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The erstwhile Captain Kirk, who also had a stint playing a cop by the name of TJ Hooker, made the claim while hosting Have I Got News for You last month.
While referring to the arrival of the Olympic torch in Ilfracombe, he mispronounced the town's name, in what fellow guest Charlie Brooker suggested was a "deeply sexual manner".
Resistors also come rated to handle varying amounts of power— resistors rated for more power (more watts) are able to safely dissipate more heat generated within the resistor.
1/4 watt resistors are probably the most common, and are generally just fine for simple LED circuits like the ones we’re covering here.
So, 25 m A is the “desired” current— what we’re hoping to get when we pick a resistor, and also the and when we solve that we get: 1.2 V / 25 m A = 1.2 V / 0.025 A = 48 Ω Where “48 Ω” is 48 ohms.
(The units are such that 1 V/ 1 A = 1 Ω; one volt divided by one amp equals one ohm.
In practice, with AA alkaline batteries, if you drain it at 1000 m A, it will only last about 1/20 as long as it would if you drained it at 100 m A.
For higher than 500 m A, we should think about plugging into the wall. If we want to run one LED off of a 9 V battery, that means we have to take up a whopping 7.2 V with our resistor, which would need to be 288 Ω (or the nearest convenient value: 330 Ω, in my workshop).If you do a lot of electronics projects, you’re likely to have a bunch of resistors lying around.If you’re just getting started, you might want to get an assortment so that you have some handy.3 V (power source) – 1.8 V (LED voltage drop) = 1.2 V In this case, we’re left with 1.2 V which we’ll plug into our , which is current we want to drive the LED at.LEDs have a maximum continuous current rating (often listed as If, or Imax on datasheets). What this really means is that a typical current value to aim for with a standard LED is 20 m A to 25 m A—slightly under the maximum current. Running an LED near its rated maximum current gives you maximum brightness, at the cost of power dissipation (heat) and battery life (if you’re running off of batteries, of course.) If you want your batteries to last ten times longer, you can usually just pick a current that is only one tenth of the rated maximum current.