Physics 4.5

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How does electromagnetic radiation travel through space?

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Quantum physics

22 Terms

1

How does electromagnetic radiation travel through space?

As a continuous wave

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2

What are photons?

Discrete energy packets

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3

When does electromagnetic radiation act as photons?

When it interacts with matters

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4

What is the equation linking energy of a photon to frequency of the electromagnetic radiation?

E = hf = hc / lamda

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5

What is h?

  • Planck constant

  • 6.63×10^-34

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6

What is 1 electronvolt?

The energy transferred when an electron travels through a potential difference of 1 volt

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7

What is 1 electronvolt in joules?

1eV = 1.60×10^-19J

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8

What is the photoelectric effect?

When electromagnetic radiation is shone onto a metal electrons are released from the surface

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9

What happens if you try to use visible light for the photoelectric effect?

No electrons will be removed from the plate

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10

What is the work function of a metal?

Minimum energy required to free an electron from the surface of the metal

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11

What must a photon have in order to free an electron from a metal surface?

Energy at least as great as the work function

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12

What is threshold frequency?

Minimum frequency required of the electromagnetic radiation to free electrons from the surface of the metal

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13

Does visible light produce the photoelectric effect?

No as the frequency is too low

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14

What is the photoelectric equation?

hf = phi + KEmax

  • phi = work function of the metal

  • KEmax = max ke of released electron

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15

What determines the KE of a released electron?

Amount of energy left after it is released (after using up work function amount)

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16

How does intensity of radiation relate to electron emission if frequency < threshold frequency?

no electrons will be released regardless

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17

How does intensity of radiation relate to electron emission if frequency > threshold frequency?

increasing intensity increases rate of electron emission as it increases the number of photons available to interact with the electrons

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18

How can you increase the kinetic energy of the released electrons?

Increase the frequency of radiation further above the threshold so there's more energy left over

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19

What is wave particle duality?

  • diffraction and superposition of light relies on the radiation acting as a wave

  • Photoelectric effect relies on it acting as discrete photons

  • Therefore electromagnetic waves have a dual nature

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20

What is the de broglie equation?

Lamda = h/p = h/mv

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21

What can the de Broglie equation be applied to?

All particles with mass

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22

How can electrons be used as evidence for wave-particle duality?

  • electrons are particles with mass and charge, they can be accelerated and deflected by magnetic and electric fields

  • However they can also be made to diffract when fired at thin polycrystalline graphite which is a property of waves

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