8. Light and lenses Flashcards
What type of waves are electromagnetic waves?
Electromagnetic waves are transverse waves that consist of an oscillating electric field and an oscillating magnetic field.
What is the equation for the speed of light?
c=fλ
c= speed of light in a vacuum (also air)
f= frequency
λ= wavelength
What is the electromagnetic spectrum, and what types of waves does it include?
The electromagnetic spectrum is the range of frequencies and wavelengths found in EM waves.
The EM spectrum includes, from lowest to highest energy: radio waves (long wavelength, low frequency, low energy), microwaves, infrared, visible light, ultraviolet, x-rays, and γ (gamma)- rays (short wavelength, high frequency, high energy)
What are the boundaries of visible light?
The visible spectrum runs from approximately 400 nm (violet) to 700 nm (red).
True or false: light waves are longitudinal because the direction of propagation is perpendicular to the direction of oscillations
False. Light waves are transverse because the direction of propagation is perpendicular to the direction of oscillation.
Key Concept: Transverse waves have particle oscillations perpendicular to the direction of propagation and energy transfer. Longitudinal waves have particle oscillation parallel to the direction of propagation and energy transfer.
In light optics, what is the definition of rectilinear propagation?
It means light travels in a straight line.
In optics, what is the definition of reflection?
Reflection is the rebounding of incident light waves at the boundary of a medium.
What is the definition between a real and a virtual image?
Real image: converges at the position of the image
Virtual: only appears to be coming from the position of the image but does not actually converge there.
A distinguishing feature is that real images can be projected onto a screen.
Real images are always upside down.
Virtual images are always upright.
In spherical mirrors, name and define:
(C) Center of curvature
(f) focal length)
(O) distance
(i) distance between object and mirror
Center of curvature (c)= a point on the optical axis which is the center of curvature would be the center of the spherically shaped mirror if it were a complete sphere. (i.e. center of ball)
Focal length (f)- this between the focal point and the mirror. For all spherical mirrors, f=r/2 where the radius of the curvature (c) is the distance between c (center of curvature) and the mirror
O= Distance between the object and the mirror
i= distance between the image and the mirror
(Equation) What is the equation for distance between objects and images in mirrors (convex/concave)
o= distance between the object and the mirror
i= distance between the image and the mirror
r= radius of the curvature
f= focal point
What type of images do concave mirrors create?
Concave Mirrors:
a. real, inverted
or
b. virtual, upright
Convex Mirrors: Virtual, upright
What type of images do convex mirrors create?
Convex Mirrors: Virtual, upright
Concave Mirrors:
a. real, inverted
or
b. virtual, upright
True or False: Real images can be upright or inverted
False: real images are always inverted.
Virtual images are always upright
What is a converging and diverging mirror?
Concave= converging
Convex= diverging
(Equation) What is the equation for magnification?
m= magnification (unitless)
i= distance between image and the mirror
o= distance between the object and the mirror
note the negative sign
When the image is less than than the object distance, the object is minimized. When the image distance is greater than the object distance, the object is magnified.
magnification
| m |>1 indicates magnification
magnification
| m |<1 indicates minimization
m |> 1 indicates
What will positive and negative values of the following tell you with mirrors?
o=
i=
r=
f=
m=
True or False:
The focal length of converging mirrors (and converging lenses) will always be negative. The focal length of diverging mirrors (and diverging lenses) will always be positive.
False:
The focal length of converging mirrors (and converging lenses) will always be positive.
The focal length of diverging mirrors (and diverging lenses) will always be negative
What is the mnemonic to remember some rules about mirrors?
UV No IR
UV= Upright images are always virtual
No= No image is formed when the object is a focal length away
IR= Inverted images are always real
What are the three rays that you need to draw for a ray diagram for concave or converging mirror?
- Parallel to axis, reflects back through focal point
- Ray to center of mirror, reflects back at same angle
- If the rays diverge, then draw the arrows on the other side of the mirror going up.
What is the definition of refraction?
It is the bending of light as it passes from one medium to anther.
Real World: When a pencil (or any straight object) is dipped into a glass of water at an angle, it looks impossibly bent where it intersects the surface of the water because the light reflecting off of the portion of the pencil under water is refracted
What is the speed of light?
speed of light= 3.00 x 10 8 m/s
FYI Speed of sound is 343 m/s
What is snell’s law, or the law of refraction?
Snell’s law (the law of refraction) states that there is an inverse relationship between the index of refraction and the sin of the angle of refraction (measured from the normal).
(Equation) What is the equation for the index of refraction of a medium
n= dimensionless quality called the index of refraction of the medium
c= speed of light in a vacuum
v= speed of light in a medium
FYI: to give context, the index of refraction of air is 1
(Equation) What is the equation to determine the angle of light rays when they pass from one medium to another?
n1 sinӨ1= medium from which the light is coming
n2 sinӨ2=Medium into which the light is entering
n= you get this value from equation of speed in a medium (n=c/v)
You measure the angles in relation to the ‘critical angle’ down the middle
What happens when a light enters a medium with a higher or lower index of refraction?
Higher: bends toward the normal
Lower: Bends away from the normal
Normal is a vertical line down the middle
What is the definition of total internal reflection?
Total Internal Reflection: a phenomenon in which all the light incident on a boundary is reflected back into the original material, which results with any angle of incidence greater than the critical angle, Өc.
Total internal reflection occurs when light cannot be refracted out of a medium and is instead reflected back inside the medium.
This happens when light moves from a medium with a higher index of refraction (like water) to a medium with a lower index of refraction (like air) with a high incident angle.
How do you draw a ray diagram for lenses (Convex)?
- Draw one ray parallel to the axis, and then have it refract through the focal point on the other side
- Draw another ray from the object straight through the center of the lens
- The point where they meet is the image. If they diverge, draw the rays in the opposite direction
(this is the opposite of what it seems like it should be)
How do you draw a ray diagram for Concave lenses?
- Draw a ray parallel to the axis, and then have it reflect away from the focal point.
- Draw another straight line right through the center of the lens.
- Backtrack if they diverge.
(this is the opposite of what it seems like it should be)
What is the SIR BIR BUV acronym for lenses (Convex)?
SIR: Smaller, Inverted, and Real
Bir: Bigger, inverted, Real
BUV: bigger, upright, and virtual
(Equation) What equation do you use for magnification and distance between objects for lenses?
It’s the same for mirrors.
o= distance between the object and the mirror
i= distance between the image and the mirror
r= radius of the curvature
f= focal point
m= magnification (unitless)
i= distance between image and the mirror
o= distance between the object and the mirror
(Equation) What is the equation for the power of a lens?
P=power of lens
f= focal length
(Equation) what is the equation for focal length when you add multiple lenses together?
What are the differences between the symbols of O, I R, F, and M between mirros and lenses (positive and negative)?
All are same, except I, R, and F are opposite
True or false: incident angle is always measured with respect to the normal.
True. In optics, incident angles are always measured relative to the normal.
Normal is the vertical slot
What is dispersion? What is aberration?
Dispersion: Dispersion is the tendency for different wavelengths of light to experience different degrees of refraction in a medium, leading to separation of light into the visible spectrum (a rainbow).
Aberration: Aberration (spherical or chromatic) is the alteration or distortion of an image as a result of an imperfection in the optical system.
What is diffraction?
Diffraction is the bending and spreading out of light waves as they pass through a narrow slit.
What is the slit lens system?
If you put light through a narrow opening, there will be several fringes.
The central maximum or central fringe is the brightest (maxima).
Diffraction may produce a large central light fringe surrounded by alternating light and dark fringes (minima) with the addition of a lens
What is the interference of light?
Interference: when waves interact with each other, the displacement of the waves add together in a process called interference.
Bridge: light is similar to other waveforms; it is affected by constructive and destructive interference when light passes through a slit and a lens, and when light passes through multiple slits. Interference also occurs with sound waves.
What is polarized light?
Polarized light is light where the electric field is only oscillating in one direction (up/down, or side to side, or diagonally)
Most light is not polarized, including that from the sun and lightbulb.
What is plane-polarized light?
In plane-polarized light, all of the light rays have electric fields with parallel orientation
One of the most common applications of plane-polarized light on the MCAT is in the classification of stereoisomers, as discussed in chapter 2 of organic chemistry. The optical activity of a compound, due to the presence of chiral centers, causes plane-polarized light to rotate clockwise or counterclockwise by a given number of degrees relative to its concentration (its specific rotation.
What is circularly polarized light?
In circularly polarized light, all of the light rays have electric fields with equal intensity but constantly rotating direction.
Circularly polarized light is created by exposing unpolarized light to special pigments or filters.
