The Battery & Electromagnetism The key technologies in our story.
The Battery & Electromagnetism
⇐ Use this menu to view and help create subtitles for this video in many different languages. You'll probably want to hide YouTube's captions if using these subtitles.
- Consider the following experiment.
- You have two pieces of metal – copper and zinc –
- which you connect to conducting wires.
- And you then submerge the metals in an electrolyte –
- in this case vinegar.
- You will observe that bubbles will form
- around the zinc –
- but not on the copper.
- The metals seem dissimilar in this way.
- If you then connect the two wires holding the metals,
- something changes.
- Tiny bubbles begin to form around the copper terminal!
- It seems as though something is being pulled from the zinc,
- through the wire,
- allowing a reaction to occur on the copper side.
- And it turns out this is a flow of electrical charge,
- as electrons are pulled away from the zinc
- towards the copper
- through the conductive path in the wire.
- We can think of this flow
- as the result of a charge imbalance,
- or electrical pressure between the two metals –
- as compared to the instantaneous discharge observed
- with static electricity experiments.
- Towards the end of the 18th Century,
- Alessandro Volta had been investigating this effect.
- More importantly, he found chaining
- these cells together –
- would amplify this flow of charge.
- By 1800, he simplified things even further,
- removing the jar,
- which provided more electrolyte than was actually needed.
- He writes:
- "[using] a few dozens of small round disks of copper
- (pieces of coin for example)
- and [an] equal number of plates of zinc,
- I prepare circular pieces of spongy matter
- capable of retaining a water,
- "I continue coupling a plate of copper with one [of[ zinc,
- and always in the same order,
- and interpose between each of these couples
- a moistened disk.
- This continues until I have a column as high as possible,
- without danger of it falling."
- This is known, famously, as the "voltaic pile" –
- the first battery in history to provide
- a continuous flow of electrical charge – or current.
- More cells resulted in an increased
- electrical pressure at the two ends.
- And "electrical pressure" was an early term
- for what we now call "voltage" – after Volta.
- If the two leads of a voltaic pile were brought into direct contact,
- a series of shocks could be observed.
- At first, the utility of electric current
- as a communication method
- was not immediately obvious,
- aside from faint sparks and bubbles.
- One idea was to use the presence of bubbles
- to signal letters.
- The bubble telegraph used this method,
- though it involved 26 difference circuits – one for each letter.
- It was based on the fact that the battery providing the current
- can be placed at a distance,
- away from the jars containing
- the leads creating the bubbles.
- An inventive, although clumsy system,
- which was never adopted.
- But very soon, everything changed,
- after a famous demonstration in 1819.
- It was found that if we simply pass wire near a compass,
- and connect it to a battery,
- as soon as the wire made contact with the battery,
- the needle jumped -- without any physical contact!
- The only explanation was that
- the current-carrying wire was creating
- a temporary magnetic field!
- This was followed by a series of tests
- to figure out the direction of this field.
- First, we assumed it to be pointing along the wire with the current,
- or outwards from the wire as heat would travel.
- Eventually, it was determined that it must travel around the wire --
- in perpendicular circles.
- So a loop of wire would create a magnetic field
- which points through the center of the loop,
- and around the outside.
- This led to the galvanometer,
- which was designed to detect and measure electric current.
- It was simply a coil of wire with a compass needle in the center.
- When electric current was applied the magnetic field,
- the needle would always point
- perpendicular to the direction of the force,
- which was balanced on either side of the needle.
- The stronger the current,
- the stronger the deflection of the needle.
- By 1824, William Sturgeon demonstrated a way
- to increase the strength of this field even more.
- Simply by wrapping a coil of wire around a piece of iron,
- such as a nail, the magnetic force could be amplified.
- Iron seemed to be a better medium
- for supporting the formation of magnetic fields --
- in the same way that heat travels better through metal,
- than through air.
- We call this "permeability."
- And by wrapping the wire many times,
- the strength of the field could be amplified thousands of times.
- -- known as an "electromagnet."
- Suddenly, it was possible to create magnetic fields
- which could move needles with precision and force,
- using an electric current applied at a distance.
- 0:05:42.219,0:05:43.629 instantly, over a long distance was possible,
- 0:05:46.620,0:05:48.020 With these new technologies,
- the race to change the way the world communicates was on.
- What were we racing towards?
- At the time our understanding of information was in its infancy.
- People were thinking about information in a message
- as the number of letters in a message.
- So the goal was intuitive -- who could come up with
- the fastest way to transmit letters?
- To compare different inventions,
- we need standard measurements,
- so we can assume that everyone is using
- the same communication channel.
- A channel is just the pathway or medium
- through which our signals travel. In this case,
- it's a loop (or circuit) of wire.
- So, per circuit, who can transmit the most letters per unit of time
- Whoever had the fastest system would,
- therefore, reduce the cost per word/message
- for the sender using the system.
- A gold mine was waiting for whoever got there first.
Be specific, and indicate a time in the video:
At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
Have something that's not a question about this content?
This discussion area is not meant for answering homework questions.
Share a tip
When naming a variable, it is okay to use most letters, but some are reserved, like 'e', which represents the value 2.7831...
Have something that's not a tip or feedback about this content?
This discussion area is not meant for answering homework questions.
Discuss the site
For general discussions about Khan Academy, visit our Reddit discussion page.
Flag inappropriate posts
Here are posts to avoid making. If you do encounter them, flag them for attention from our Guardians.
- disrespectful or offensive
- an advertisement
- low quality
- not about the video topic
- soliciting votes or seeking badges
- a homework question
- a duplicate answer
- repeatedly making the same post
- a tip or feedback in Questions
- a question in Tips & Feedback
- an answer that should be its own question
about the site