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CBSE NOTES CLASS 12 PHYSICS

CHAPTER 11 DUAL NATURE OF RADIATION AND MATTER

Causes of cathode ray emmission

Properties of cathode rays

Photon

Photoelectric effect

Work function

Threshold frequency

Threshold wavelength

Laws of photoelectric effect

Effect of intensity of incident light on photoelectric current

Effect of potential on photoelectric current

Effect of frequency on photoelectric current

Photoelectric emission is an instantaneous process

Failure of wave theory in explaining photoelectric effect

Einstein’s photoelectric equation: energy quantum of radiation

Particle nature of light

Wave nature of matter

Heisenberg’s uncertainty principle

CBSE NOTES CLASS 12 PHYSICS

CHAPTER 11 DUAL NATURE OF RADIATION AND MATTER

Properties of cathode rays

  1. Cathode rays are not electromagnetic rays.

  2. Cathode rays are deflected by electric field and magnetic field.

  3. Cathode rays produce heat when they fall on the metals.

  4. Cathode rays can pass through thin aluminium or gold foils without puncturing them.

  5. Cathode rays can produce physical and chemical change.

  6. Cathode ray travel in straight line with high velocity, momentum and energy and cast shadow of objects placed in their path.

  7. On striking the target of high atomic weight and high melting point, they produce X-rays.

  8. Cathode rays produce fluorescence and phosphorescence in certain substance and hence affect photographic plate.

  9. When any charged particle move in a field where magnetic and electric fields are present, without any deviation, then Magnetic force = Electrostatic force

    Bev = Ee or v =EB


  10. Specific charge of cathode rays means the ratio of charge and mass. Specific charge of electron

    em=E22VB2

    where,

    E = electric field,

    B = magnetic field and

    V = potential difference applied across ends of tube.

    em =  1.7589 × 1011 C/kg.

    Charge on electron e = -1.602 × 10-19 C.

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