New 15Apr2025. Updated 16Apr2025. This note is in group Technology. It would basically contain single notes that I would not know where else to add.
A. Electromagnetic wave’s presence before the current
The chapter
Fig. 1 – p12 (detail) of the «Electronics» book (1993) (Press for Fig. 2) Observe that an electromagnetic wave only with the best of imagination may be thought of as similar to a metal disc wave!
See Electromagnetic wave’s presence before the current on Stack Exchange: Physics. Posted by me 14Apr2025. My initial question goes like this:
| In Electronics (1993, written by Roger Bridgman in association with The Science Museum, London) I read on the two pages «Electromagnetic waves» (pp 12-13) that:
WAVES MAKING THINGS HAPPEN. When a metal disc strikes a closely packed and firmly held line of discs, a loose one at the far end shoots off. A pressure wave in the metal, travelling much faster than the moving disc, carries its energy down the line. In a similar way, when a bulb is connected to a battery, an electromagnetic wave tells the bulb to start glowing long before any electrons from the battery get there. I was so surprised to read this that I have been staring at that text over and over again. I have a feeling this is right, but is it? Let’s say we have 1 Volt battery and 1 Ohm bulb and 1 cm distance (if it’s relevant), what might that electromagnetic energy be like? Now if we replace «lamp» (=resistor) with «capacitor», I guess one could say that the electric field is set up «first», then according to Q = C * U = I * t the capacitor is supplied slowly with current. Is this along the same line of thought? |
The answers are certainly worth a read! Also the references given by the respondents. They would be to Veritasium and AlphaPhoenix YouTube channel lectures.
Fig. 3 – The cover of this «aluminium mirror»-like hard to photograph book