Discovery of an Electron and Electron Diffraction Flashcards
(32 cards)
What is thermionic emission?
The release of electrons from a heated cathode due to the energy supplied by heat, similar to the photoelectric effect but with thermal energy.
What is meant by βspecific chargeβ of an electron?
Specific charge is the charge-to-mass ratio of a particle:
π/π.
What equation relates kinetic energy to accelerating potential?
πππ = 1/2 ππ£Β², where ππ is the accelerating potential.
How is speed of an accelerated electron calculated?
π£ = β(2πππ/π).
Method 1 - Parallel plates with electric & magnetic fields: Whatβs the principle?
Balance electric and magnetic forces:
πΈπ = π΅ππ£ β π£ = πΈ/π΅.
Method 2 - Magnetic field only (circular path): Key formula?
π΅ππ£ = ππ£Β²/π β π/π = π£/(π΅π).
Method 3 - Parabolic motion in electric field (no magnetic field): Why less common?
Requires electron speed, which depends on π/π, making the method somewhat redundant.
What did Millikanβs experiment measure?
The charge of a single electron.
What forces act on an oil droplet at terminal velocity?
Gravitational force ππ = drag force 6ππππ£.
How was radius of the droplet found?
Using π = (9ππ£Β²)/(2ππ).
How did Millikan calculate charge on a droplet?
When levitated in an electric field:
πΈπ = ππ β π = (ππ)/(ππ).
What fundamental value did Millikan deduce?
π = 1.6 Γ 10β»ΒΉβΉ C, the elementary charge.
What does electron diffraction demonstrate?
Electrons act like waves, showing interference patternsβevidence of wave-particle duality.
What is the de Broglie wavelength formula?
π = β/(ππ£), where β is Planckβs constant.
Why do larger particles not diffract noticeably?
Their mass is too large, making π too small to observe.
How do we adjust electron speed to observe diffraction?
Electrons must be fast enough to pass through foil but not too fastβhigher speed β smaller π.
Why do electrons accelerate toward the anode?
Because of the electric field created by a potential difference between the negatively charged cathode and the positively charged anode.
What form of energy do electrons gain during acceleration?
Kinetic energy: πΈπ = 1/2 ππ£Β².
How is potential difference related to energy and charge?
π = πΈπ β πΈ = ππ.
How do you calculate electron speed from an electron gun?
π£ = β(2πππ/π), where ππ is the accelerating voltage.
How is electric field strength between plates calculated?
πΈ = π/π, where π is the separation between plates.
What force acts on an electron in an electric field?
πΉ = ππΈ.
What direction is force on a moving charge in a magnetic field?
Perpendicular to both the velocity and the magnetic field (Flemingβs Left Hand Rule).
What provides centripetal force in electron circular motion in a magnetic field?
Magnetic force: πΉ = π΅ππ£ = ππ£Β²/π.
