Subtitles section Play video Print subtitles Greetings, fellow thinkers. I am Alessandro Volta, and today I invite you to join me on a journey of discovery. Together, we will relive my greatest triumph: the invention of the battery. But you say: "This doesn't look much like a battery!" Perhaps you were expecting: One of these. Or even: One of these. But my reply is this: All these batteries are the same and they only require one thing to make them work: A flow of electrons from high concentration to low concentration This simple idea powers flashlights, computers, and even tiny little helicopters! Come, meet my colleague Luigi Galvani. It is upon his research that I based my most important discovery. [singing] Frogs frogs frogs, you gotta cut them up to see how they work. [singing] Frogs frogs frogs, you gotta cut them up to see how they work. [off-screen] Galvani, how are you? Ah, Volta! Perfecto timing for a lab visit. I've just received an amazing new piece of equipment: A set of pinchers, where one part is made of copper and the other part is made of zinc and using these pinchers, I'm going to dissect the frog. Would you be so kind as to demonstrate for me? Gladly. Whoa, behold: electricity! From the tissues of this humble beast I've evoked electrical fire. Amazing. With this power, we could drive electric carriages and electric boats and if electricity resides in a single frog, we could feed one frog to another - and the second to a third and the third to a fourth - and make a gigantic frog full of fiery electric potential. Ah, but you're wrong my dear friend. You've made a magnificent discovery, but you misunderstand the cause. Well, where does the electricity come from? You're using tools that are made out of two different metals: Zinc and Copper This is the source of the current. If you were to use tools that were made of the same metal, nothing happens - see? But with my pinchers of zinc and copper, - Amazing, amazing! This is truly a wonderful discovery. Thank you, Volta. But now you've got me thinking: Why does electricity flow from one metal to another? What makes copper and zinc different? I'm so glad you asked. Let me tell you a tale: a tale of two metals, a tale about swimming, and a tale about cats and dogs. Here we have zinc, a metal that is made of dog-atoms. All of his dog-atoms love the ocean. They'd do practically anything to go for a swim in the salty water. And here we have his friend copper, who is covered in cats. All of his atoms are cats. They hate the ocean and want to get out of the water as soon as possible. Whenever a dog hops into the water, it has to leave two of its electrons behind. What am I going to do with all these extra electrons? And in order for a cat-ion to get out of the water, it's got to find two electrons. Cat-ions: Hey! Get us out of the water! We hate swimming! I want to help you, but I have no electrons. Cat-ions: But it's cold in here! Can't you get us dry without electrons? Nope. It takes two electrons to get you out of the water. But, let me call my friend Zinc. He may have extra electrons. [phone ringing] Hello? Zinc speaking. Zinc, it's Copper. Oh man, did you know I was just about to call you? Really? Hey, listen, can you do me a favor: do you and your dog-ions have any extra electrons around? That is so crazy! I was about to call you because I have all these dog-atoms, and every time they go swimming, they leave behind two electrons. Now I've got tons of electrons and I don't know what to do. Honestly, I'm feeling pretty negative about the whole situation. Well, I'm positive we can find a solution. Why don't you send a couple of electrons through the wire? That way I can pull some of my cat-ions out of the water. Right on, man. I'll send them through two at a time. [sound of electricity running through the wire] [purring] Oh, my cat's purring! It loves being out of the water. Hey, Zinc, have any more electrons? Totally! In this way, the two friends are able to share electrons through the wire, creating an electric current. The zinc dogs want to swim, the copper cats want to get dry, and that's what makes electricity flow through a battery. Here's the zinc, whose atoms are like dogs and want to swim. Here's the copper, whose atoms are like cats. Here's the wire through which Zinc sends its extra electrons to Copper. This flow of electrons is called an electric current. You can use that current to power a lightbulb, or a speaker. Or a frog's leg! Electrons flow from the zinc through the frog's leg and into the copper. The nerve in the frog's muscle is sensitive to electricity, and it flexes from the current. Now I understand! The electricity isn't generated in the frog's leg. Rather, electrons leaving zinc and traveling into the copper create the current. Yes! And if you want to make your own battery, all you need are: two kinds of metals, a wire, and something salty or sour. Here's one that I made. We have a zinc nail, a nice bit of copper, and this beautiful winter gourd. I am using it to power the tiny speaker here. [music] Oh, that's good. I made my famous batteries with zinc and copper, but other metals would work as well. Lithium batteries are in cellphones, and lead battereis are in cars. And instead of a gourd, you could try using really salty water or potatoes, or vinegar, or even ammonia. In every case, there's two metals: one that likes to go swimming, and one that likes to stay dry. And the difference between the two of them allows the electrons to flow. [sighing] Hey buddy, what's wrong? You made a wonderful discovery today! Yeah, I know. But I got totally wrapped up in the idea that we could use frogs fed to other frogs to power the world. And now I realize that the data say otherwise. And so, I guess I have no more need for these guys. Godspeed, Frogs. Adieu.