Physics Flashcards
What are the four rules of reflection for both plane and curved mirrors?
- From the top of the object, through C (normal), which will reflect back over itself
- From the top of the object, parallel to the normal, then through F
- From the top of the object, through F, then parallel to the normal
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Define Reflection
The change in direction of a light ray when it bounces off a surface
Define Medium
The substance through which light travels
Define Ray
A straight line with an arrowhead that shows the direction in which a light ray was travelling
Define Incident Ray
A beam of light coming from a light source traveling towards the normal
Define Angle of Incidence
Angle measurement from the incident ray to the normal
Define Normal
A hypothetical line perpendicular to a surface (drawn from wherever the incident ray hits the surface
Define Reflected Ray
Beam of light travelling away from the surface (the reflected incident ray)
Define Angle of Reflection
Angle measurement from normal to reflected ray
Define Virtual Image
An image formed by rays that appear to be coming from a certain position, but are not actually coming from that position; image does not form a visible projection in a screen (“behind” the medium)
Define Real Image
An image that is formed when reflected rays meet
What are the properties of Light
Light travels
- in straight lines
- very fast (300km/sec)
- faster than sound
Why do we see things?
Objects reflect light into our eyes
In a rainbow, which colours have the longest and shortest wavelengths?
Red - longest wave length
Violet - shortest wave length
What is a concave mirror?
A reflecting surface curved inward
What is C?
The centre of curvature - the point in the circle where all normals will meet
What is the principal axis?
The horizontal normal that intersects with C
What is F?
The focal point - the point halfway between C and the mirror
Describe location and size - object is between F and the mirror
Upright and larger, virtual
Describe location and size - object is between C and F
Inverted and larger, real
Describe location and size - object is outside the center (past C)
Inverted and smaller, real
What is the first rule for concave mirrors?
Any line through C is a normal to the mirror (incident ray and reflected ray are the same)
What is the second rule for concave mirrors?
Any incident ray that is parallel to the principal axis will be reflected back through F
What is the third rule for concave mirrors?
Any incident ray that goes through F will be reflected back parallel to the principal axis
What four things have to be identified about a reflected image in diagrams?
- size (bigger or smaller)
- orientation (upright or inverted)
- distance from mirror (closer or farther away)
- real or virtual
What is a convex mirror?
A reflecting surface curving outwards
How do images in convex mirrors appear?
Upright and smaller than the object, ALWAYS VIRTUAL
How do convex mirrors reflect images?
Outwards
How do concave mirrors reflect images?
Inwards
Describe Refraction
The bending of light when the light passes from one medium to another
When does light bend towards the normal?
When going from a less dense medium to a more dense medium
When does light bend away from the normal?
When going from a more dense medium to a less dense medium
What is the first law of refraction?
The incident ray, refracted ray, reflected ray and normal all lie in the same plane
What is the second law of refraction?
Index of Refraction: ratio of speed of light in a vacuum to speed of light in a given medium
- passing from one medium to another, light bends and changes speed
What is “n”?
Index of Refraction
How does n correlate with density?
Directly - higher n = higher density
What is “c”?
The speed of light in a vacuum
What is the speed of light in a vacuum?
(3.00 x 10[8] m/s)
What is “v”?
The speed of light in a medium
What is the equation for n, c and v?
n = c/v
How does the index of refraction correlate with speed of light?
Inversely - increase in refractive index (and density) = decrease in speed
Is vacuum the least dense or most dense medium?
Least dense
As a beam of light becomes closer to being parallel to the surface of water, does more or less reflection occur?
More reflection - if the incident was along the normal, 100% refraction
Why do we see rainbows?
Because the speed of light changes when passing through raindrops
What is dispersion?
The process of separating colours by refraction of light through a prism
Why does a prism disperse white light into the spectrum of colours?
Each colour has its own wavelength and travels at a slightly different speed through the medium
What is the critical angle?
The angle at which the angle of incidence of a light ray produces a refracted ray along the surface of the medium
If an object is along the critical angle, do we see it?
No, the object is no longer visible
When does total internal reflection occur?
When the angle of incidence is greater than the critical angle, no refraction occurs
Why does light form just a circle on the surface when looking from underwater?
The light from overhead has a small angle of incidence and refracts to be visible to you. Light rays with higher angle of incidence than those will mostly reflect and will not be as visible
What is the appearance of a rainbow?
A multicoloured arc from red on the outer to violet on the inner
What causes rainbows?
Light is refracted entering the surface of the raindrop, reflected off the back of the drop and refracted as it leaves the drop, mostly from 40° to 42°; the amount of refraction depends on the wavelength of the light, hence its colour
What are the necessary conditions for a rainbow?
Water drops in the air and sunlight shining from behind at a low altitude angle
What is a lens?
A transparent object with at least one curved side that causes light to refract
What are the characteristics of lenses?
- Transparent
2. Either diverging or converging
What is a converging lens?
A lens that brings parallel light rays toward a common point as each ray refracts towards the normal when passing through the lens
What is a diverging lens?
A lens that causes parallel rays to spread away from a common point as each ray refracts towards the normal when passing through the lens
Where is the focal point for a converging lens?
the point on the principal axis through which the parallel rays converge
How is the focal point found for a diverging lens?
by tracing the diverging rays back to the principal axis
What is the diagram procedure for a converging lens?
- Draw a parallel ray from the top of the object to the centre of the lens, then it will refract/converge through F
- Draw a ray from the top of the object, through the center of the lens
- Draw a ray from the top of the object through the focal point on the object’s side to the centre of the lens, then it will refract parallel
What is the diagram procedure for a diverging lens?
- Draw a parallel ray from the top of the object to the centre of the lens, then it will refract/diverge as though it’s ray was passing through real F
- Draw a ray from the top of the object, through the center of the lens
- Draw a ray from the top of the object towards the focal point on the opposite side until the centre of the lens, then it will refract parallel
Describe the image with a converging lens - object is between F and the mirror
- farther from the lens
- upright
- larger
- virtual
Describe the image with a converging lens - object is between F and C
- farther from the lens
- inverted
- larger
- real
Describe the image with a converging lens - object is past C
- closer to lens
- inverted
- smaller
- real
Describe the image with a diverging lens
ALWAYS
- closer to the lens
- upright
- smaller
- real
What is chromatic aberration?
The fact that, with thick lenses, only rays near the principal axis will meet at the focal point
What is the difference between Galileo, Kepler and Newton’s telescopes?
Galileo - converging and diverging lenses
Kepler - only converging
Newton - REFLECTING TELESCOPE; did not suffer from chromatic aberration
Describe Galileo’s telescope
Converging lens as the objective lens, diverging lens as the eyepiece; low magnification but upright image
Describe Kepler’s telescope
Converging lens for objective lens and eyepiece; increased magnification but created inverted image
Describe Newton’s telescope
Light enters the telescope and travels to a concave mirror which reflects the light toward the focal point, then a plane mirror reflects towards the converging eyepiece
Describe Myopia
Near-sightedness: the eye focuses the image before it reaches the retina; the eye is too long and can’t see distant objects
Describe Hyperopia
Far-sightedness: the eye focuses the image behind/past the retina; the eye is too short and cannot focus on near objects
How is myopia corrected?
A diverging lens is used to separate the rays and make them focus on the retina
How is hyperopia corrected?
A converging lens refracts the rays to make them focus on the retina
