Light and Reflection
What is Electromagnetic Radiation? Waves that have an electric part and a magnetic part that oscillate perpendicular to each other.
What is the cause of EM Radiation? the acceleration of charged particles
How are EM Waves different from Mechanical Waves? They can move through a vacuum (they do not need a medium)
What is the Electromagnetic Spectrum? The range of frequencies that move at a speed of 3 x 108 m/s through empty space, divided into regions that describe their interaction with matter.
What determines the energy of mechanical waves? The amplitude
What determines the energy of electromagnetic waves? The frequency.
1.Wavelengths from 400nm to 700nm and frequencies around 1015 Hz visible
2.Wavelengths that can be used to create heat, by stimulating the motion of atoms that they strike microwaves
3.Penetrate all but the very dense part of the body, and are used medically quite often x-rays
4.Shortest wavelength and the greatest energy gamma rays
5.Wavelengths longer than visible light, and are responsible for warming the earth Infrared radiation
6.Used in tanning beds, often damaging skin cells Ultraviolet rays
7.The longest wavelengths of the electromagnetic spectrum radio waves
On what is the speed of EM waves dependent? The medium
Why do colors of objects change when looked at through other media, such as water? The medium slows the wave but frequency remains constant. Therefore wavelength decreases. Wavelength of light corresponds to color.
What is the frequency of EM waves that have a wavelength equal to the typical CD pit size of 1.2 m ( equals 10-6)?
v = f => f = v / = (3 x 108)/(1.2 x 10-6)= 2.5 x 1014 Hz
What is the wavelength of the waves produced by a coil that can generate a minimum frequency of 10.0 Hz?
v = f => = v / f = (3 x 108)/(10)= 3 x 107 m
What is the Principle of Least Time? Out of all possible paths that light might take to get from one point to another, it takes the path that requires the least time.
Reflection: Images Produced In Mirrors
The Law of Reflection: Light follows the same law of reflection as all other waves:The angle of incidence is equal to the angle of reflection.
NOTE: Both angles are measured from the normal to the surface at the point of incidence.
The Characteristics of Images
Type
/Real
/can be projected onto a piece of paper or screen
the focal point is in front of the mirror or behind the lens.
Virtual
/–cannot be seen on a piece of paper or screen
–the focal point is behind the mirror or in front of the lens.
–formed in locations where light does not actually reach
Orien-tation
/Inverted
/Upside-down
Upright
/Right-side Up
Size (Magni-fication)
/Enlarged
/Image is bigger than actual object
Reduced
/Image is smaller than actual object
Unchanged
/Image size is the same as the actual object size
Finding images in a plane mirror
Practice Questions:
How many wavelengths of an EM wave with a frequency of 5.20 x 1014 Hz can fit across a dot with a 0.2 mm diameter?
v = λf
3 x 108 = (λ)(5.20 x 1014 Hz)
λ= 5.77 x 10-7 m
Relative to the distance of an object in front of a plane mirror, how far behind the mirror is the image?
Equal!
Which kind of road surface is easier to see when driving at night, a pebbled uneven surface or a mirror-smooth surface?
Pebbled, uneven – no glare.
NotesLightBasics_2010KEY.doc