Light - wave or particle? Flashcards
What did the photoelectric effect show?
What did Max Planck suggest EM waves are released in?
The photoelectric effect in the 19th century showed light acts as a particle.
Max Planck suggested EM waves can only be released in discrete packets - quanta. A single packet of EM radiation is a quantum.
What is the first formula for energy?
E=hf where h=Planck constant=6.6*10^-34, and f=frequency.
The higher the frequency, the more …. wave packets carry.
What did Einstein suggest EM waves exist in?
The higher the frequency of EM energy, the more energy its wave packets carry. Einstein suggested EM waves exist only in discrete packets, photons, acting like particles.
What features/behaviour did Einstein attribute to photons?
Einstein argued EM wave packets have no charge like neutrons, and transfer all or none of their energy.
What is an electronvolt, and what’s the formula?
Electron volts are easier to measure.
An electron volt is the kinetic energy an electron gains when accelerated through 1V, losing electrical potential energy as it travels between 2 electrodes.
eV=1/2mv2
1eV = 1V* (1.6*10^-19)C
What voltage is needed for current to flow, and what is this same voltage needed for by the electrons? What is KE gained transferred to after acceleration?
Planck’s constant can be found using LEDs.
Current can only pass with a threshold voltage, Vo, the voltage needed to give electrons the same energy as released photons from the LED. All KE after acceleration is transferred to the photon.
