How was Light's Speed Measured? A Detailed Explanation // HSC Physics

⌚Timestamp
00:00 Overview
00:57 Romer's observation of Io's orbital period
08:00 Stellar aberration (Bradley)
10:18 Fizeau's rotating toothed cogwheel
12:43 Foucault's rotating mirro
14:46 Rosa & Dorsey's calculation using electric and magnetic constants
16:00 Laser interferometry
17:21 Relationship of light's speed with distance and time

📚Syllabus
• conduct investigations of historical and contemporary methods used to determine the speed of light and its current relationship to the measurement of time and distance (ACSPH082)

[AngusMcAlister]

Thanks for making this video public. Must say, I am dreading this syllabus point!

[Rambo-xrsp]

Amazing explanation, keen to see the upcoming videos!

[MeeTerra]

18:13
> the definition of 1 second is the time taken for light to travel c metres
This is a circular definition, which would allow the quantities of a metre and a second to vary arbitrarily as long as they varied in the same proportion.

The second [...] is defined by taking the fixed numerical value of the caesium frequency, ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9192631770 when expressed in the unit Hz. (Wikipedia)

[shmkrar]

Thank you so much for the simple explanantions!

[programmingforfun]

Shouldn't the mirror be pushed back by 1/4 of wave length? So the total distance it will travel is 1/2 wave length longer than the other one.

[quangtruongta]

Tôi có suy nghĩ dùng cuộn phim chụp ảnh, cho quay với tốc độ cao, thay cho bánh răng và dùng hệ thức t1=t2=S1/v1=S2/v2 để tính vận tốc ánh sáng.

[pinakidas]

the Roemer thing is explained wrong! you cant observe both immersion AND emergence at the same time.

[Dietcokeml]

5:42 isn't the diagram on the left the true orbital period, and the shortest orbital period would actually be when the Earth is moiving towards Io?