Thermionic Emission

• How are cathode rays created?

  By using a strong electric field to pull electrons
• What role does heating the cathode play in thermionic emission?

  It gives electrons enough energy to escape
• What are cathode ray tubes designed to do?

  Fire electrons emitted from the cathode
• What happens to electrons in a cathode ray tube?

  They are accelerated towards the anode
• What is the purpose of the hole in the anode of a cathode ray tube?

  To allow electrons to pass through towards the target
• What is the process of thermionic emission in detail?

  • Heating the cathode (filament)
  • Electrons gain kinetic energy
  • Electrons escape the cathode surface
  • Electrons move towards the anode

  
• What is the formula for work done on an electron in a cathode ray tube?

  W = qV
• How is the speed of electrons in a cathode ray tube calculated?

  Using work done equals kinetic energy
• What is the equation relating work done on an electron and its kinetic energy?

  eV = $\frac{1}{2}mv^2$
• If an electron is accelerated through a potential difference of 500 V, what is the formula to find its speed?

  v = $\sqrt{\frac{2eV}{m}}$
• What is the mass of an electron?

  $9.11 \times 10^{-31} \text{ kg}$
• What is the charge of an electron?

  $1.60 \times 10^{-19} \text{ C}$
• What is the speed of an electron accelerated through 500 V?

  $1.33 \times 10^7 \text{ m/s}$
• What are the steps to calculate the speed of an electron in a cathode ray tube?

  1. List known quantities (mass, charge, potential)
  2. Use the equation: eV = $\frac{1}{2}mv^2$
  3. Rearrange to find velocity: $v =$$\sqrt{\frac{2eV}{m}}$
  4. Substitute known values to calculate speed
• What is the significance of the work done equals kinetic energy concept in experiments?

  It relates energy transfer to electron speed