name: yen v l
period: 4
date:
1. review: question: recognize what happens to light when it enters water from air.
2. question: what wave travels fastest in solids?
3. question: name the type of wave that travels fastest in a vacuum(space)
4. question: what kind of wave is light: mechanical or electromagnetic?
5. question: which wave needs a medium to travel? mechanical or electromagnetic?
6. question: if a sound wave is moving through the air into water what will happen to its speed? explain why.
7. think about the last time you looked up at the stars. what did you see? what did you think about? do all-stars look the same? why do you think stars are such a source of fascination for people?

Question

Accepted Answer

### Question 1
# Brief Explanations:
When light enters water from air, it undergoes refraction. Refraction is the bending of light as it passes from one medium (air, with a lower optical density) to another (water, with a higher optical density). The speed of light changes when it moves between media with different optical densities, causing the light ray to bend towards the normal (an imaginary line perpendicular to the surface of the water at the point of entry).
# Answer:
When light enters water from air, it refracts (bends) towards the normal because its speed decreases as it moves from a less optically dense medium (air) to a more optically dense medium (water).

### Question 2
# Brief Explanations:
Among the different types of waves, seismic waves (specifically, primary waves or P - waves, which are a type of mechanical wave) travel fastest in solids. Mechanical waves require a medium to travel, and the particles in a solid are closely packed, allowing P - waves (which are longitudinal waves, compressing and expanding the medium) to transfer energy more quickly compared to other mechanical waves like secondary waves (S - waves) or surface waves, and also faster than waves in liquids or gases.
# Answer:
The wave that travels fastest in solids is a primary (P -) wave (a type of seismic/mechanical wave).

### Question 3
# Brief Explanations:
Electromagnetic waves are the type of waves that travel fastest in a vacuum. Electromagnetic waves, such as light waves (including visible light, radio waves, X - rays, etc.), do not require a medium to propagate. In a vacuum, all electromagnetic waves travel at the speed of light, $c = 3\times10^{8}\space m/s$, and this is the maximum speed at which any wave can travel. Mechanical waves, on the other hand, need a medium (like air, water, or solids) to travel and cannot propagate in a vacuum.
# Answer:
The type of wave that travels fastest in a vacuum is an electromagnetic wave (e.g., light waves, radio waves, etc.).

### Question 4
# Brief Explanations:
Light is an electromagnetic wave. Electromagnetic waves are composed of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation. Unlike mechanical waves, electromagnetic waves do not require a medium to travel (they can travel through a vacuum) and are generated by the acceleration of charged particles. Mechanical waves, such as sound waves, require a medium (like air, water, or solids) to transfer energy.
# Answer:
Light is an electromagnetic wave.

### Question 5
# Brief Explanations:
Mechanical waves need a medium to travel. Mechanical waves transfer energy by causing the particles of the medium to vibrate. Examples of mechanical waves include sound waves (which travel through air, water, or solids), seismic waves (which travel through the Earth), and water waves. Electromagnetic waves, however, do not need a medium and can travel through a vacuum (like light traveling from the Sun to the Earth through the vacuum of space) as they are composed of oscillating electric and magnetic fields.
# Answer:
Mechanical waves need a medium to travel.

### Question 6
# Brief Explanations:
When a sound wave moves from air into water, its speed increases. Sound is a mechanical wave, and the speed of a mechanical wave in a medium depends on the properties of the medium, specifically the elasticity and density of the medium. Water is more dense and more elastic than air. The formula for the speed of sound in a medium is related to the elasticity ($E$) and density ($
ho$) of the medium, $v=\sqrt{\frac{E}{
ho}}$. Although water is denser than air, its elasticity (bulk modulus) is much larger, and the net effect is that the speed of sound in water (approximately $1500\space m/s$) is much greater than the speed of sound in air (approximately $343\space m/s$).
# Answer:
When a sound wave moves from air into water, its speed increases. This is because sound is a mechanical wave, and its speed depends on the medium's elasticity and density. Water is more elastic and, although denser than air, the increase in elasticity dominates, leading to a higher speed of sound in water compared to air.

### Question 7
# Brief Explanations:
- **What did you see?**: When looking at the stars, one typically sees a multitude of points of light, varying in brightness and color (some may appear white, others bluish, yellowish, or reddish). There may also be patterns (constellations) formed by groups of stars.
- **What did you think about?**: One might think about the vastness of the universe, the distance of the stars from Earth, what the stars are made of, how they were formed, and whether there are planets around them.
- **Do all stars look the same?**: No, all stars do not look the same. Stars differ in brightness (magnitude), color (which is related to their temperature - hotter stars are bluer, cooler stars are redder), size (some are much larger than others, like supergiants compared to dwarfs), and stage of their life cycle (some are young, some are old and may be in the process of dying).
- **Why are stars a source of fascination?**: Stars are fascinating because they represent the fundamental building blocks of the universe. They are responsible for creating heavy elements through nuclear fusion, which are essential for life as we know it. Their beauty, the mystery of their formation and evolution, and the fact that they are part of a vast, unknown cosmos that sparks human curiosity about our place in the universe all contribute to their fascination.
# Answer:
- **What did you see?**: A sky full of bright, twinkling points of light (stars) with varying brightness and some apparent color differences, along with recognizable constellation patterns.
- **What did you think about?**: The immensity of the universe, the distance of stars from Earth, the nature and composition of stars, and the possibility of other planetary systems.
- **Do all stars look the same?**: No. Stars differ in brightness, color, size, and stage of their life cycle.
- **Why are stars fascinating?**: Stars are fascinating due to their beauty, the mystery of their formation/evolution, their role in creating elements for life, and the curiosity they inspire about the vast, unknown universe.

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