4.6.2.2 Properties of Electromagnetic Waves 1

Question 1

What happens when a light ray enters a more optically dense medium?

Answer 1

• angle of incidence larger than angle of refraction as object is more optically dense causing its velocity to decrease as it passes through the more optically dense material so light ray bends towards normal as it slows down
• angle is smaller as if light is modelled as wave fronts the one side of wave front hits boundary for more optically dense medium first before the other part of the wave front causing it to change speed and direction - other side of wave front continues in same direction but this causes the whole wave to rotate

Question 2

What happens when a wave enters a medium at a right angle?

Answer 2

• if waves enter of leave the medium at right angles to surface (along normal) they do not change direction
• when waves approach along a normal the waves slow down as they pass into the glass
• however, the whole wave front slows down at the same time - that means that the waves do not change direction

Question 3

What is a wave front?

Answer 3

wave front is an imaginary line that connects all the same points in a set of waves

Question 4

Why does a wave change direction when passing from one medium to another?

Answer 4

• light waves about to move from air into glass
• velocity slows down in more optically dense medium
• when the first wavefronts start to move into glass the first parts/sides of the wavefronts moving into the glass slow down
• this causes those parts/sides of the wave fronts to get closer together
• their wavelengths get smaller
• other side of wavefront which has not yet hit boundary travels further distance in same amount of time due to it travelling at higher velocity
• this causes the wave fronts to change direction towards the normal and so the wave is refracted
• when waves speed up they change direction away from the normal

Question 5

What may different substances do with EM waves?

Answer 5

• different substances may absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength
• The material interacts differently for different parts of EM spectrum because the wavelengths (and frequencies) are different- some effects are due to differences in velocity

Question 6

What is refraction due to?

Answer 6

due to difference in velocity of waves in different substances

Question 7

What changes and doesn’t change when a waves wave speed changes?

Answer 7

• when a wave change wave speed its wavelength changes
• frequency always remains constant

Question 8

How can you tell that a wave is slowing down?

Answer 8

wavelength decreases and waves get closer together