for de Broglie waves
for de Broglie waves
for de Broglie waves
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Ex 3.3 :<br />
An e' has a <strong>de</strong> <strong>Broglie</strong> wavelength of 2pm=2x10 -12 m.Find its<br />
kinetic energy & the phase & group velocity of its <strong>de</strong> <strong>Broglie</strong><br />
<strong>waves</strong>.<br />
2 2 2<br />
(a) E =E o +kE kE =E – E o = Eo<br />
p c Eo<br />
pc = hc/λ= (4.136x10 -15 ev.s)(3x10 8 m/s)/(2x10 -12 ) =<br />
6.2x10 5 ev=620kv<br />
the rest energy of e' is E o =511kv<br />
2<br />
2<br />
kE= 511 620 511 292 kev<br />
(b) e' velocity<br />
2<br />
Eo<br />
E <br />
E<br />
v c 1<br />
o<br />
2 0. 771c<br />
2<br />
1<br />
v<br />
E<br />
2<br />
c<br />
∴ v p = c 2 /v =1.3c , v g = v = 0.771c<br />
10
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