AST101H1 Chapter Notes - Chapter 5: Diffraction Grating, Incandescent Light Bulb, Electric Charge
5.1 Light in Everyday Life
Radiative energy: the energy that light carries (one of three basic categories of energy)
More concerned with rate at which light transfers energy rather than the total amount of energy it carries
- Rate of energy flow called power, measured in units called watts
- 1 watt = energy flow of 1 joule
Spectrum: a rainbow of light
- White is seen when all colors are mixed in roughly equal proportions (white light)
- Black is what we perceive when there is no light and hence no color
- TV emits only red, green, blue light: primary colors of vision → colors directly detected by cells
in the eyes
- Diffraction grating: a piece of plastic or glass etched with many closely spaced lines to produce
a spectrum
- E.g. bottom of a DVD
Light can interact with matter in four basic ways
1. Emission: a light bulb emits visible light, energy of light comes from electrical potential energy
supplied by light bulb
2. Absorption: when you place your hand near an incandescent light bulb, your hand absorbs some
of the light, whose absorbed energy warms your hand
3. Transmission: some forms of matter (e.g. glass or air) transmit light, allowing it to pass through
4. Reflection/scattering: light can bounce off matter, leading to what is called reflection when the
bouncing is all in the same general direction; scattering when the bouncing is more random
- Materials transmitting light = transparent
- Materials absorbing light = opaque
- Red glass transmits red light, but absorbs other colors
- Green lawn reflects (scatters) green light, but absorbs all other colors
5.2 Properties of Light
Newton proved that white light splits to produce a rainbow of color
- A particle is a thing, a wave is a pattern revealed by its interaction with particles
- Three basic properties of waves
- Wavelength: the distance from one peak (or trough) to the next
- Frequency: number of peaks passing by any point each second (aka cycles per second,
or hertz (Hz))
- Speed: how fast the peaks travel, tells us how fast the energy travels from one place to
another
- Wavelength x frequency = speed
Field: describe the strength of force that a particle would experience at any point in space
- earth creates a gravitational field that describes the strength of gravity at any distance from earth
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Document Summary
Radiative energy: the energy that light carries (one of three basic categories of energy) More concerned with rate at which light transfers energy rather than the total amount of energy it carries. Rate of energy flow called power, measured in units called watts. 1 watt = energy flow of 1 joule. White is seen when all colors are mixed in roughly equal proportions (white light) Black is what we perceive when there is no light and hence no color. Tv emits only red, green, blue light: primary colors of vision colors directly detected by cells in the eyes. Diffraction grating: a piece of plastic or glass etched with many closely spaced lines to produce a spectrum. Red glass transmits red light, but absorbs other colors. Green lawn reflects (scatters) green light, but absorbs all other colors. Newton proved that white light splits to produce a rainbow of color.
