P5.3 - Wave Interaction Flashcards
What is reflection?
Reflection is when a wave reverses direction upon meeting the boundary between two media.
What do all wave phenomena occur at?
All wave phenomena only occur at the boundary between two different media.
What is a medium?
A medium is a substance/material of the same particles.
What boundary does reflection occur at?
Reflection occurs at the air-glass boundary.
What is a ray diagram?
A ray diagram explains how and where mirrors (and lenses using refraction) form images of objects.
What is the normal line in ray diagrams?
The normal line intersects the mirror/lens boundary at exactly 90 degrees.
The normal line meets perpendicular to the boundary.
What is the incident ray?
The incident ray is a ray of light that comes towards the mirror/lens, the boundary.
What is the reflected ray?
The reflected ray is a ray of light that moves away from the mirror/lens having interacted with the boundary.
What is the angle of incidence?
The angle of incidence is the angle the incident ray makes with a normal.
What is the angle of reflection?
The angle of reflection is the angle the reflected ray makes with the normal.
What is a plane mirror?
A mirror which is perfectly flat and reflects back all the light incident upon it.
What is the law of reflection?
- The angle of incidence, i = The angle of reflection, r.
- Only true for plane mirrors.
What is refraction?
- Refraction is the change in direction of a wave when
its speed changes as a result of going from one
medium to another.
What happens as a wave crosses a boundary between two media?
- Refraction.
- As a wave crosses the boundary between two
different media, part of its wavefront changes speed
first. This results in the wave changing speed. Hence,
the direction of the wave changes and it is observed
to bend.
What do convex lenses do?
- Converge light rays.
- Make parallel rays passing converge
(focus) to a point. - Used in magnifying lenses, cameras forming an image
of an object, correcting long sight.
What do concave lenses do?
- Diverge light rays.
- Make parallel rays passing through it diverge
(spread out). - Used for correcting short sightedness.
What is the principal focus for lenses.
- The point where lights parallel rays meet or appear to
meet. - On both sides of the lens.
What is the focal length?
- The distance from the lens to the principal focus.
- Same focal length on each sides of the lens.
- The shorter the focal length the more powerful the
lens because it has refracted light rays more.
What happens in normal vision?
In normal vision, the eyes’ lenses focus rays of light onto the retina of the eye.
How do rays from nearby and distant objects travel?
- Rays from nearby objects appear to travel diverging to
each other. - Rays from distant objects appear to travel parallel to
each other.
Describe how short sightedness occurs and what type of lens fixes it?
- Eye lens is too powerful (refracts light rays a lot).
- Eyes can only focus light rays from objects nearby as
the light rays enter the eyes diverging. - Eyes cannot focus light rays from objects far away
onto the retina, instead focussing rays in front of retina
as light rays enter eyes travelling parallel. - A concave lens is used to diverge parallel light rays
before they enter the eyes.
Describe how long sightedness occurs and what type of lens fixes it.
- Eye lens is weak (refracts light rays a little).
- Eyes can only focus light rays from objects far away as
the light rays enter the eyes parallel. - Eyes cannot focus light rays from objects nearby
onto the retina, instead focussing rays ‘behind’ the
retina as light rays enter eyes travelling diverging. - A convex lens is used to converge diverging light rays
before they enter the eyes.
What is a real image?
A real image is an image that is formed where light rays meet.
What is a virtual image?
A virtual image is an image that is formed where light rays appear to come from.
What is an upright image?
An image which is the same way as the object.
What is an inverted image?
An image which is upside down compared to an object.
How do you calculate magnification on a ray diagram?
Magnification = Image height / Object height
What magnification indication image magnification and image diminishing.
- Magnification > 1 IMAGE MAGNIFIED
- Magnification < 1 IMAGE DIMINISHED
What image is produced when an object is placed outside the focal point/principal focus of a convex lens?
- Same type of image formed which happens in eye.
- Real.
- Inverted.
- Diminished.
What image is produced when an object is placed inside the focal point/principal focus of a convex lens?
- Same type of image formed in a magnifying glass.
- Virtual.
- Upright.
- Magnified.
What image is produced when an object is placed out the focal point/principal focus of a concave lens?
- Virtual.
- Diminished.
- Upright.
What do thicker lenses (given the same material have)?
Explain.
- Thicker lenses have shorter focal lengths.
- Light spends more time travelling through a
thicker lens, so will end up being bent more. - Shorter focal length means light converges more
for convex lenses and diverges more for concave
lenses.
What is dispersion?
Dispersion is the splitting of white light into its constituent wavelengths (spectrum).
Why does dispersion happen?
- Different wavelengths of EM radiation travel at
different speeds within glass, so refract by
different amounts. - The smaller the wavelength/the higher the
frequency, the more the
refraction.
What does it mean if an object appears only a certain colour in white light?
- If an object appears a certain colour under
white light, for example blue. - It is reflecting only that frequency (blue) and
absorbing all the other frequencies.
What does reflection from surfaces depend on?
- Reflection from surfaces depends on the type of
material. - Specular reflection produces sharp images, for
example a mirror. - Diffuse scattering produces no images, for
example a sheet of paper.
Why does milk appear white when ink appears black?
- Light can be scattered from particles.
- Milk appears white because its particles scatter
all wavelengths. - Ink appears black because its particles absorb all
wavelengths.
Why does the sky appear blue?
The molecules in the atmosphere are very small and scatter light with short wavelengths such as blue, which is why the sky appears blue.
What do filters do?
- Filters absorb certain frequencies of light but
transmit others.
Give an example of how a red filter works?
A red filter absorbs all the different frequencies of white light except the small band of frequencies that we call red.
Why does no light look get through a red and green filter put a few cm apart from each other?
- The red filter only transmits red light which the
green filter absorbs. - The green filter cannot transmit red light and
hence no light gets transmitted. - The no light ‘looks’ black
Explain why some clouds appear white, but some appear dark?
- White clouds scatter all/most wavelengths of light.
- Dark clouds absorb most wavelengths of light.
Why is a yellow fish black when a blue light is shone onto it?
The fish can absorb all the frequencies of light except the yellow which is reflects. However, the blue light does not contain the frequency for the yellow light to be reflected and hence the fish appears black.
Explain how a blue balloon can be both blue and black?
- Blue balloons reflect blue wavelengths of light,
under white light. - Red light contains only red light wavelengths.
- This, when illuminated by red light, the blue
balloon will absorb the red light and reflect
nothing, appearing black.
appearing black.
Suggest why you do not see a spectrum when white light goes through a rectangular glass block.
- A rectangular block has two lines of symmetry.
- Thus, the final refracted beam travels parallel to
the original incident beam. - Therefore, the different wavelengths of light within
the white light, aren’t separated out.
