Of the following scientists, who did not contribute to the development of quantum mechanics? (A) Niels Bohr (B) Max Planck (C) Albert Einstein (D) James Clerk Maxwell (E) John Nicholson

Niels Bohr, a Danish physicist, made significant contributions to our understanding of atomic structure and quantum theory. His pioneering work commenced with the proposal of the Bohr model of the atom in 1913.

Bohr suggested that electrons orbit the nucleus in distinct energy levels, or shells, and that these electrons could move between levels by absorbing or emitting a quantum of energy, correlating to a photon. This energy is defined by the formula: \( E = h u \), where \( u \) is the frequency of the emitted or absorbed radiation and \( h \) is Planck's constant.

Bohr's theory explained why atoms emit light at specific wavelengths, forming the basis for quantum mechanics. His concepts, such as quantization of energy and wave-particle duality, were pivotal, as they addressed flaws in classical physics and led to a better understanding of atomic and subatomic processes.

Bohr's Atomic Model

Bohr's model introduced quantized orbits for the electrons, radically changing the way scientists thought about atomic energy levels and the behavior of electrons within atoms. His quantum leap concept was fundamental in explaining how electrons can jump between fixed orbits without existing in between, which was essential for the development of quantum mechanics.

Bohr's perspective was a cornerstone in the field and continues to inform modern scientific inquiry in quantum physics, despite its limitations and the emergence of more complex theories like quantum field theory.

Planck's constant, denoted by \( h \), is a fundamental constant in quantum mechanics, systematically introduced in 1900 by German physicist Max Planck. This constant is paramount to the quantization of energy, which is a key principle of quantum theory.

The value of Planck's constant is approximately \( 6.62607015 \times 10^{-34} \) joule seconds. Planck proposed that energy is not continuous, but rather comes in discrete units or 'quanta'. The formula \( E = h u \) connects the energy \( E \) of a quantum of electromagnetic radiation to its frequency \( u \) using Planck's constant. This was a revolutionary concept that challenged the classical view of energy as a continuous variable.

Significance in Quantum Theory

Planck's constant has proven to be a cornerstone in various quantum phenomena, including the Heisenberg uncertainty principle, which indicates a fundamental limit to what can be known about a particle's position and momentum concurrently. This constant is involved in virtually all quantum mechanical equations, signifying its foundational role in quantum theory and its significant impact on the study of physics at the microscopic level.

The photoelectric effect is an essential phenomenon in quantum mechanics that Albert Einstein described in 1905. Einstein's explanation of the photoelectric effect significantly supported the quantum hypothesis first suggested by Planck.

When light shines on certain materials, it can eject electrons from the surface. This effect cannot be explained by classical wave theories of light, as these theories predict that light's energy is proportional to its intensity, not its frequency. However, experiments show that no electrons are ejected below a certain frequency of light, regardless of the light's intensity.

Einstein used Planck's hypothesis of quantization and proposed that light consists of packets of energy, called photons, with energy given by \( E = h u \). He suggested that if a photon has enough energy (i.e., the light's frequency is high enough), it can give an electron enough energy to escape the material’s surface.

Impact on Quantum Mechanics

The photoelectric effect provided concrete evidence for the particle nature of light and was influential in the development of the dual nature of light as both a wave and a particle. It led to profound understanding in fields such as quantum field theory and the development of various modern technologies, including photovoltaic cells and photo detectors, which are integral in solar power generation and digital cameras, respectively.