ELECTROMAGNETIC WAVES

Question 1

1. What is light an example of?

Answer 1

• an electromagnetic wave (EM)
• it is self propagating
• it consists of oscillating electric and magnetic fields

Question 2

2. How can light be shown?

Answer 2

• as a changing electric field that causes a change in the
  magnetic field
• or vice versa

Question 3

3. What is a waving electric field?

Answer 3

• 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

Question 4

4. When is a self-supporting process possible?

Answer 4

• when the electromagnetic wave propagates at a
  certain speed
• this speed is 299 792 458 m/s in a vacuum

Question 5

5. What is the speed of light?

Answer 5

• 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

Question 6

6. How do we calculate the speed of light in a vacuum?

Answer 6

c = f . λ

c = speed of light (m/s)
f = frequency (Hz)
λ = wave length (m)

Question 7

7. Electromagnetic waves have a large range of wavelengths.
   What are the wavelengths for Visible light?

Answer 7

• it has a wavelength of between 380 nm and 750 nm

Question 8

8. What are different frequency ranges in the spectrum generated by?

Answer 8

• they are generated by different physical processes
• they interact differently with matter
• they are given different labels

Question 9

9. What is Refraction?

Answer 9

• 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

Question 10

10. How is the Absolute Index of Refraction calculated?

Answer 10

Question 11

11. How do we calculate the relative index of the refraction of material 1 with respect to material 2?

Answer 11

• 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

Question 12

12. Within this equation, what happens when n2 is greater than n1?

Answer 12

• 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

Question 13

13. Within this equation, what happens when n1 is greater than n2?

Answer 13

• 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

Question 14

14. What happen when n1=n2?

Answer 14

• ϴ is the same when n1 = n2
• the ray continues to move in the same direction

Question 15

15. What lies in the same plane?

Answer 15

• the incident rays
• the refracted (transmitted) rays
• the normal

Question 16

16. What is ϴi?

Answer 16

• the angle of incidence

Question 17

17. What is ϴr?

Answer 17

• this is the angle of refraction

Question 18

18. What is Snell’s Law?

Answer 18

• 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

Question 19

19. How is Snell’s Law calculated?

Answer 19

Question 20

20. What happens when light hits the surface of almost any material?

Answer 20

• 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

Question 21

21. What happens when light falls on a smooth surface from a particular direction?

Answer 21

• the reflected light will also travel in a particular
  direction
• it will travel away from the surface

Question 22

22. What is the Law of Reflection?

Answer 22

• this is when the reflected light leaves the surface
• it leaves the surface at the same angle that the
  incident light falls on it

Question 23

23. How do we calculate the Law of Reflection?

Answer 23

• incident 2 is equal to the reflective ϴ

Question 24

24. In which two ways can reflection be described as?

Answer 24

1. Specular
2. Diffuse

Question 25

25. What is Specular Reflection?

Answer 25

- 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

Question 26

26. What is Diffuse Reflection?

Answer 26

- this is when the light hits a rougher surface - the light is reflected in a wide range of directions

Question 27

27. What is Total Internal Reflection?

Answer 27

- it is the complete reflection of an incident light ray at a boundary - there is no transmission

Question 28

28. When does the phenomenon of Total Internal Reflection occur?

Answer 28

- 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

Question 29

29. What happens when the angle of incidence is larger than the critical angle?

Answer 29

- none of the wave is transmitted through the boundary - this is when only reflection occurs

Question 30

30. Where is the Total Internal Reflection used?

Answer 30

- it is utilised in many optical devices - it can hamper efforts to see into the parts of the eye

Question 31

31. What can be said about the Refractive Index of Real Materials?

Answer 31

- it is not a constant for all the colours and the wavelengths of light

Question 32

32. What is necessary for a material to be transparent?

Answer 32

- visible wavelengths of electromagnetic radiation must pass through without being absorbed

Question 33

33. Why do we see most objects in our environment easily?

Answer 33

- the transparency in the visible wavelengths is not very common for solids

Question 34

34. What happens to materials that transport to the visible light?

Answer 34

- 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

Question 35

35. What varies the refractive index of a material?

Answer 35

- it varies in a characteristic ways around the wavelength bands (infrared and ultraviolet) - these bands are where absorption occurs

Question 36

36. What does an increase in the refractive index at the blue end of the spectrum result in?

Answer 36

- the red end of the visible spectrum having a lower refractive index

Question 37

37. What causes an increase in the refractive index at the blue end of the spectrum?

Answer 37

- being higher on the refractive index on the shorter wavelength side - being lower on the refractive index on the higher wavelength side

Question 38

38. What is Dispersion?

Answer 38

- this is when the wave speed is depended on the frequency

Question 39

39. What is Dispersive Media?

Answer 39

- these are materials that have a wave speed that is depended on the frequency

Question 40

40. What can be said about blue light?

Answer 40

- the blue light has a higher refractive index - this will cause it to bend more