Can you light a bulb with a battery and a wire?

[alkemyst]

He was a Havard professor. A rival.

 

[DrPizza]

That video is trying to copy another video that was out about 10-12 years ago. In the other video, the other students WERE from electrical engineering programs at one of the ivy league schools. That video shows several of the students saying you would need two wires, else a socket to screw the bulb into. There was a picture-in-picture of an engineering professor reacting to watching that video. That was used to convince science teachers to do two things:
A) Not assume students came to their class with the correct background knowledge.
B) Assume their students came to class with incorrect preconceptions & that those preconceptions are incredibly hard to break down.

As a pretest to circuits, I give students a variety of diagrams of circuits with lightbulbs. Only two students, ever, have correctly identified which bulbs will light and which ones won't. Yet, 100% of the students have heard of "complete circuits." Even at the college level, and even among engineering students, students believe that those two wires heading down from the filament in a lightbulb both connect to the little metal thing at the base of the lightbulb. The majority don't realize that the part that screws in serves two purposes - to hold the bulb, and as one side of the circuit. (My students do a lightbulb dissection lab as well. You should see the lights turn on (pun intended) when they realize how a bulb is wired.)

Cogman, if we had a much better video, I suspect what you'd see is that people try to touch one side of the battery and the wire to the bottom tip of the bulb - it's not that they're having trouble doing it in their hands. I've had 100's of students doing this with even more difficult scenarios; it's not that difficult. That professor's point is that these students obviously don't understand the concept of "complete circuit."

 

[Rubycon]

It's possible to illuminate a bulb with NO wire and NO dry cell. AAA, AA, C, D parts are dry cells NOT batteries! The most common batteries used by the consumer are 6V lantern cells and of course the 9V rectangular battery.

 

[TecHNooB]

That video is trying to copy another video that was out about 10-12 years ago. In the other video, the other students WERE from electrical engineering programs at one of the ivy league schools. That video shows several of the students saying you would need two wires, else a socket to screw the bulb into. There was a picture-in-picture of an engineering professor reacting to watching that video. That was used to convince science teachers to do two things:
A) Not assume students came to their class with the correct background knowledge.
B) Assume their students came to class with incorrect preconceptions & that those preconceptions are incredibly hard to break down.

As a pretest to circuits, I give students a variety of diagrams of circuits with lightbulbs. Only two students, ever, have correctly identified which bulbs will light and which ones won't. Yet, 100% of the students have heard of "complete circuits." Even at the college level, and even among engineering students, students believe that those two wires heading down from the filament in a lightbulb both connect to the little metal thing at the base of the lightbulb. The majority don't realize that the part that screws in serves two purposes - to hold the bulb, and as one side of the circuit. (My students do a lightbulb dissection lab as well. You should see the lights turn on (pun intended) when they realize how a bulb is wired.)

Cogman, if we had a much better video, I suspect what you'd see is that people try to touch one side of the battery and the wire to the bottom tip of the bulb - it's not that they're having trouble doing it in their hands. I've had 100's of students doing this with even more difficult scenarios; it's not that difficult. That professor's point is that these students obviously don't understand the concept of "complete circuit."

I had to wiki lightbulbs to see where the two terminals were. I figured it was similar to a DC jack like you typically see on laptops (in that it seems like there's only 1 contact).

 

[Cogman]

Cogman, if we had a much better video, I suspect what you'd see is that people try to touch one side of the battery and the wire to the bottom tip of the bulb - it's not that they're having trouble doing it in their hands. I've had 100's of students doing this with even more difficult scenarios; it's not that difficult. That professor's point is that these students obviously don't understand the concept of "complete circuit."

I guess I've just got too much faith placed in humanity. The concept of completing the circuit was something I figured out in the first grade. (Gizmos & Gadgets, That was a great game)

 

[Rubycon]

I had to wiki lightbulbs to see where the two terminals were. I figured it was similar to a DC jack like you typically see on laptops (in that it seems like there's only 1 contact).

There are so many different types of light bulbs as the term is quite vague.

The common lamp used in a flashlight or torch has a solder tip surrounded by a glass ring insulator and the body and flange is connected to the other side of the filament. Some lamps are bi-pin while others are axial with a wire on each side. (the common torchiere halogen lamp as well as many lamps used in vintage audio gear taking the same form as the bussman fuse are examples)

In my last post I used the common NE2 glow lamp as an example. You can even strip it of its leads and make it glow just by rubbing it on the back of cat on a dry day! No cat around? Try a rubber shoe. Or if it's too damp you can put it in a microwave. A 4W UHF handie talkie can also have sufficient ERP at its antenna to make it fire as well when keyed up.

 

[CZroe]

I had to wiki lightbulbs to see where the two terminals were. I figured it was similar to a DC jack like you typically see on laptops (in that it seems like there's only 1 contact).

What idiot has ever believed that a DC barrel connector was a single conductor?! When you "know" that there must be two terminals then you can easily FIND them. "Hmm. I wonder why the threading is always metallic, despite it making them sometimes stick in the socket."

Preconceptions or not, it doesn't take a genius.

 

[disappoint]

It's possible to illuminate a bulb with NO wire and NO dry cell. AAA, AA, C, D parts are dry cells NOT batteries! The most common batteries used by the consumer are 6V lantern cells and of course the 9V rectangular battery.

It's also possible to light a bulb with no wire, no dry cell and no batteries.

 

[us3rnotfound]

What the fuck, MIT graduates with problems of lighting a bulb with a wire. FUck.

 

[Cogman]

It's also possible to light a bulb with no wire, no dry cell and no batteries.

Microwaves are fun, aren't they

 

[Jeff7]

It's possible to illuminate a bulb with NO wire and NO dry cell. AAA, AA, C, D parts are dry cells NOT batteries! The most common batteries used by the consumer are 6V lantern cells and of course the 9V rectangular battery.

Lantern cell? Aren't 6V's 4 cells in series, thus being a battery?

 

[Rubycon]

Lantern cell? Aren't 6V's 4 cells in series, thus being a battery?

Yes you are correct. If you take one apart you will have four 1.5V cells which when wired in series provide the 6V at the spring terminals.

A four way 18650 lithium ion pile at 14.8V would be much better to run an SST90 via PWM.

 

[Jeff7]

Yes you are correct. If you take one apart you will have four 1.5V cells which when wired in series provide the 6V at the spring terminals.

A four way 18650 lithium ion pile at 14.8V would be much better to run an SST90 via PWM.

So when you called it a lantern cell......:sneaky:

"Aha, I've got you!"

</Monty Python>

 

[disappoint]

Microwaves are fun, aren't they

True, although what I had in mind was a fluorescent bulb and a tesla coil, but same concept.

 

[eLiu]

What the fuck, MIT graduates with problems of lighting a bulb with a wire. FUck.

Damnit, see my last post. The people who couldn't do it aren't from MIT; they're from Harvard! Not that I'm faulting Harvard (though it is nice to poke fun at Harvard...), since none of those students would have been engineers of any kind.

coxmaster: yep, it is commonly taught, but that doesn't make it any more correct. See below...

Minjin: Right but the students they were polling weren't engineering students. They could've been graduates of the divinity program or the business school for all we know. I don't even know what is taught in either of those programs, so I certainly cannot expect their graduates to know anything about engineering... even basic stuff. Which is why I was saying the whole video is completely pointless.

******** weeeeeeeeee time for an epic tangent **********

As for lift... I assume you're referring to something like this: http://warp.povusers.org/grrr/airfoilmyth.html

That is wrong in so many ways. For starters, Bernoulli's Eqn cannot be used in the way that they're using it when viscosity is a factor. What they have labeled as the "low pressure bubble" coincides with what is called a boundary layer, and the pressure in the boundary layer is the same as the pressure at the edge of the boundary layer (to first order). The boundary layer forms purely as a result of viscosity. The notion of a 'low pressure bubble' is misconceived; it's not like there's a region where the pressure is low, and everywhere else the pressure is high. Also the thing they call 'downwash' is not downwash at all; downwash is the effect responsible for what's called "induced drag."

It's kind of disturbing that even sites claiming to disprove the myth about lift only manage to introduce more errors.

Bernoulli does not play any effect in the generation of lift. At all. I don't need to know *anything* about Bernoulli and I can accurately calculate the amount of lift generated by an object. Like mass and energy, momentum is conserved. So you can draw a box (or a cube) around the wing (or airplane). Now measure the air's momentum coming in, and the air's momentum coming out of the box. The air has experienced some net change in momentum--which we know must be caused by a force*. By newton's third law, the wing or airplane will have experienced the opposing change. The component of this force in the direction of the plane's travel is the drag. The component of the force perpendicular to the plane's travel is the lift. Which is to say, if a plane is traveling "to the left," then the air behind it will have some downward direction (if the plane is generating lift).

The stuff below is more detailed than is really necessary... basically lift is all about momentum changes.

If someone asks you "how does a wing generate lift," you answer "momentum exchange with the atmosphere." The wing pushes on the air. The air pushes on the earth. Action and reaction. It's like jumping on a bed... you push down on the mattress, which in turn pushes on the ground.

Keep reading if you want to watch me try and stumble through a semester of undergraduate fluid mechanics in a few paragraphs, lol.
*Ok, so some of you might be wondering "what about pressure?" I've included pressure (defined as force acting over an area) in the general "force" category. If you count pressure & external forces separately, then depending on how you draw the box, the explanation for lift will be different. Say --- is my wing:
____
| |
| |
| --- |
| |
|___|
A narrow, tall box like that one will tell you that lift is from a change in momentum of the air. A box that is instead wide and short will tell you that lift is from top/bottom pressure differences. A box that's somewhere in between (like a square) will split the difference evenly. This is simply b/c pressure & momentum are intimately related.

Basically, the equation that describes the conservation of momentum goes something like this:
[change in momentum of the air in the box] + [momentum flowing out] - [momentum flowing in] = forces

But "forces" is often broken down into additional components... like force from viscosity (drag), forces from gravity, force from pressure, force from the engines, force from blahblah, etc. So if you let pressure be its own thing, then the only way the air can interact with the wing is through pressure. So you integrate (i.e., sum up) the pressure over every "point" on the surface of the wing, and that's the net force (from pressure) felt by the wing. (In 2D, that's all lift. In 3D, that's lift and a component of drag--this "induced drag" business I mentioned earlier.) Changing the shape of the "box" (called a control volume) changes how you are measuring what the wing feels--whether you're going after the momentum change of the air, or going after the pressure over the whole wing.

So whether you want to call it momentum, pressure, or both is all a matter of accounting. I like momentum b/c it's a nice, simple explanation.

Also, in practice, your box will have a hole in it to make the quantities actually computable... see page 2 here for a picture of what I mean:
http://ocw.mit.edu/courses/aeronaut...2005-spring-2006/fluid-mechanics/f09_fall.pdf

 

[Mike Gayner]

Salt is in the third aisle at the super market!

THis iS funnier than the ops video

Holy. Fucking. Crapola.

edit: LAWL I think The Flying Pig is in that video at 5:03.

 

[DrPizza]

The sad thing is that we allow people like that to vote in the US. The founding fathers were right when they set up the electoral college.

 

[pcgeek11]

They are graduates and can't complete THE most basic electrical circuit... Typical engineer.
I'll bet their mammy is proud of them!
"I went to college and all I learned was how to go to school."

 

[Cogman]

They are graduates and can't complete THE most basic electrical circuit... Typical engineer.
I'll bet their mammy is proud of them!
"I went to college and all I learned was how to go to school."

And thats what makes me sad

There are many students that go to college that get straight A's without learning a single thing. They have absolutely no ability to apply what they learned to any sort of situation. They do the "Learn it for the class, ignore it for everything else" approach of learning.

 

[TecHNooB]

What idiot has ever believed that a DC barrel connector was a single conductor?! When you "know" that there must be two terminals then you can easily FIND them. "Hmm. I wonder why the threading is always metallic, despite it making them sometimes stick in the socket."

Preconceptions or not, it doesn't take a genius.

It's more the location of the second conductor than the belief that there's only a single conductor. I'm also the type of person who will go against beliefs and say "really?" as opposed to "no you idiot, it goes like this." I think you are the latter.

 

[TallBill]

It's a stupid question to ask at graduation though. If you sat them down they would figure it out.

Hmmm, I specifically remember doing this in one of my very first physics classes. I'd have it lit up in 5 seconds without thinking. It isn't tricky at all, and it doesn't require much dexterity either.

 

[PlasmaBomb]

I can run a clock off a potato.

I can run one off an overclocked lemon.

 

[Cogman]

I can run one off an overclocked lemon.

I can run one by the presence of my awesomeness.

 

[PlasmaBomb]

I amuse myself some days

That is quite amusing...

 

[Modelworks]

There was a bar in a rural area where I grew up that was located about 2000ft from the towns AM radio station. The bar got the reputation as being haunted because one night during a power outage the neon signs for things like brands of beer took on an eerie glow and flickered while none of the other lights worked. The bartender even unplugged some of them and when it continued to glow when unplugged that really made it seem haunted.