811 Lecture Notes - Lecture 7: Wave Packet, Planck Constant, Sodium-Vapor Lamp
CHEM1811
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Lecture 04
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ffi!ffit.' Lecture 4: Light as particles
CHEM1811: Engineering Chemistry 1A
Stuart Prescott
Room 706
Chemical Sciences Building (F10)
Recap: Light as a wave
Waves are continuous
Can vary intensity by varying
amplitude
Any amplitude is possible
Any amount of energy is possible
(a) Trvo complete cycles of
s'aveleagth i
: l,eiiiitfsc:Xatt . I '. :'. : :
Frequency (z), wavelength (.\),
speed (c)
(b) lVavclenslh half of that in (a);
frequency twi@ as greatas
in {a)
ffi
(c) Same frequency as (tr),
smailer amplitude
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Shining light on metal
Discovered by Hertz in 1887,
shining light on metal can make a
current flow:
L/j
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ffi$i
O€uiblrglMt ffiqp"v,
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Document Summary
Frequency (z), wavelength (. \), speed (c) (a) trvo complete cycles of s"aveleagth i. I ". ffi (b) lvavclenslh half of that in (a); frequency twi@ as greatas in {a) (c) same frequency as (tr), smailer amplitude. Discovered by hertz in 1887, shining light on metal can make a current flow: There was a maximum wavelength (minimum frequency) to eject electrons from the metal. Light with u > 4. 60 x 1o1a hz causes caesium to emit electrons. If it is a question of having enough energy, then shine a more intense light for longer! The need for a minimum energy that cannot be satisfied by a more intense light implies that light is a particle not a wave. ffiuxt. y" What if light were a particle as well energy of each photon for a given as a wave? frequency: A p. lrotop, of. light is a; wave packet. Since light is also a wave: c: u\ ( c. {h)
