MP Board Class 12 (MPBSE) Dual Nature of Matter — practice questions

Explore 3 free Dual Nature of Matter questions in MP Board Class 12 (MPBSE) Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Dual Nature of Matter questions and exercises with answers

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In a photoelectric experiment, the minimum negative potential applied to the collector plate at which the photocurrent just drops to zero is called theRead the answer and worked solution →The momentum carried by a photon of wavelength $\lambda$ isRead the answer and worked solution →Knock out the photoelectric mythsRead the answer and worked solution →

Worked practice questions

In a photoelectric experiment, the minimum negative potential applied to the collector plate at which the photocurrent just drops to zero is called the

saturation potential
threshold potential
stopping potential
ionisation potential

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Correct answer: C. stopping potential

1. syllabus defines the relevant potentials. The collector plate $A$ is gradually made more negative with respect to the emitter $C$. 2. As the retarding voltage grows, slower photoelectrons cannot reach $A$, so the photocurrent falls. 3. The minimum retarding potential $V_0$ at which even the MOST energetic photoelectrons are just turned back, and the current becomes zero, is the STOPPING potential. 4. Option A (saturation) is the OPPOSITE limit, the positive potential at which all emitted electrons are collected. Threshold (B) refers to a frequency, not a potential. Ionisation potential (D) is an atomic-physics quantity unrelated to surface photoemission. _Source: syllabus Physics Part 2, Ch 11 "Dual Nature of Radiation and Matter", §11.4.2, p. 4 ¶3._

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The momentum carried by a photon of wavelength $\lambda$ is

$h\lambda$
$\dfrac{h}{\lambda}$
$\dfrac{\lambda}{h}$
$h\lambda c$

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Correct answer: B. $\dfrac{h}{\lambda}$

1. A photon has energy $E = h\nu$ and, since it is massless, $E = pc$ where $c$ is the speed of light. 2. Equate: $pc = h\nu$, so $p = \dfrac{h\nu}{c}$. 3. Using $c = \nu\lambda$ gives $p = \dfrac{h\nu}{\nu\lambda} = \dfrac{h}{\lambda}$. 4. The same expression $p = h/\lambda$ is also what de Broglie applied to MATTER. Option A has wrong dimensions ($h\,\lambda$ would have units of action·length). Option C is the reciprocal. **Option D has an extra factor of $c\lambda$.** _Source: syllabus Physics Part 2, Ch 11, §11.7 "Particle Nature of Light: The Photon" + §11.8 (de Broglie hypothesis), pp. 9–11._

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Knock out the photoelectric myths

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Questions

Question
Three of these claims about photoelectric emission are false.
Choices
1. Explanation
  Extra photons add to the count, never to the energy of one electron.
  Item
  Brighter light raises electron energy.
2. Item
  A brighter beam ejects more electrons.
  Correct
  Yes
3. Explanation
  Below the threshold no photon carries enough energy, however many arrive.
  Item
  Bright light works below the threshold.
4. Explanation
  Ejection is instant, well under a billionth of a second.
  Item
  Emission needs a long build up first.
Question
Three of these descriptions of the stopping potential are false.
Choices
1. Explanation
  That is saturation, the opposite end of the same graph.
  Item
  The voltage that collects every electron.
2. Explanation
  Threshold names a frequency, not a potential.
  Item
  The frequency below which none escape.
3. Item
  Retarding voltage that zeroes the current.
  Correct
  Yes
4. Explanation
  Ionisation is an atomic quantity, not surface emission.
  Item
  The energy that frees a bound electron.

Instructions

Tap away the three false claims in each set about photoelectric emission.

_Source: syllabus Physics Part 2, Ch 11 "Dual Nature of Radiation and Matter", §11.4.2, p. 4 ¶3._

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