Modern Physics

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1. Conductors

1. Conductors are materials that allow the easy flow of electric current.
2. Their conductivity is due to the presence of free electrons.
3. Examples include metals such as copper, aluminum, and silver.
4. Conductors have very low resistivity (10⁻⁶ to 10⁻⁸ Ω·m).
5. They are widely used in electrical wiring and electronic circuits.

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1. Introduction to Cathode Rays

1. Cathode rays are streams of electrons emitted from the cathode in a vacuum tube.
2. They were first observed by J.J. Thomson, who identified them as negatively charged particles (electrons).
3. Cathode rays are produced when a high voltage is applied across a vacuum tube with a cathode and anode.
4. They travel in straight lines and cause fluorescence when they strike certain materials.

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Types of Radioactive Decay

Radioactive decay is the process by which an unstable nucleus loses energy by emitting radiation. The three main types of radioactive decay are:

Bohr’s Atomic Model

1. Proposed by Niels Bohr in 1913 to address the limitations of Rutherford’s atomic model.
2. Electrons move in specific quantized orbits around the nucleus without radiating energy.
3. These orbits are called energy levels or shells, denoted by n (n = 1, 2, 3...).
4. The energy of an electron is constant in a specific orbit.
5. An electron can move to a higher orbit by absorbing energy or to a lower orbit by emitting energy

1. An atom is the smallest unit of matter that retains the properties of an element.
2. It consists of a nucleus at the center and electrons orbiting around it.
3. The nucleus contains protons (positively charged particles) and neutrons (neutral particles).
4. Electrons are negatively charged and occupy distinct energy levels or shells.
5. Atoms are electrically neutral because the number of protons equals the number of electrons.

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