In a 1905 paper that later won him a nobel prize, albert einstein postulated that the energy of light was proportional to its frequency. The constant of proportionality turned out to be planck’s constant h : elight
The Correct Answer and Explanation is:
Albert Einstein’s 1905 paper on the photoelectric effect postulated that the energy of light is directly proportional to its frequency. This groundbreaking idea was a key contribution to the development of quantum theory. Einstein’s theory was based on Max Planck’s earlier work, which had introduced the concept of energy quantization in relation to blackbody radiation. Einstein extended this idea to explain the photoelectric effect, where light shining on a metal surface ejects electrons from that surface.
The key equation that Einstein proposed was:
[
E = h \cdot f
]
Where:
- ( E ) is the energy of a photon (a particle of light),
- ( h ) is Planck’s constant (approximately ( 6.626 \times 10^{-34} \, \text{J·s} )),
- ( f ) is the frequency of the light.
Explanation:
- Energy and Frequency: According to Einstein, light doesn’t just behave as a wave (as was traditionally believed), but also exhibits particle-like properties. These particles, called photons, each carry energy proportional to their frequency. The higher the frequency of light (such as blue or ultraviolet light), the more energy each photon carries. In contrast, lower-frequency light (such as red light) carries less energy per photon.
- Planck’s Constant: The proportionality constant ( h ), known as Planck’s constant, links the frequency of the light to the energy of the photon. This constant is fundamental in quantum mechanics and establishes the quantization of energy. The discovery that energy is quantized was revolutionary because it challenged the classical wave theory of light, which did not account for this discrete energy transfer.
- Photoelectric Effect: Einstein’s postulate provided a clear explanation for the photoelectric effect. In this phenomenon, light of a sufficiently high frequency (above a certain threshold) can eject electrons from a metal surface. The energy of the emitted electrons depends on the frequency of the incident light, not its intensity, as classical wave theory would have predicted. This observation was one of the key pieces of experimental evidence supporting quantum theory.
Einstein’s work on the photoelectric effect earned him the Nobel Prize in Physics in 1921, as it confirmed the quantum nature of light and laid the foundation for modern quantum mechanics.