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是什么让手电筒发光？

The Power of Circuits #sciencegoals

Have you ever wondered how a flashlight works?

Sure, it seems pretty simple…all you have to do is move a switch or press a button,

and…ta da!

The light comes on!

But what really makes the light go on?

Right you are, Squeaks!

It’s electricity that makes the light go on.

Well, the electricity in a flashlight comes from the batteries that are inside.

Electricity flows from the battery to a light bulb.

And when the electricity goes through the bulb, the flashlight lights up!

But the electricity doesn’t just jump from the battery right to the bulb.

In order to get from the battery to the light bulb, the electricity has to go along a specific path.

And that path is called a circuit.

If you listen to the word “circuit”, it kind of sounds like a shape you might know.

Let’s name some shapes, and see which one sounds like “circuit!”

Triangle…no…square…no…I know, circle!

And if you look at a circle, you can see that it goes around and around and doesn’t have

any spaces or gaps in it.

And that’s true of a circuit, too!

There can’t be any spaces in the path that electricity takes to get from a battery to

a light bulb.

In a circuit, if electricity doesn’t have a path to travel on, it stops.

It’s a little like a train on train tracks…when there’s no more track, the train stops.

So let’s see how a simple circuit works.

The battery is what we call the power source … that is, it’s where the electricity

comes from in this circuit.

Electricity flows from the power source on the path of the circuit.

And a lot of the time, that path is made by some kind of a wire.

The circuit then leads to whatever we want to power.

In this circuit, that’s a light bulb.

As the electricity goes through the bulb, the bulb lights up.

The electricity leaves the bulb, and flows back through the battery.

Then it follows the circuit all over again!

As long as there are no spaces in the circuit, the bulb will stay lit.

But what if we want to turn the light on and off?

Then we have to break the circuit, which means we need to put a space in it somewhere to

stop the flow of electricity.

So…we use a switch.

A switch allows us to make a space in the circuit if we want to.

When the switch is on, there’s no space in the circuit, and the light bulb is lit.

But when we move the switch off, we open up a space.

The electricity can’t jump over the space, so it can’t reach the light bulb…and the

bulb stays off!

Okay, so I’m going to try to build my own circuit using some of the parts that I have here.

I have a power source: this battery …

… and a wire for the electricity to travel through

…and a little light bulb.

If I arrange everything just so, it kind of looks like a circle!

But the bulb isn’t on.

That’s because I haven’t connected all of the pieces together.

Remember, there can’t be any spaces in the circuit.

So I’ll connect the wires to the power source…then I’ll connect one wire to the bulb…

And when I connect the other wire to the bulb and complete the circuit…the bulb lights up!

Now, I’m going to add something else to make it work more like our flashlight does.

I have this part that looks like a button.

And I’m going to put it right here.

And look!

The bulb is lighting up.

That means that there are no spaces in the circuit.

Okay Squeaks, I’ll press the button!

Hey, the light is off now!

That means that when I press the button, the circuit is incomplete…that means there’s

a space.

And when I let go of the button, the circuit is complete again.

The electricity from the battery can’t cross the space, so it can’t get to the bulb and

make it light up.

The button is a switch, kind like a switch on a flashlight!

If you look around, you’ll find that circuits just like this are everywhere, powering all

of the things around you!

Cars, trucks, and buses all use a circuit with a battery to get started.

And circuits run through your refrigerator, too, and in all of the other machines in your

home that use electric power in order to work.

Inside devices like phones and computers — which you’re using right now — there are very,

very small circuits that use the same basic set-up as the one I just built!

Large or small, it takes a circuit to carry the power we need to get going!

Thanks for joining us on SciShow Kids.

And special thanks to Google Making Science for helping us make this video!

Do you have a question about something?
(你可以)向大人寻求帮助 在视频的屏幕下方留言

to kids@scishow.com!

Thanks, and we’ll see you next time, here at the fort!

Crayon