Physics 26 Questions

A changing *electric* field. "If lights were to slow down, its changing electric field would generate a weaker magnetic field, which, in turn, would generate a weaker electric field, and so on, until the wave died out."

A changing *magnetic* field. "If light were to speed up, the changing electric field would generate a stronger magnetic field, which in turn would generate a stronger electric field, etc."

An oscillating or accelerating electric charge. "The vibrating electric and magnetic fields regenerate each other to make up an *electromagnetic wave* which emanates from the vibrating charge."

If light slowed down, its energy would decrease, thereby violating the law of conservation of energy. "There is only one speed for which electric and magnetic fields remain in perfect balance... carrying energy forward without loss or gain." "Energy would be lost and none would be transported form one place to another. So light cannot travel slower than it does."

If light speeded up, its energy would increase, thereby violating the law of conservation of energy. "The changing electric field would generate a stronger magnetic field; a crescendo of ever-increasing field strength and energy," a violation! In a vacuum, all electromagnetic waves move at the same speed and differ from one another in their frequency.

Energy. "Electric and magnetic fiends remain in perfect balance, reinforcing each other as they carry energy through space." pg.488

Radio waves have a lower frequency and longer wavelength than visible light waves. Light waves have a lower frequency and longer wavelength than X-rays. On spectrum, Radio Waves << visible light << X-rays

Less than 1 millionth of 1%, a tiny fraction of the spectrum! Lowest frequency of light visible to us is red, with highest of violet. *roygbiv

Lowest frequency of light visible to us is red, with highest of violet. *roygbiv

They are the same. "The frequency of a wave is the same as the frequency of the vibrating source that creates the wave." "The frequency of an electromagnetic wave as it vibrates through space is identical to the frequency of the oscillating electric charge that generates it."

The wavelength is inversely proportional to the frequency. "waves of low frequency have long wavelengths, and waves of high frequencies have short wavelengths."

300,000 km 300,000 km/s X 1Hz(oscillation per second) = 300,000 km pg. 490

The vacuum of space is full of electromagnetic wave energy. "Montages of electromagnetic waves permeate every part of our surroundings; some are visible are light. Radio waves, free electrons, radiation is everywhere."

The light emitted by resonant vibrations of an electron around one atom can be absorbed by an electron with the same resonant frequency of vibration in another atom. "Vibrations in the emitter are transmitted to vibrations in the receiver."

UV "UV shines on glass, resonance occurs and electrons vibrate to large amplitudes. Energy received by glass atoms is either reemitted or passed onto neighbor atoms by collision. Glass is not transparent to UV light."

Ultraviolet light will be absorbed by the resonant vibration of electrons and turned into internal energy and a temperature increase. "Resonating atoms in glass hold onto UV light energy for a long time, and give up energy as heat."

Visible light will be transmitted by the glass, losing little energy in the process, so the energy remains visible light energy. "Glass is transparent to all frequencies of visible light, passing on reemitted light of same frequency as the incident light."

Infrared light will make atoms vibrate, thus becoming internal energy and a temperature increase. "Frequencies lower than those of visible light cause entire atoms or molecules to vibrate, increasing internal energy and temp." *heat waves

They are the same. "The frequency of the reemitted light is identical to the frequency of the incident light. However, slight time delay lowers average speed of light through a transparent material."

The average speed of light in glass is about 67% of the speed of light in a vacuum. Speed of light in a vacuum is constant 300,000 km/s. (*c*) In glass, speed is 0.67*c* In water, speed is 0.75*c* In diamond, speed is 0.41*c*

They are the same. The incident light is at speed *c* Through the glass, speed is 0.67*c* The emergent light is at speed *c* again.

Infrared light vibrates entire atoms and molecules, and this vibration increases the temperature of the absorbing substance.

Vibrations given by the light to their electrons, atoms, and molecules that absorb the light become internal energy, thus leading to a temperature increase. "They absorb light without reemitting it. Vibrations turn into random kinetic energy."

Free electrons in metals vibrate when light strikes them, thereby reemitting the light as reflected light.

Light bounces around inside the transparent water region covering a wet object, getting absorbed more on each bounce. Incident light on dry surfaces bounce directly to your eye.

No light from the source enters the shadow in an umbra, while some, but not all, light from the source enters the penumbra.

Yes, they both cast shadows. When one passes into the shadow of the other, there is an eclipse. Solar: Earth passes in Moon's shadow Lunar: Moon passes in Earth's shadow

The rods are rod-shaped and are more sensitive to dim light; cluster in periphery. The cones are cone-shaped and are color-sensitive; cluster near fovea

When they are moving. "The periphery is very sensitive to motion. We are wired to look for movement to the side of our visual field."

our emotions! dilate with pleasure, contract with aversion.

Since the shadow of the relatively small moon on the large Earth covers a very small part of Earth's surface, only relatively few people are in the shadow of the moon during a solar eclipse. But the shadow of Earth that covers the moon during a lunar eclipse is in view of everybody who can see the moon in the nighttime sky. Sun>>moon>>Earth = small shadow (Solar) Sun>>Earth>>moon = large shadow (Lunar)

The frequency of reemitted light is identical to the frequency of incidental light. At this speed, energy is carried forward withouth loss or gain. There is a time delay between absorption and reemission. It is this time delay that results in a lower average speed of light through a transparent material.

...vibrating electric charges, which emit vibrating electric and magnetic fields

The clouds allow UV light to pass through, but glass does not allow UV light to pass through. Glass only lets in visible light.

A high flying airplane is farther away from a surface (ground), thus the shadow is less distinct or nonevident as the penumbra expands into a big blur. A low flying airplane casts a sharp shadow since it is near the ground surface, with light coming from slightly different directions not spreading out much below it. (a larger umbra)

You are seeing the delay for the light to reach your eye.