Chapter 11: Dual Nature of Radiation and Matter

the genius April 08, 2026

 

Dual Nature of Radiation and Matter: Class 12 Physics Chapter 11 Notes in Hindi

Ab tak humne padha ki light ek wave hai. Lekin is chapter mein hum dekhenge ki light kabhi-kabhi ek Particle (kan) ki tarah bhi behave karti hai. Isi "Dugni fitrat" ko Dual Nature kehte hain.

1. Electron Emission (Electron Ut-sarjan)

Kisi metal surface se electrons ko bahar nikalne ke liye energy ki zaroorat hoti hai.

  • Work Function ($\phi_0$): Wo minimum energy jo ek electron ko metal surface se bahar nikalne ke liye chahiye. (Iski unit Electron Volt (eV) hoti hai).

2. Photoelectric Effect (Prakash Vidyut Prabhav)

Jab kisi metal surface par suitable frequency ki light girti hai, toh usme se electrons nikalne lagte hain. Inne Photoelectrons kehte hain aur behte hue current ko Photoelectric Current.

Main Observations:

  • Threshold Frequency ($\nu_0$): Wo minimum frequency jiske niche photoemission nahi hota.

  • Stopping Potential ($V_0$): Wo negative potential jis par photoelectric current zero ho jata hai.

3. Einstein’s Photoelectric Equation

Einstein ne bataya ki light "Photons" (energy ke packets) se bani hai.

$$K_{max} = h\nu - \phi_0$$

Yaani, Photon ki energy do kaam karti hai:

  1. Electron ko bahar nikalne mein (Work function).

  2. Electron ko raftar dene mein (Kinetic Energy).

4. Photons ki Properties

  • Photon ki energy: $E = h\nu = \frac{hc}{\lambda}$

  • Photon ka rest mass Zero hota hai.

  • Photons neutral hote hain (In par electric ya magnetic field ka asar nahi hota).

5. de-Broglie Hypothesis (Matter Waves)

Louis de Broglie ne kaha ki agar light wave hokar particle ki tarah behave kar sakti hai, toh particles (jaise electron) ko bhi wave ki tarah behave karna chahiye.

  • de-Broglie Wavelength:

    $$\lambda = \frac{h}{p} = \frac{h}{mv}$$

    (Yahan $h$ Planck’s constant hai aur $p$ momentum).

6. Davisson-Germer Experiment

Is experiment ne prove kiya ki electrons mein wave nature hota hai. Isme electrons ko nickel crystal par strike karwaya gaya aur diffraction pattern dekha gaya.

7. Top Important Questions (Chapter 11)

Short Questions (1-2 Marks):

  1. 1 Electron Volt (eV) kya hai? $1.6 \times 10^{-19}$ Joules ke barabar energy.

  2. Stopping potential intensity par kaise depend karta hai? intensity badhne se stopping potential nahi badalta (ye frequency par depend karta hai).

  3. Threshold wavelength kya hai? Wo maximum wavelength jiske upar photoemission nahi hoga.

Long & Conceptual Questions (3-5 Marks):

  1. Einstein ki photoelectric equation likhiye aur iske 3 main features samjhaiye.

  2. Derive the de-Broglie wavelength for an electron accelerated through a potential $V$:

    $$\lambda = \frac{12.27}{\sqrt{V}} \text{ \AA}$$

  3. Photoelectric effect ke experimental study ka graph banaiye (Current vs Potential).

  4. Explain the failure of wave theory in explaining photoelectric effect.

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