P3: Light Waves, Lenses Flashcards
Theories of light
- wave theory
- particle theory
- quantum theory
what is the quantum theory of light?
light is both particle-like as well as wave-like in nature
in the particle theory each (1)_________ is a (2)___________ of energy known as a (3)___________.
- wave pulse
- packet
- photon
what is a photon
a packet oe electromegnetic energy
general wave equation
1 - medium one
2- medium two
What is an angle of incidence?
The angle between the incident ray and the normal.
What is an angle of reflection?
The angle between the reflected ray and the normal.
what are the laws of refraction?
- The angle of incidence equals the angle of reflection.
- the ratio sin(i)/sin(r) is a constant for a pair of media
What are the laws of reflection?
- The angle of incidence equals the angle of reflection.
- the incident ray, reflected ray and the normal at the point of incidence are all on the same plane
What is a plane mirror?
A perfectly flat mirror.
What is a virtual image?
An upright and laterally inverted image.
How is a real image formed?
Focusing light onto a screen.
What is refraction?
The change of direction of waves when they travel across a boundary between 2 media of different optical densitities
What happens to a light ray when it travels from air to glass?
The angle of refraction is less than the angle of incidence. The ray travels towards the normal.
What happens to the speed of a light ray when travelling from glass into air?
it increases
What is diffraction?
The spread of waves when passing through a gap or round the edge of an obstacle.
How does the width of the gap effect the diffraction of waves?
The narrower the gap is, the greater the diffraction.
Why can radio and TV reception be poor in hilly areas?
If the radio waves do not diffract enough, the waves won’t reach the aerial on a house.
How does diffraction effect optical imaging?
If light diffracts too much, the image is of poor quality.
diffraction does not affect the (1)___________, (2) ______________, (3)_______________ , or the (4)________________ of light
- speed
- wavelenght
- period
- frequency
what is interference
phenomenon which occurs at a point where 2 or more waves superpose on each other to produce a combined vibration of amplitude lesser or greater any of the individual waves
constructive interference
phenomenon which occurs at a point where 2 or more waves superimpose in phase to produce a combined vibration of amplitude greater any of the individual waves
constructive interfrence occurs where 2 or more (1)_________ or (2)________ of transverse waves meet , or where 2 or more (3)_________ or (4)__________ of (5)__________ waves meet
- crest
- troughs
- compressions
- rarefractions
- longitudinal
destructive interference occurs where (1)_________ meets (2)________ of transverse waves meet , or (3)_________ meet (4)__________ of (5)__________ waves meet
- crests
- troughs
- compressions
- rarefractions
- longitudinal
displacement is a (1)_________ quantity and is the sum of the (2)________ of the individual waves being superposed. It can be (3)_________ or (4)___________.
- vector
- amplitude
- positive
- negative
two waves of amplitudes of 3mm are superposed in phase. The result is (1)___________ interference and the resulting amplitude is (2)____________
- constructive
- 6mm
two waves of amplitudes of 3mm are superposed in antiphase. The result is (1)___________ interference and the resulting amplitude is (2)____________
- destructive
- 0mm
Give four characteristics of a reflected image
- Objects are the same size
- Same distance away from the mirror
- The image is virtual
- Laterally inverted - left and right sides are swapped.
What is refraction?
The bending (changing direction) of a light ray as it travels from one transparent substance to another one with different optical density
What happens when a ray of light enters a more optically dense substance?
It bends towards the normal
What happens when a ray of light enter a less optically dense substance?
It bends away from the normal
Will a refracted ray ever bend beyond the normal?
No (so there is no bending when a ray crosses a boundary at a right angle)
What is the relationship between sin(i) sin(r) and the refractive index(η )
sin(i) / sin(r) = η
what does this image show?
the phenomenon of diffraction
What is Snell’s Law?
When an incident ray passes into a material: n = sin(i) / sin(r) When you divide sin(i) by sin(r) you get the same number (for a particular transparent substance)
in the diagram each wave that passes through the hole is being (1)____________. the lines represent the (2)____________ and the space between the lines represent the (3)___________. The phenomenon that occurs where the waves meet is called (4)_____________. Therefore determin what occurs at: A, B, C, D, E, F,
- diffracted
- cest
- troughs
- interference
A - destructive interference, B- constructive interference, C destructive interference, D- destructive interference, E- constructive interference, F- destructive interference
What happens when a ray of white light passes through a prism?
The white light emerges as a band of colours called a spectrum. This is caused because light is a mixture of colours and each colour travels through the prism at a slightly different speed, so each colour is refracted at a different angle. The prism has a different refractive index for each colour. This process is called dispersion.
What is total internal reflection used in?
Prisms in periscopes, binoculars and bicycle reflectors, optic fibres
When does total internal reflection happen?
When you go from a more optically dense object to a less optically dense object and when the angle of incidence is greater than the critical angle
Is looking through a magnifying lens real or virtual?
Virtual because the image looks bigger than it actually is.
3 things you need to say to describe an image properly:
- How big it is compared to the object.
- Whether it’s upright or inverted (upside down) relative to the object.
- Whether it’s real or virtual.
What is a luminous object?
Objects that emit their own light.
What are non-luminous objects?
Objects that just reflect light, this is the case for most objects.
How do optical fibres actually work?
Optical fibres are very thin strands made from two types of glass. The optically less dense glass surrounds an optically more dense glass. As the fibres are very narrow, light always strikes the boundary of the two glasses at an angle greater than the critical angle. All the light is reflected so no light escapes across the boundary, creating a ‘light pipe’. providing a path the light follows even when the fibre is curved
What is the critical angle (c) ?
The angle of incidence at which total internal reflection begins
What is the refractive index of a material?
The ratio of the sine of the angle of refraction and the sine of the angle of incidence. It tells you how fast light is travelling in a material
Describe an experiment to find the refractive index of glass
1) Draw around a rectangular glass block on a piece of paper and direct a ray of light through it at an angle. Trace the incident and emergent rays, remove the block, then draw in the refracted ray between them 2) You need to draw in the normal at 90° to the edge of the block, at the point where the ray enters the lock 3) Use a protractor to measure the angle of incidence (i) and the angle of refraction (r). Calculate the refractive index. Repeat to make the experiment reliable.
What is the speed of light?
300,000,000 m/s
What are the advantages of sending signals using optic fibres?
They are less prone to noise/heating They can send more information/data per second
identify the points of constructive and destructive interference
constructive interference: A, B, D, E
destrucitve interfrence: C, F
what kind of interference occurs at the following points in the diagram
- A
- B
- C
- D
- E
- F
- A - contructive interference
- B - constructive interference
- C - destructive interference
- D - constructive interference
- E - constructive interference
- F - destructive interference
separation of white light into its constituent colours is called ________
dispersion
how is a rainbow formed
water droplets in the atmosphere disperse white light into its constituent colours
what phenomenon does this image show?
dispersion of white light
What are the advantages of sending signals using optic fibres?
They are less prone to noise/heating They can send more information/data per second
what is the order of the visible spectrum of light seen on dispersion of white light
R O Y G B I V
red, orange, yellow, green, blue, indigo, violet
for total internal reflection to occur, the incident ray must approach from a medium of (1)__________ refractive index toward one of (2)_____________ refractive index, and its angle of approach must be greater than the (3)_________ angle
- greater
- lower
- critical
applications of total internal reflection
- telecommunications(cable tv , telephone, internet)
- diagnostic imaging (endoscopes)
- therapy -optical fibres used to direct laser beams to destroy tumors
what is the relation between critical angle and refractive index, when one of the media is air?
what is the relation between critical angle and refractive index, when one of the media is air?
name the following numbered terms
- the incident ray
- the normal
- angle of incidence
- refracted ray
- critical angle
- angle of refraction
- angle greater that critical angle
- internally reflected ray
a light ray travelled from a medium A to a medium B and was bent away from the normal. What can be said about medium B?
- B has a lower refractive index than A
- B is less dense than A
the incident angle is measured between the (1)____________ and the (2)__________. The angle of refraction is the angle measured between the (3)___________ and the (4)__________
- indicident ray
- Normal
- refracted
- normal
total internal reflection occurs when the (1)__________ approaches the less dense medium at an angle greater than the (2)________.
the critical anlge is that angle at which the (1)_______________ must approach the less dense medium to cause the (2)__________ to have an angle of refraction of (3)________
- incident ray
- refracted ray
- 90 degrees
which produces a stronger clearer image:
- a mirror
- a right angle isoceles glass prism
- a right angle isoceles glass prism
what is the critical angle of glass
42 degrees
definition of a lens
specially shaped transparent material than can form a focused images of objects
A (1)___________lens is one that is thicker at its centre and makes (2)_________ images by (3)_____________ parallel rays of light, while a (4)____________ lens is (5)__________ at its centre and produces (6)___________ images by (7)____________ parallel rays of light.
- convex
- real
- converging
- concave
- thinner
- virtual
- diverging
name the following numbered lens terminologies
- focal plane
- principal axis
- focal length
- principal focus
- optical centre
point at the centre of a lens through which all rays pass without deviation
optical centre
this imaginary line is perpendicular to the surface of a lens and passes through its optical centre
principal axis
a point on the principal axis where all parralel rays seem to converge
focal point
what happens to any ray that passes through the optical centre of a lens?
it passes though without deviation
the distance between the optical centre and principal focus
focal distance
The plane where the principal focus is located. It is perpendicular to the principal axis
focal plane
all parallel rays that pass through a lense will converge on the (1)______________, irrespective of the (2)_______________ at which they reached the lens
- focal point
- angle
what is magnification
the ratio of the size of the image to the size of the object
use the information from the diagram to write equations to calculate magnification
what is the lens formula for this system?
magnification = image/object = di/do
use the information from the diagram to write equations to calculate magnification
magnification = image/object = di/do
what is the lens equation for this system?
1/di + 1/do = 1/f
what is the general lens formua?
please note that before perfoming calculations : u, and v are given negative values if the image is virtual
f is given a negative value if the lens is concave
how do you know when an image formed by a lens is real?
- it can be displayed on a screen
- formed on the opposite side of the screen
- it is inverted
- formed by the convergence of rays
how do you know when an image formed by a lens is virtual?
- it cannot be displayed on a screen
- formed on the same side of the lens
- it is erect
- formed due the divergence of rays
examples of real images
- formed on the retina
- produced in a camera
- produced on cinema screen
examples of virtual images
- formed in a mirror
- that formed by convex magnifying glass
- images produced by concave lens
some images produced by concave lens:
- image formed from a concave pair of corrective glasses
characteristics of the image formed in a concave lens
- smaller than the object
- closer to the lens than the object
- erect
- virtual
characteristics of images formed in a convex lens
- on the opposite side of the lens from the object
- smaller or bigger(magnifying glass) than the object
- they are real or virtual(magnifying glass)
- they are inverted
what kind of lens is used to fix far sightedness(hyperopia)?
convex
what kind of lens is used to fix near sightedness(myopia)?
concave
the eyes contain what kind of lens
convex
which 2 parts of the eye act as lenses?
cornea
lens
this condition is called (1)_____________ and can be fixed using using corrective glasses than contain (2)____________
- myopia
- concave lenses
this condition is called (1)_____________ and can be fixed using corrective glasses that contain (2)____________
- hyperopia
- convex lenses
what kind of lens is this and why?
concave lense because the image is:
- same side as the object
- same orientation as the object (not inverted)
- smaller than the obect
- virtual (not on a screen)
what kind of lens is this and give the main reason
convex because:
the image is larger than the object
what does this animated image represent?
diffraction of waves and interference
