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PHYSICS, M7 2019 VCE 16 MC

Students are conducting a photoelectric effect experiment. They shine light of known frequency onto a metal and measure the maximum kinetic energy of the emitted photoelectron.

The students increase the intensity of the incident light.

The effect of this increase would most likely be

  1. lower maximum kinetic energy of the emitted photoelectrons.
  2. higher maximum kinetic energy of the emitted photoelectrons.
  3. fewer emitted photoelectrons but of higher maximum kinetic energy.
  4. more emitted photoelectrons but of the same maximum kinetic energy.
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\(D\)

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  • The energy of a photon (which is transferred to the photoelectron) is independent of the intensity of the light.
  • Increasing the intensity of light will not change the maximum kinetic energy of the photoelectrons.
  • However, a higher intensity of light corresponds to more photons and thus more emitted photoelectrons.

\(\Rightarrow D\)

PHYSICS, M7 2023 HSC 23b

The James Webb Space Telescope (JWST) is sensitive to wavelengths from  6.0 \(\times\) 10\(^{-7}\) m  to  2.8 \(\times\) 10\(^{-5}\) m.

What is the minimum photon energy that it can detect?  (3 marks)

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\(E_{\text{min}}= 7.1 \times 10^{-21}\) \( \text{J}\)

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  • The minimum photon energy corresponds to the minimum frequency.
  • Minimum frequency occurs at the maximum wavelength as frequency and wavelength are inversely proportional.
\(E_{\text{min}}\) \(=hf\)  
  \(=\dfrac{hc}{ \lambda}\)  
  \(=\dfrac{6.626 \times 10^{-34} \times 3 \times 10^8}{2.8 \times 10^{-5}} \)  
  \(=7.1 \times 10^{-21}\) \(\text J\)  

PHYSICS, M7 2023 HSC 15 MC

What evidence resulting from investigations into the photoelectric effect is consistent with the model of light subsequently proposed by Einstein?

  1. Photoelectrons were only ejected from a metal if the light was less than a specific wavelength.
  2. Increasing the intensity of light on a metal increased the maximum kinetic energy of the photoelectrons.
  3. If photons had sufficient energy to eject photoelectrons from a metal, the maximum kinetic energy was independent of the type of metal used.
  4. The probability of photoelectrons being emitted from a metal was proportional to the duration of exposure to light for any given wavelength used.
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\(A\)

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  • A photoelectron will be ejected from a metal if the energy of the photoelectron transferred from the photon is greater than the work function of the metal surface where
  •    \(K_{\text{max}}=hf-\phi\ \ \Rightarrow \ \ K_{\text{max}}=\dfrac{hc}{\lambda}-\phi\)
  • By decreasing the wavelength of the light, the maximum kinetic energy of the photoelectron increases, thus it has enough energy to overcome the work function of the metal and be ejected from the surface of the metal.
  • Increasing the intensity of the light increases the number of photons but has no effect on the maximum kinetic energy of the photoelectrons.

\(\Rightarrow A\)

♦ Mean mark 46%.