WAVE-PARTICLE DUALITY
A2 Physics
UNIT 4/PRO
DISCOVERY SHEET
TASK 1:
Evidence of wavelike nature:
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Evidence of
particle-like
nature:
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ELECTRON
Can be diffracted
Produces interference
Has a wavelength
Changes wavelength with
speed!
Point-like (no size???)
Has mass
Produces momentum &
force
Fundamental particle
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LIGHT
Can be diffracted, refracted,
etc
Produces interference
Has a wavelength
No mass
Produces momentum & force
(implies mass!?!?!)
Energy is ‘quantized’
Made of packets called
‘photons’
TASK 2:
Question 1: What does the ‘Photoelectric Effect’ say about the nature of light?

Light carries fixed amounts (QUANTA) of energy and travels in packets
called PHOTONS. Atoms can absorb or emit photons of specific energies.
Question 2: What did de Broglie postulate about the wave nature of particles? Write out
his equation and label the letters in it.
 Particles can be diffracted and produce interference patterns so they must
have a ‘wavelength’:  = h/p. If momentum (p) increases (ie, elecron travels
faster) then  will ger even smaller!
Question 3: Estimate you momentum as you walk out of the door. Use de Broglie’s
equation to estimate your wavelength and comment on why you aren’t diffracted. What
assumptions are we making?
Assume: v = 1m/s, m = 50kg,
Hence:  = h/p = 6.63 x 10-34 / 50
then p = mv = 50 kgm/s.
So,  = 3.315 x 10-35m.
 To be diffracted, the door would have to be around the same size!!!
 We are assuming that we act as a point-like particle.
Question 4: What is Heisenberg’s Uncertainty Principle?
The more accurately we know/measure the position of a particle, the less accurately
we know/measure its momentum (speed). When we multiple the 2 we must have the
same number every time, which is a measure of the intrinsic uncertainty of a system.
TASK 3:
Question 5: Does the speed of an electron affect its wavelength? Explain.
Yes! If it travels faster, it has more momentum. This will decrease its wavelength.
Question 6: How does the electron wavelength affect the diffraction pattern?
If it is faster, it has a smaller wavelength. This will make a diffraction pattern more
spread out (larger rings) and easier to see.
Question 7: How could material scientists make use of the diffraction of electrons?
The faster the electrons travel, the smaller they effectively become when they act as
waves. This allows them to probe smaller structures (eg, inside a nucleus???).