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AQA A Level Physics > Wave-Particle Duality > Flashcards

Wave-Particle Duality Flashcards

1
Q

What was Newton’s Corpuscular Theory of Light

A

Light was made of small particle-like bodies called corpuscles, emitted by luminous objects

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2
Q

What was one of the predictions of Newton’s Corpuscular Theory of Light

A

Objects emitting light were losing mass slowly

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3
Q

What phenomena could Newton’s Corpuscular Theory of Light explain

A

Reflection, refraction and dispersion but NOT diffraction

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4
Q

How did Newton’s Corpuscular Theory of Light explain reflection

A

The corpuscles hit the reflective surface and experienced an equal and opposite repulsive force from the surface due to N3L

This is because corpuscular theory treated corspuscles like solid, elastic spheres

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5
Q

How did Newton’s Corpuscular Theory of Light explain refraction

A

At a boundary between air and denser medium, there was a resultant force on the corpuscles acting perpendicular to the boundary.

This meant light travelled faster in a more dense medium

Corpuscles were attracted to the denser medium

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6
Q

Where does the boundary force arise in Newtons explanation of refraction

A

There is an attraction to a greater amount of matter, increasing the vertical component of velocity

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7
Q

What did Huygen propose about light

A

Light was a wave

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8
Q

Huygen’s theory of light

A

Light travelled in wavefront.
The wavefront were emitted from a point source
Any point of the wavefront acted as a secondary point source from which wavelets could propagate.
Wavelets joined together to form new wavefront.

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9
Q

How did Huygens theory of light explain reflection

A

When wavefront hits a reflective surface, point of reflection becomes secondary point source for wavelets.

Different parts of wavefronts hit reflective surface at different times, so new wavefront formed in new direction

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10
Q

How did Huygens theory of light explain refraction

A

Relied on light travelling slower in denser mediums.
Different parts of wavefront hit boundary at different times.
Part of wavefront which reaches boundary first slows down first and causes it to change direction

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11
Q

Similarities between Newtons and Huygens theories of light

A

Both explained :
reflection
refraction
dispersion

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12
Q

Differences between Newtons and Huygens theories of light

A

Corpuscular theory said light travelled faster in denser mediums, wave theory said light travelled slower in denser mediums.

Corpuscular theory said light was composed of particles with mass, wave theory said it was a wave travelling through a massless medium.

Corpuscular theory had no explanation for diffraction or interference

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13
Q

Why was Newtons theory more accepted than Huygens

A

Newton was more widely known and respected.
There was also no way of measuring speed of light or observing diffraction at the time.

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14
Q

What does Young’s double slit experiment demonstrate

A

How light waves produce a diffraction pattern

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15
Q

Describe the set up for Young’s double slit experiment

A

Monochromatic light source
Single slit
Double slit
Screen

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16
Q

What pattern did Young’s double slit experiment show

A

A interference pattern

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17
Q

What did corpuscular theory predict for Young’s double slit experiment

A

Only 2 bright regions

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18
Q

What was evidence of Huygens wave theory of light

A

Light diffracts through slits to form an interference pattern

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19
Q

What are electromagnetic waves

A

Oscillating electric and magnetic fields which propagated each other

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20
Q

Direction of electric field on an accelerating charge

A

Perpendicular to the particles motion

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21
Q

What does the alternating electric field of a charged particles produce

A

A perpendicular alternating magnetic field

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22
Q

Does light need a medium to travel

A

No

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23
Q

State Maxwell’s formula for the speed of EM waves in a vacuum and explain why speed of light is constant.

A

c = 1 / √(μ₀ε₀)
All values are constants therefore speed of EM waves in a vacuum is constant

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24
Q

What does μ₀ relate to

A

Magnetic flux density due to a current carrying wire in free space

25
What does ε₀ relate to
The electric field strength due to a charged object in free space
26
What did Hertz discover
Radiowaves
27
How did Hertz discover radiowaves
He made a short air gap between wires and put a large pd across this gap The high pd spark bridged the gap. The sparks generated radiowaves
28
Describe the equipment Hertz used to detect radiowaves
A circular wire with a small break in the circuit which produced spark across the break when near the source. A concave metal sheet with 2 parallel metal rods at the centre with an oscillating potential difference induced across them by the radio waves alternating magnetic field
29
Describe how Hertz measured the speed of radio waves
He reflected radio waves from the transmitter off of a flat metal sheet. This produced a standing wave. When passing a detector, a large signal was detected at antinodes and no signal at the nodes. This allowed him to find the wavelength. Frequency was already known using properties of the transmitter circuit. He used v = f x λ to determine speed
30
How did Fizeau measure the speed of light
He shone a beam of light at a mirror several km away. In the path of the light he placed a toothed wheel which spun at a very high speed. Teeth of wheel and gaps inbetween periodically passed over the beam of light This created regular pulses of light travelling towards distant mirror
31
Derivation for how Fizeau was able to calculate speed of light
total time for light to pass and return through toothed wheel = 2d/c t = T / 2n (wheel has n gaps and n teeth both of same width) t = 1 / 2nf 2d/c = 1/2nf c = 4dnf
32
Perfect black body
A theoretical object that absorbs all of the radiation incident on it and does not reflect or transmit any radiation
33
What wavelengths are emitted when an objects temperature increases
Shorter wavelengths
34
Ultra-violet catastrophe
The disagreement with experimentally measured black body spectra and the spectra predicted by physics
35
What did the spectra when treating EM radiation as a wave predict
It emits an infinite amount of ultra-violet as temperature of object increased
36
What was Planck's interpretation
Oscillators were responsible for emitting EM radiation and he assumed energy emitted was quantised, which meant it could only be emitted in integer multiples of these quanta of energy
37
Describe the photoelectric effect
Incident radiation on a metal's surface causes it to emit electrons. This only happens for radiation above a certain frequency. If radiation is below the threshold frequency, no matter the intensity, no photoelectrons will be emitted
38
How did wave theory contradict the photoelectric effect
It predicted if low frequency radiations was aimed at the metal at a high enough intensity, enough energy would be transferred to remove photoelectrons.
39
What did Einstein propose about EM radiation
It was made from discrete quanta/ packets of energy of size: E =hf
40
How did Einsteins theory explain why radiation below threshold frequency did not cause photoelectric emission
Only one photon was able to transfer its energy to one electron If hf was not large enough to energise an electron, the photons could not combine to energise the electron
41
How did Einsteins theory explain why the energy of emitted photoelectrons increased with the frequency of incident light
Photon transferred all their energy, hf, to electrons If this was greater than energy needed to emit electrons, rest of energy was transferred to the KE store of the electrons. If hf was larger, more energy was left over for KE of electrons.
42
What was DeBroglie's hypothesis
All particles can behave as both waves and particles
43
Derivation to find the wavelength of electrons
eV = 1/2 x mv^2 v = sqrt (2eV / m) momentum = mass x velocity momentum = m x sqrt (2eV / m) momentum = sqrt(m^2) x sqrt (2eV / m) momentum = sqrt (m^2 x 2eV / m) momentum = sqrt (2meV) wavelength = h / sqrt (2meV)
44
What happens to the DeBroglie wavelength of an electron as speed increases
Wavelength decreases
45
What happens to electron interference pattern if pd increases
The diffraction rings move closer to the centre of the screen
46
What does changing the voltage across the anode allow scientists to do
Manipulate the wavelength of the electron
47
What does the resolving power of a microscope depend on
The wavelength of the radiation being used Shorter wavelength = see finer details in an object
48
Size of an atom
1x10^-10m
49
How do scientists find wavelengths the size of an atom
They estimate the anode voltage/accelerating voltage needed to make electrons wavelength the same size as an atom
50
How do electrons travel in a transmission electron microscope (TEM)
Electron gun emits electrons through thermionic emission. The e- are accelerated to high speeds by a large potential difference.
51
Function of condenser lens in TEM
Produces parallel beam of electron waves to illuminate the sample
52
Purpose of objective lens in TEM
Produces an image of the sample
53
Purpose of the projector lens in TEM
Creates magnified image
54
Drawbacks of TEM
Level of detail depends on resolving power (fast electrons and short wavelength) Electrons must pass through sample Not all electrons emitted by thermionic emission have same speed so not all electrons slowed by sample same amt Electrons in beam have range of speeds so blurrier image
55
Explain the process of quantum tunnelling
Waves have a probability of travelling through potential barrier
56
What size gap can electrons tunnel across
A barrier the same order as the DeBroglie wavelength
57
Explain how a STM can map the shape of a sample when the height of the probe is kept constant
Tip moved across sample. Current is measured. When the current is larger, gap is smaller and sample closer to the tip
58
How is a constant current STM different
Height of top is varied so current constant. Height of tip is measured and corresponds to profile of sample

AQA A Level Physics (23 decks)

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