At the time that J. J. Thomson conducted his experiments on cathode rays, the nature of the electron was in doubt. Some considered it to be a form of radiation, like light; others believed the electron to be a particle. Some of the observations made on cathode rays were used to advance one view or the other. Explain how each of the following properties of cathode rays supports either the wave or the particle model of the electron. (a) They pass through metal foils. (b) They travel at speeds slower than that of light. (c) If an object is placed in their path, they cast a shadow. (d) Their path is deflected when they are passed between electrically charged plates.

Long before the definitive proof of electrons' existence, scientists grappled with the true nature of cathode rays. Generated in vacuum tubes, these rays became the subject of intense study. Some researchers suggested they were forms of radiation, while others postulated a particle origin.

The argument for a wave-like nature came from cathode rays' ability to pass through metal foils—a behavior that could suggest diffraction, a wave phenomenon. Yet, the particle theory also held weight, as this could be explained by electrons zipping through the gaps between metal atoms. This dual possibility foreshadowed a profound characteristic of electrons known as 'wave-particle duality.'

Another interesting observation was the speed of these rays, which, unlike light, moved slower, indicating they possessed mass—thus tilting the scale towards the particle theory. Moreover, the formation of sharp shadows when objects blocked these rays suggested they traveled in straight lines, like particles. On the other hand, a wave would typically bend around obstacles in a process known as diffraction.

However, it was the behavior of cathode rays in electric fields that offered a valuable clue. Their path, changing when passing through charged plates, demonstrated an interaction with electromagnetic forces that only charged particles would exhibit. Such findings advanced our understanding of electrons as particles with properties influenced by electric fields.

Wave-particle duality remains one of the most compelling truths in quantum mechanics. The electron, fundamental to chemistry and physics, exhibits this bizarre duality. It behaves both as a particle and a wave, two seemingly mutually exclusive natures.

J.J. Thomson's revolutionary experiments with cathode rays illustrated this perplexing characteristic. The ability of cathode rays to form precise shadows, like particles, contended with their wave-like passage through metal. This paradox was later reconciled by quantum theory, which describes light and matter as having both particle-like and wave-like properties depending on how they are observed.

The principle of duality finds a direct analogy in the real-world scenario where if you observe rolling waves hitting a beach, they seem continuous and fluid. However, when those same waves crash, they spray droplets—a particle-like behavior. In similar respect, electrons can be pinpointed in space showing a particle aspect, yet they also generate interference patterns in experiments like the famous double-slit, showcasing their wave properties.

This duality is essential, not mere scientific curiosity, as it underpins the behavior of all quantum particles, influencing fields ranging from electronics to quantum computing, engaging our attention with the enduring mystery of the quantum world.

Electric fields are omnipresent yet invisible forces that permeate space around charged objects. This concept, indispensable in understanding how charged particles like electrons interact with their environment, becomes particularly evident in the presence of cathode rays.

When cathode rays experience a deflection while passing between electrically charged plates, it's the electric field at work. The field exerts a force on the moving electrons in the rays, altering their straight-line motion and causing them to curve. This illustrates the electric field's influence on particles carrying a charge—providing a direct observation of interaction with unseen forces.

The behavior of cathode rays in electric fields contributed to the electron's understanding as a charged particle. An electric field's strength determines the degree of deflection—an aspect crucial for devices from old CRT televisions to modern particle accelerators. The straightforward movement and predictable response to electric fields make electrons renowned actors in a universe governed by electromagnetism, governing kinetic theories and electrical technologies while also posing interesting questions in the conceptual realm of physicists.