# 643: Ohm

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{{comic | {{comic | ||

| number = 643 | | number = 643 | ||

− | | date = | + | | date = September 30, 2009 |

| title = Ohm | | title = Ohm | ||

| image = ohm.png | | image = ohm.png | ||

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==Explanation== | ==Explanation== | ||

− | This | + | This comic is a play on the concepts of power as the human capacity to take action, and power as a strictly defined physical quantity, namely the amount of energy which flows from one locus to another in a unit of time. In calculus, this is expressed as dE/dt, hence the tooltip declaration that with great power comes great dEnergy/dt - though strictly speaking, great power EQUALS (is identical with) great dEnergy/dt. |

The saying references the comic-book superhero Spiderman. In various versions of Spiderman's origin story, teenager Peter Parker is being brought up by his Aunt May and Uncle Ben. Uncle Ben cautions Peter that "with great power comes great responsibility". Through an incident involving a spider and some cutting-edge technology, Peter Parker acquires spider-like powers - great strength and the ability to adhere to walls and ceilings. Parker fails to use his new powers to stop a mugging; it turns out that the victim is none other than Uncle Ben, who dies from injuries sustained. This failure to save his uncle haunts Parker and drives him to use his new powers for heroic purposes. Visually, the xkcd cartoon 643 recalls the dying Uncle Ben counselling his nephew to use his power responsibly. | The saying references the comic-book superhero Spiderman. In various versions of Spiderman's origin story, teenager Peter Parker is being brought up by his Aunt May and Uncle Ben. Uncle Ben cautions Peter that "with great power comes great responsibility". Through an incident involving a spider and some cutting-edge technology, Peter Parker acquires spider-like powers - great strength and the ability to adhere to walls and ceilings. Parker fails to use his new powers to stop a mugging; it turns out that the victim is none other than Uncle Ben, who dies from injuries sustained. This failure to save his uncle haunts Parker and drives him to use his new powers for heroic purposes. Visually, the xkcd cartoon 643 recalls the dying Uncle Ben counselling his nephew to use his power responsibly. | ||

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==Transcript== | ==Transcript== | ||

− | + | :[Ohm is holding his uncle by the shoulders.] | |

− | + | Uncle: Remember: With great power comes great current squared times resistance. | |

− | + | Narrator: Ohm never forgot his dying uncle's advice. | |

− | + | ||

{{comic discussion}} | {{comic discussion}} | ||

− | + | [[Category:Physics]] |

## Revision as of 01:48, 6 December 2012

Ohm |

Title text: More generally, with great power comes great dEnergy/dt |

## Explanation

This comic is a play on the concepts of power as the human capacity to take action, and power as a strictly defined physical quantity, namely the amount of energy which flows from one locus to another in a unit of time. In calculus, this is expressed as dE/dt, hence the tooltip declaration that with great power comes great dEnergy/dt - though strictly speaking, great power EQUALS (is identical with) great dEnergy/dt.

The saying references the comic-book superhero Spiderman. In various versions of Spiderman's origin story, teenager Peter Parker is being brought up by his Aunt May and Uncle Ben. Uncle Ben cautions Peter that "with great power comes great responsibility". Through an incident involving a spider and some cutting-edge technology, Peter Parker acquires spider-like powers - great strength and the ability to adhere to walls and ceilings. Parker fails to use his new powers to stop a mugging; it turns out that the victim is none other than Uncle Ben, who dies from injuries sustained. This failure to save his uncle haunts Parker and drives him to use his new powers for heroic purposes. Visually, the xkcd cartoon 643 recalls the dying Uncle Ben counselling his nephew to use his power responsibly.

Physical energy can exist in many different forms. In electrical physics, current flowing through a resistor generates heat. The basic units are defined such that the power (in Watts) converted into heat is given by the square of the electrical current flowing (in Amperes) multiplied by the reistance of the component (in Ohms). The unit, Ohm, is named for physicist Georg Ohm who determined experimentally that a given resistor would pass double the current when the electrical pressure (voltage) was also doubled.

The main cartoon text is therefore simply a statement that in electrical physics, when current flows through a resistor, the power dissipated is equal to the current squared, multiplied by the resistance.

## Transcript

- [Ohm is holding his uncle by the shoulders.]

Uncle: Remember: With great power comes great current squared times resistance. Narrator: Ohm never forgot his dying uncle's advice.

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# Discussion

"who determined that a given resistor would pass double the current..." -Actually, this is true only of ohmic resistors, which have constant resistance. Wire resistors, which I'm assuming are what Ohm used, are essentially ohmic for low voltage/current, but their resistance increases at high voltage because they give off dramatically more energy as heat. Other types of resistors have different behavior. For exmple, semiconductors have low resistance in one direction and high resistance in the other. Probably someone should correct this! Sciepsilon (talk) 01:51, 1 December 2013 (UTC)

- Somebody really should not. 108.162.219.223 06:34, 24 December 2013 (UTC)