Chapter 22
Light & The
Electromagnetic Spectrum
Electromagnetic waves are transverse waves that consist of electricand magneticfields. (see p. 632)
The electric and magnetic fields vibrate at right angles to each other (perpendicular).
When one field vibrates, so does the other.
Electromagnetic radiation is the energy that is transferred by electromagnetic waves.
A mediumis not needed!
All electromagnetic waves travel the same speed.
This is about 300,000,000 m/s!!!
(or 300,000 km/s)
*This is in a vacuum; EM waves may pass through certain media, but slow down as they do.
Light: wave or particle?????
- Light has many properties of waves:
Polarized light has passed through a polarizing filter.
- Light also has properties of particles:
The photoelectric effect causes electrons to move and flow. Scientists think this is caused by tiny packets or particles of energy called photons.
many calculators use photovoltaic cells
The electromagnetic spectrum is the name for the range of EM waves as arranged by increasing frequency.
(See p. 636-637)
Radio waves: longest wavelength and lowest frequency (inverse relationship).
Microwaves: shorter wavelength than radio waves and greater frequency. Water molecules absorb energy from microwaves and cause food to get hot.
Radar: radio detection and ranging.
Infrared rays: “below red” can be used to keep food warm. Used to make a thermogram.
Visible light: is a narrow range on the EM spectrum that has a shorter wavelength and higher frequency than infrared.
ROY G BIV
Ultraviolet rays: “beyond violet.” Shorter wavelength and higher frequency than visible light.
Can damage skin and eyesight.
X Rays: very short wavelength. Higher frequency than UV rays.
Can penetrate most matter.
Gamma rays: shortest wavelength and highest frequency. Most energy and penetrating power of all EM waves.
Can cause serious illness!
Chapter 23
Light and Our World
When light strikes an object it can be reflected, absorbed, or transmitted.
Opaque objects absorb or reflect light. You cannot see through them! (wood, metal)
Transparent materials transmit light. Light passes through.
(glass, air, water)
Translucent materials scatter light as it passes through. You can not see details clearly!
(frosted glass, wax paper)
Regular reflection occurs when parallel rays reflect off a smoothsurface (mirror).
Diffuse reflection occurs when parallel rays reflect off a roughsurface in all directions.
3 types of mirrors: plane, concave, & convex mirrors.
Plane mirror is flat and shows a virtual image (behind & right side up), and same size as object.
Uses: Bathroom mirror
Concave mirrors curve inward (think of a cave opening) reflecting parallel rays to a focal point. rays
concave mirror
focal point
If an object is behind the focal point, a real image (inverted) is formed by reflected rays.
If an object is between focal point and mirror, a virtual image (behind mirror and upright) is formed. Uses: makeup mirror
Head lights, flashlights
Convex mirror curves outward reflecting parallel rays more spread out. The focal point is where the reflected waves appear to come. Always produce virtual image.
Uses: security mirror
cars, buses
Refraction and lenses:
Refraction is the bending of light rays as enter a medium at an angle.
(The new medium changes the speed of light-making it change direction).
- See a mirage
- rainbows
- Beakers filled with different media
A lens is a curved transparent material used to refract light.
Concave lens is thinner in the center than at the edges.
The rays never meet, so a virtual image is always produced.
Convex lens is thicker in the middle.
A real image is produced if object is beyond focal point.
A virtual image is produced if object is between lens and focal point.
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