ELECTROMAGNETIC WAVES Flashcards
1
Q
- What is light an example of?
A
- an electromagnetic wave (EM)
- it is self propagating
- it consists of oscillating electric and magnetic fields
2
Q
- How can light be shown?
A
- as a changing electric field that causes a change in the
magnetic field - or vice versa
3
Q
- What is a waving electric field?
A
- it is a field that causes similarly waving magnetic fields
to act - they act at right angles to the waving electric field
THESE OSCILLATING FIELDS:
- they have sinusoidal movement
- they travel through space at a fixed speed
- this speed is known as c
- this is the speed of light
4
Q
- When is a self-supporting process possible?
A
- when the electromagnetic wave propagates at a
certain speed - this speed is 299 792 458 m/s in a vacuum
5
Q
- What is the speed of light?
A
- 299 792 458 m/s
- it is of fundamental importance in physics
- it is the same for all observers
- this is regardless of direction or speed
6
Q
- How do we calculate the speed of light in a vacuum?
A
c = f . λ
c = speed of light (m/s)
f = frequency (Hz)
λ = wave length (m)
7
Q
- Electromagnetic waves have a large range of wavelengths.
What are the wavelengths for Visible light?
A
- it has a wavelength of between 380 nm and 750 nm
8
Q
- What are different frequency ranges in the spectrum generated by?
A
- they are generated by different physical processes
- they interact differently with matter
- they are given different labels
9
Q
- What is Refraction?
A
- this is when a ray of light is transmitted obliquely
- it is transmitted through a boundary
- this boundary is between two materials of unlike index
of refraction - this causes the ray to bend
OBLIQUELY= indirectly, slant wise
NB:
- the wave is changed
- the frequency is constant
- the wave length is changed
- this is due to the different speeds of light
- this is due to the different objects that the light pass
through
- these objects have different densities
10
Q
- How is the Absolute Index of Refraction calculated?
A
11
Q
- How do we calculate the relative index of the refraction of material 1 with respect to material 2?
A
- this is used for any two materials
- n1 and n2 are the absolute refractive indices
of the two materials
INDICES= a sign or measure of something
12
Q
- Within this equation, what happens when n2 is greater than n1?
A
- the ray will bend toward the normal
- it does this as it enters the second material
- ϴ1 is found between the incident ray and the ⟂
Normal Force - the ray bends towards the normal n2 material
- the n2 material is more dense
13
Q
- Within this equation, what happens when n1 is greater than n2?
A
- the ray will bend away from the normal
- n1 = incident
- n2 = refracted
- the ray will bend away from the normal
- n1 material is more dense
14
Q
- What happen when n1=n2?
A
- ϴ is the same when n1 = n2
- the ray continues to move in the same direction
15
Q
- What lies in the same plane?
A
- the incident rays
- the refracted (transmitted) rays
- the normal
16
Q
- What is ϴi?
A
- the angle of incidence
17
Q
- What is ϴr?
A
- this is the angle of refraction
18
Q
- What is Snell’s Law?
A
- this is the law that shows the way in which a ray
refracts - this ray refracts at an interface between materials
- these materials have indices of refraction ni and nr
19
Q
- How is Snell’s Law calculated?
A
20
Q
- What happens when light hits the surface of almost any material?
A
- some of the light will bounce back off of the surface
- this is known as Reflection
- this is how we are able to see objects
21
Q
- What happens when light falls on a smooth surface from a particular direction?
A
- the reflected light will also travel in a particular
direction - it will travel away from the surface
22
Q
- What is the Law of Reflection?
A
- this is when the reflected light leaves the surface
- it leaves the surface at the same angle that the
incident light falls on it
23
Q
- How do we calculate the Law of Reflection?
A
- incident 2 is equal to the reflective ϴ
24
Q
- In which two ways can reflection be described as?
A
- Specular
- Diffuse
25
25. What is Specular Reflection?
- this is what happens when light hits a surface
- this surface is:
- very flat
- reflective surface
- such as a mirror
ALL THE LIGHT COMING FROM A SINGLE DIRECTION:
- is reflected in a single direction
- parallel light rays will remain parallel after
reflection
- this is caused by a collision
26
26. What is Diffuse Reflection?
- this is when the light hits a rougher surface
- the light is reflected in a wide range of directions
27
27. What is Total Internal Reflection?
- it is the complete reflection of an incident light ray at
a boundary
- there is no transmission
28
28. When does the phenomenon of Total Internal Reflection occur?
- it occurs only for wave incidents on a boundary
- the boundary has a medium where the reflective
index is reduced
THERE IS NO TRANSMISSION RAY:
- when the refractive ray makes a 90° with the normal
force
29
29. What happens when the angle of incidence is larger than the critical angle?
- none of the wave is transmitted through
the boundary
- this is when only reflection occurs
30
30. Where is the Total Internal Reflection used?
- it is utilised in many optical devices
- it can hamper efforts to see into the parts of the eye
31
31. What can be said about the Refractive Index of Real Materials?
- it is not a constant for all the colours and the wavelengths of light
32
32. What is necessary for a material to be transparent?
- visible wavelengths of electromagnetic radiation must
pass through without being absorbed
33
33. Why do we see most objects in our environment easily?
- the transparency in the visible wavelengths is not very
common for solids
34
34. What happens to materials that transport to the visible light?
- they will generally absorb in the wavelength bands
- they are absorbed by these bands on either side
- this is both in the infrared and the ultraviolet side
35
35. What varies the refractive index of a material?
- it varies in a characteristic ways around the
wavelength bands
(infrared and ultraviolet)
- these bands are where absorption occurs
36
36. What does an increase in the refractive index at the blue end of the spectrum result in?
- the red end of the visible spectrum having a lower refractive index
37
37. What causes an increase in the refractive index at the blue end of the spectrum?
- being higher on the refractive index on the shorter
wavelength side
- being lower on the refractive index on the higher
wavelength side
38
38. What is Dispersion?
- this is when the wave speed is depended on the
frequency
39
39. What is Dispersive Media?
- these are materials that have a wave speed that is
depended on the frequency
40
40. What can be said about blue light?
- the blue light has a higher refractive index
- this will cause it to bend more
