Properties of Matter and Light

Atomic mass represents the average mass of all isotopes of a given element.
It incorporates significant figures (sig figs), indicating the precision of the measurement.
This average mass is a composite of all naturally occurring isotopes for that element.

When individual particles (protons and neutrons) form a nucleus, they become more stable as a group than they are as individual, separate particles.
If this increased stability did not occur, an atom would not naturally form in the first place.

Wavelength ( $\lambda$ ):
- Defined as the distance between two successive peaks (or crests) of a wave.
- For example, in water waves, it's the distance from the top of one wave to the top of the next wave.
Frequency ( $\nu$ ):
- Refers to how often something happens or the number of wave cycles passing a point per unit of time.
- Example: If standing in water, counting $10$ waves hitting your feet in one minute represents the frequency.
Speed of Light ( $c$ ):
- Light travels at an incredibly fast speed.
- Even at this speed, it takes a relatively long time for light to travel from the Sun to the Earth due to the vast distance involved.
Wave Interference:
- When waves interact, they can undergo interference.
- Constructive Interference: Occurs when a crest meets another crest, resulting in a larger wave. In the context of light, this is observed as bright light.
- Destructive Interference: Occurs when a crest meets a trough, resulting in a smaller wave or potentially nullifying the wave. This would manifest as darker light or the absence of light.
- Explaining certain phenomena, like electric current, purely using wave theory can be challenging.

For some phenomena, considering light as particles (photons) provides a more intuitive explanation than wave theory.
Photons: Discrete packets of light energy.
Energy of Photons:
- Photons carry energy, and their interaction can cause effects, similar to how an object (e.g., a water bottle) can be knocked over by a physical impact (analogous to receiving sufficient photon energy).
Vision and Light Regulation (Pupil Function):
- Our eyes adjust to varying light conditions by controlling the amount of light (photons) that enters.
- Pupil Dilation: In darker environments, pupils enlarge (dilate) to allow more photons to enter the eye, enhancing vision.
- Pupil Constriction: In brighter environments, pupils shrink (constrict) to reduce the number of photons entering.
- Overexposure: If a person moves from a dark space to bright sunlight, their pupils may still be dilated, allowing too many photons to enter, which can temporarily overwhelm the sense of vision until the pupils constrict.