How was Becquerel convinced at first that his hypothesis was supported?

Henri Becquerel was initially convinced that his hypothesis was supported when he observed an unexpected phenomenon during his experiments with uranium salts. He hypothesized that the recently discovered X-rays by Wilhelm Roentgen in 1895 were related to the fluorescence properties of certain materials.

To test his hypothesis, Becquerel wrapped photographic plates in black paper to protect them from light exposure and placed uranium salts on top of the paper. He then exposed this setup to sunlight, believing that the sunlight would cause the uranium salts to fluoresce and emit radiation similar to X-rays, which would penetrate the paper and expose the photographic plate.

However, due to overcast weather, he couldn't perform the experiment as planned. He stored the wrapped plates and salts in a drawer. After several days, when he developed the photographic plates, he was surprised to find a clear image of the uranium salts on the plates despite the lack of sunlight. This accidental discovery was a strong indication that the uranium salts were emitting some form of radiation on their own, without the need for an external source of energy like sunlight. Becquerel found that this spontaneous emission of radiation (which we now know as radioactivity) was a property of the uranium atoms themselves, not caused by an external factor like fluorescence.

This unexpected result supported his hypothesis in a way he had not anticipated, showing that the uranium salts were indeed emitting some form of penetrating rays; however, these rays were different from X-rays as they did not require an external energy source like sunlight.

Extra: Henri Becquerel's discovery was a key moment in the field of physics, leading to the understanding of radioactivity. Radioactivity is the process by which unstable atomic nuclei release energy in the form of radiation. This can happen in different forms such as alpha particles (helium nuclei), beta particles (electrons or positrons), and gamma rays (high-energy electromagnetic radiation).

Becquerel's work paved the way for Marie Curie and her husband, Pierre Curie, to further investigate these mysterious rays. The Curies discovered that not only did uranium exhibit this behavior, but also other elements such as thorium and the new elements they discovered, polonium and radium. The work on radioactivity earned Henri Becquerel, Marie Curie, and Pierre Curie the Nobel Prize in Physics in 1903.

Understanding radioactivity has profound implications in various fields including nuclear power generation, medical diagnostics and treatments, and archaeological dating through techniques like carbon-14 dating. The concept of radioactivity also contributed significantly to the development of quantum theory, as it presented a challenge to classical physics, leading scientists to explore new models of the atom and the forces operating within and around it.