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Dual Nature of Radiation and Matter — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsDual Nature of Radiation and Matter4 Marks
Question
When light of sufficiently high frequency is incident on a metallic surface, electrons are emitted from the metallic surface. TI1is phenomenon is called photoelectric emission. Kinetic energy of the emitted photoelectrons depends on the wavelength of incident tight and is independent of the intensity of light. Number of emitted photoelectrons depends on intensity. $(\text{h}\upsilon-\phi)$ is the maximum kinetic energy of emitted photoelectrons (where $\phi$ is the work function of metallic surface). Reverse effect of photo emission produces X-ray. X-ray is not deflected by electric and magnetic fields. Wavelength of a continuous X-ray depends on potential difference across the tube. Wavelength of characteristic X-ray depends on the atomic number.
  1. Einstein's photoelectric equation is:
  1. $\text{E}_\text{max}=\text{h}\upsilon-\phi$
  2. $\text{E}=\text{mc}^2$
  3. $\text{E}^2=\text{p}^2\text{c}^2+\text{m}_0^2\text{c}^4$
  4. $\text{E}=\frac{1}{2}\text{mv}^2$
  1. Light of wavelength $\lambda$ which is less than threshold wavelength is incident on a photosensitive material. If incident wavelength is decreased so that emitted photoelectrons are moving with some velocity then stopping potential will:
  1. Increase.
  2. Decrease.
  3. Be zero.
  4. Become exactly half.
  1. When ultraviolet rays incident on metal plate then photoelectric effect does not occur, it occur by incident of:
  1. Infrared rays
  2. X-rays
  3. Radio wave
  4. Micro wave
  1. If frequency $(\upsilon>\upsilon_0)$ of incident light becomes n times the initial frequency $(\upsilon)$, then K.E. of the emitted photoelectrons becomes ($\upsilon_0$ threshold frequency).
  1. N times of the initial kinetic energy.
  2. More than n times of the initial kinetic energy.
  3. Less than n times of the initial kinetic energy.
  4. Kinetic energy of the emitted photoelectrons remains unchanged.
  1. A monochromatic light is used in a photoelectric experiment. The stopping potential.
  1. Is related to the mean wavelength.
  2. Is related to the shortest wavelength.
  3. Is not related to the minimum kinetic energy of emitted photoelectrons.
  4. Intensity of incident tight.
✓

Answer

  1. (a) $\text{E}_\text{max}=\text{h}\upsilon-\phi$
  1. (a) Increase.
Explanation:
According to Einstein's photoelectric equation,
$\text{eV}_0=\frac{\text{hc}}{\lambda}-\frac{\text{hc}}{\lambda_0}$
As $\lambda_0$ is constant, so when $\lambda$ is decreased, stopping potential $(V_0)$ increases.
  1. (b) X-rays
Explanation:
It indicates that threshold frequency is greater than that of ultraviolet light. As X-rays have greater frequency than ultraviolet rays, so they can cause photoelectric effect.
  1. (b) More than n times of the initial kinetic energy.
Explanation:
$\text{K.E.}_1=\text{h}\upsilon-\phi$
$\text{K.E.}_2=\text{nh}\upsilon-\phi=\text{n}(\text{h}\upsilon-\phi)+(\text{n}-1)\phi$
$\text{K.E.}_2=\text{nKE}_1+(\text{n}-1)\phi$
$\text{K.E.}_2>\text{nKE}_1$
  1. (b) Is related to the shortest wavelength.
Explanation:
Stopping potential is the measurement of maximum kinetic energy of emitted photoelectrons and kinetic energy of emitted photoelectrons is linearly related with the frequency of incident light corresponding (i.e., corresponding to shortest wavelength, K.E. is maximum).
Stopping potential is independent of intensity.

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