The correct option is **C. Wave-Particle Duality**. ### Explanation of the Correct Answer **Wave-Particle Duality** is a fundamental concept in quantum mechanics that describes how light and other forms of electromagnetic radiation exhibit both wave-like and particle-like properties. This duality is essential for understanding various phenomena in physics, such as interference patterns, the photoelectric effect, and the behavior of electrons. 1. **Wave Nature of Light**: Light behaves as a wave when it exhibits phenomena such as interference and diffraction. For example, when light passes through a double slit, it creates an interference pattern on a screen, which is characteristic of waves. This behavior can be described using wave equations, such as the wave equation \( v = f \lambda \), where \( v \) is the speed of light, \( f \) is the frequency, and \( \lambda \) is the wavelength. 2. **Particle Nature of Light**: Light also behaves as a particle, which is evident in the photoelectric effect. In this phenomenon, light shining on a metal surface can eject electrons from that surface. This effect can only be explained if light is considered to be made up of particles called photons, each carrying a discrete amount of energy given by the equation \( E = hf \), where \( E \) is the energy of the photon, \( h \) is Planck's constant, and \( f \) is the frequency of the light. 3. **Quantum Mechanics**: The concept of wave-particle duality is a cornerstone of quantum mechanics, which describes the behavior of particles at the atomic and subatomic levels. It suggests that particles like electrons and photons do not fit neatly into the classical categories of "particle" or "wave" but instead exhibit properties of both depending on the experimental conditions. ### Explanation of Why Other Options Are Incorrect - **A. The Law of Conservation of Energy**: This law states that energy cannot be created or destroyed, only transformed from one form to another. While it is a fundamental principle in physics, it does not specifically address the dual nature of light. It applies broadly to all physical processes, not just those involving light. - **B. The Uncertainty Principle**: Formulated by Werner Heisenberg, this principle states that certain pairs of physical properties, like position and momentum, cannot be simultaneously known to arbitrary precision. While it is a crucial concept in quantum mechanics, it does not directly explain the dual behavior of light as both a wave and a particle. - **D. Newton's First Law of Motion**: This law states that an object at rest stays at rest, and an object in motion stays in motion unless acted upon by a net external force. This principle pertains to classical mechanics and does not relate to the wave-particle duality of light. ### Summary of Key Points - **Wave-Particle Duality** explains that light exhibits both wave-like and particle-like properties. - Light behaves as a wave in phenomena like interference and diffraction. - Light behaves as a particle in phenomena like the photoelectric effect, where it is made up of photons. - This concept is fundamental to quantum mechanics and helps explain the behavior of particles at the atomic level. ### Revision Summary - Light exhibits both wave and particle characteristics, known as wave-particle duality. - Wave behavior is demonstrated through interference and diffraction patterns. - Particle behavior is shown in the photoelectric effect, where photons eject electrons. - Wave-particle duality is a key concept in quantum mechanics, essential for understanding modern physics.