- [Narrator] Are you feeling curious?

- Isn't that awesome?

- [Narrator] Today on Curious Crew - Ultraviolet light, it's energizing.

We investigate a hot topic.

Solar cells are not all the same.

Exploring how light converts to electricity.

Solar energy, we're just heating up.

- [Narrator] Support for Curious Crew is provided by MSU Federal Credit Union.

Offering a variety of accounts for children and teens of all ages, while teaching lifelong saving habits.

More information is available at msufcu.org.

Also by the Consumer's Energy Foundation, dedicated to ensuring Michigan residents have access to world-class educational resources.

More information is available at consumersenergy.com/foundation.

Consumer's Energy Foundation, supporting education and building sustainable communities in Michigan's hometowns.

And by viewers like you.

Thank you.

(pop music) - Hi, I'm Rob Stevenson.

And this is, - [Children] Curious Crew.

- Welcome to the show everybody.

We always like to start every episode with a couple of discrepant events.

Because discrepant events stimulate - [Children] Curiosity.

- That's exactly right.

And I've got some fun ones for you today.

In fact, the first one I'm gonna show you is hidden underneath this towel, right here.

I have it hidden on purpose.

I have a very special glass globe, that I'd like you to start observing closely.

I want you to look at this very closely.

And Aida, what do you notice about this?

- That one side is black and the other side is silver.

- Okay, great.

So you can see that there's those veins in there and one side is black and one side is silver.

Now here's where it's gonna be fun.

I'm actually going to turn on this lamp and we're gonna observe what happens to that little globe, that actually doesn't even take very long before it reacts to it, which is really interesting.

So you're noticing it's picking up speed, like crazy.

Which is really fascinating.

So then I have another wondering and Ian I'm gonna ask you this one.

What do you think will happen if I turn off the light?

- Will it slow down or stop?

- Let's find out.

So I'm gonna turn off the lamp and let's see what sort of effect this has on the globe.

Now, in fact, it is starting to slow down.

It does take a moment to slow down because there's so much momentum going on in there that it's still spinning like crazy.

but it is beginning to slow down, which I think is really interesting.

Now I gotta tell you what this is called.

You may have seen one of these.

Some people have them on as decorations in their house, or on their desk or around a window sill.

This is called the crookes radiometer.

And it was invented back in 1873 by Sir William Crookes.

He was trying to do some different experiments and he ended up making this.

And he never really understood how it worked or why it worked, but he thought it was cool.

So he started selling it as a toy.

(laughing) So these have been around a really long time, but to understand how it works I'm gonna need some help from you guys, actually.

Now I'm gonna set that aside for another moment and I'm gonna bring in my fun little grasshoppers.

I've got these really cute little grasshoppers that I have right here.

And again, I'm gonna turn on the light and watch what happens when I turn on the light.

(buzzing sound) (laughing) Come on back.

Don't go away.

Don't leave, don't leave.

Now, watch what happens when I turn it off and turn it on and turn off and on and off.

(laughing) Okay, so I've got a couple of interesting phenomena here that I'm gonna ask you guys to be thinking about.

And in fact, I'd like three of you to think about this through the show, do a little scientific modeling and see if you can explain how these two things work.

Who'd like to do a little scientific modeling today?

A little modeling moments who wants to try that?

Okay, let's see it's gonna be okay.

Kah'riece, Julia, Aida, you guys are gonna be doing a little modeling moments today, which will be fun.

So does anybody have a guess what we're gonna be talking about today?

What do you guys think?

What do you think?

Chris what do you think?

- Solar energy.

- That's right.

We're talking about solar energy today.

Good job.

You might have been thinking about that because the solar panels here, that's really good thinking Chris.

Now, in fact, we're in a studio today.

So we're having to simulate that solar energy with an electric lamp or studio lights.

But of course I could take these things outside and I can make them work without electricity, which is pretty amazing, stick around maybe you can figure out the answers to these discrepant events too.

(pop music playing) - Let's see if we can figure out the discrepant event.

- The radiometer was interesting but I don't understand how it can move without a motor.

- I know, but the grasshopper had a solar cell on the back, but the radiometer didn't.

- But did anyone noticed the two different color sides of the blade?

- I saw that too, but I wonder how the color difference makes the blade spin.

(pop music) - [Narrator] Our sun produces light energy that travels to the earth.

Some of that light we can see, while others, like ultraviolet and infrared light, we can't.

But it is that energy that makes it possible for all living things on earth to survive.

Plants convert that energy into sugars, for food to grow.

And we use that energy to stay warm.

The sun's energy is also responsible for the water cycle on the planet, And even the wind we feel every day.

Scientists and engineers continue to think of clever ways to capture energy from the sun to make our lives better.

(gentle music playing) (electrifying music playing) (pop music playing) - Now weren't those discrepant events interest in you guys?

but Callan, I've got question for you.

What is the first thing you think of when I say solar energy?

- Heat from the sun.

- Okay that actually makes a lot of sense.

Now I'm inside right now.

And so I can't take advantage of solar energy but I can take advantage of light energy.

And in fact, I'm gonna turn this lamp off.

I've had this lamp going back here for a few minutes and you might notice I've got two pieces of paper and one is black, one is white.

And I also have those cups.

There's one, that's black, one that's white.

And I have thermometers all over, in the cups and on the paper.

Now I'm curious, which paper do you think is gonna get hotter Callan, is it gonna be the black paper or the white paper?

- I think it's gonna be the black paper.

- You are absolutely correct.

In fact, when I started this little experiment, they were all at exactly the same temperature.

But now the black paper is much, much hotter.

Now let's think about why that's so.

So we know that black paper is gonna be absorbing a lot of the wavelengths from light energy and reflecting very little.

And so much of that energy is gonna get converted into heat, which then we can actually feel and measure with the thermometer.

Whereas the white paper that actually reflects a lot of that energy.

So here's an example.

Callan have you ever walked on blacktop or concrete barefooted?

- Yeah.

- What was that like?

- The blacktop was a lot hotter, and the concrete wasn't as hot.

- Okay, great.

So you know the area then, around the black papers probably warmer.

So let me ask you a question, Ian.

What do you thinks happening to the air around the black paper right now?

- Well, because the black paper is hotter, I'm pretty sure that all the air particles are going quicker and quicker and moving really fast.

- Exactly, so we've got that transfer of energy.

So those air particles are moving faster.

They're bumping into things.

And in fact, we can look at this in another way, with one of my greatest toys called the solar balloon.

Ian, have you ever seen a solar balloon before?

- I don't think so.

So I actually have a solar balloon, here in the studio but it's already floating.

I'm gonna need some help to get this down.

Guys, can you lower that for me?

(pop music) Isn't that awesome?

This is a solar balloon, and in fact I've even used this outside.

It's absolutely amazing.

But think about what's happening because it's black, we can get that energy transfer from the light, from the sun or from the studio lights, and actually get that energy absorbing inside.

And it starts to excite those air particles.

So they start moving around more rapidly.

They're bumping into the plastic surface and it actually makes the whole thing less dense and buoyant.

And then it will float all by itself.

Absolutely amazing.

All right.

Let's put this thing back in the air 'cause I know that's where it wants to go.

So lift my friends, let it rise.

Excellent.

Solar energy.

It's so fun.

- [Narrator] Have you ever gotten in a closed car on a sunny day and discovered that it was really hot inside?

This is an example of a solar collector.

The windows let the sunlight in and that energy gets absorbed by the dark inside surfaces, the dashboard, floor, steering wheel, and seats.

Those surfaces absorb that light and give off a lot of heat, but the heat can't get out.

Some people use solar collectors to use the sun's energy to heat water for their homes or even heat their homes themselves.

Pretty cool, or should I say warm?

(electrifying music) - So we know the sun gives off a lot of energy and we can appreciate the heat, and the light, And of course the visible light we're aware of.

But Chris, what other kinds of light come off from the sun?

- There are infrared and ultraviolet.

- That's right.

Infrared and ultraviolet.

And we're gonna do a couple of experiments right now to sort of collect evidence of ultraviolet light.

Now because I'm in the studio, I can actually use a special UV light and get the effects that we want.

So here's what we're gonna do.

I've got all these beads here and I sent some of these beads to you guys.

And Adia can you just hold up your bracelet that I sent to you?

Awesome and Adia what happened when you took your bracelet outside?

- It turned into all sorts of colors like, it had yellow and orange.

- Awesome, okay.

So we're actually gonna see that now.

As it is right now all these beads appear white, but when we expose it to ultraviolet light, something amazing happens.

And we start getting some visible color change.

So I'm gonna move this away and you'll see exactly what I mean.

So notice how on this end, we've got some beautiful colors as I move this direction along the table notice it gets lighter and lighter and more white.

And you might be wondering, why is that?

Are those broken?

So here's what I did.

Because this is in plastic, I actually put on sunscreen on top of the plastic.

and I put different levels on.

So I have way down here I've got 15, and then 30 and then 50.

And you'll notice the 50 didn't change very much.

Now, if I go all the way back to this first bag this one has no sunscreen at all.

So it's very, very colorful.

I'm gonna light this up one more time, so you can really appreciate it and I'm gonna explain what happens.

Adia, were you a little surprised when you saw the color changes in your bracelet?

- Yeah.

- So here's something that's really neat.

Normally these beads look white, because they're just reflecting visible light.

And that's because the molecules that make them up are so short, they can't actually absorb any visible light at all.

But something happens in UV, these bent little molecules straighten out.

And when they straighten out, they get longer.

And when they're longer, they're actually long enough to absorb different visible light.

And the longer it is, the different color it is, which is really neat.

So I wanna show you something else too Chris and I know I sent you one of these pieces of paper.

This is a special kind of solar print.

Chris, can you hold yours up?

Tell me what you put on that piece of paper.

- So I put on a lead and left out for three minutes.

- Three minutes, okay.

And did the surface change after three minutes?

- The part that was in the sun changed, got darker.

And the part that was under the leaf stayed the color it was before.

- Okay, now this is a very special kind of paper that responds to UV light.

And I've got several examples here and I put this one out and you'll notice I have this compass on it and this wheel.

And we end up having these really interesting shapes.

I also did a leaf myself, over here.

And then this one, I ended up using a comb, a little badminton birdie, even my tie clip right there.

And this one is my personal favorite, because I have these beautiful leaves.

But the way this works is kind of interesting.

It has a surface chemical on there, which is called Berlin Green.

And when it's exposed to ultraviolet light, it actually has a chemical reaction.

And it turns into something called Prussian Blue.

So anything that was blocked is actually a different chemical than the part that was exposed.

Now, what that means is we're gonna put it in water.

So once we put it in the water, we're able to wash away that Berlin Green, and we're left with two different colors on the surface.

It's amazing.

Ultraviolet light, it's energizing.

Some of the energy that comes from the sun is in a form of light that we can't see, ultraviolet light.

Even though we can't see it, too much ultraviolet light, can hurt our skin and our eyes.

One way to protect your eyes is to wear UV protected sunglasses when it's a bright sunny day.

And to protect your skin, you can apply sunscreen.

Some animals protect themselves too.

Like when elephants throw mud on their skin to protect them from the sun, pretty clever.

- [Narrator] STEM Challenge.

- So have you been having fun learning about solar energy, you guys?

- [Children] Yeah.

- Well I have the perfect STEM challenge for solar energy.

The three of you are going to build solar cars.

So we're gonna use some yeah, a little solar cell powered cars, which is gonna be great.

Your ready to get started?

- [Children] Yeah.

- [Rob] All right, let's do it.

Go ahead.

- [Ian] So once I'm done with this, we can move on to putting the motor onto the wheel.

Dr.

Rob has us making little solar powered cars.

When there's light, the cars will be able to move.

- We have solar panel, a couple plastic wheels, and a motor.

There we go, I got them in.

- The hardest part, was getting the wheels onto the wire.

- [Ian] Maybe we should move the axle.

One of the previous Curious Crew episodes I was on was about torque.

And I think that's one of the problems with my car right now.

Torque is basically the amount of force the motors putting in, but my motor doesn't have enough torque to move the car forwards.

One thing we could do to fix this is by adding gears to make it easier for the motor to move.

- [Callan] Can't get these wires in.

They are being just difficult.

I'm having some technical difficulties because I ended up putting my wires in the wrong spot.

I put the negative wire in the positive spot, and the positive wire in the negative spot.

I think I see what I did wrong.

- I think this is a really great experiment to do because you get to learn about solar energy but also build a tiny car of your own, to race around your house.

- So are you guys ready to show me your solar cars?

- [Children] Yeah.

- All right.

Let's take a look at those, hold them up.

Let's see what they look like.

Those are pretty sharp.

Okay, so you all have solar cells there.

All right, I'm gonna put one of you on the spot.

Ian, can you demonstrate how yours works?

(upbeat music) - [Ian] So here's the car.

- Yep.

Cool, there it goes.

I got nervous I thought it was gonna go right off the table.

Excellent job.

Thanks Ian.

So I was watching you guys work on those and those can be a little tricky, can't they?

But you guys did a great job.

And in fact, I've got one here in the studio too.

And I'm just gonna hold it up just so we can talk about it for a minute.

And you'll see instantaneously when I get that light on it those wheels start turning.

Now the really cool thing about these solar cells is we get that light energy going in, converting it into electrical energy, as it moves through the multilayered silicon there.

And then it goes back to the motor and turns a little gear going against the sprocket attached to that axle, which is really kind of neat.

Now, if you want to start making your own solar cars there's a lot of different devices that you can use, but I will tell you this.

And I think you guys figure this out too.

If I want more power, what might I try?

What do you think Ian?

- Well, you could probably get more solar cells.

- There you go.

Try making your own solar car.

There's a lot of different patterns and kits that are out there, but you can try making your very own yourself too much fun.

- [Narrator] Photovoltaics cells are a great invention that can convert light energy into electricity.

The cell is made of two very thin layers of silicon.

One layer has a bit of phosphorus added to it, the N-type that gives up electrons.

While the other has a bit of Boron, the P-type that attracts electrons.

As light photons enter the N-type side, some of the electrons get free and move to the P-side on a wire, creating a current that can produce power.

The more light that enters the cell, the more energy is produced.

And the best part, there are no mechanical parts that can break down.

(pop music) - So we've seen how solar cells can be pretty effective in making a solar car, but just how much output do they really have?

So I have a whole bunch of solar cells here, you guys.

And I even sent some to you.

Here's what we're gonna do.

We're gonna use a multimeter or a volt meter, hook it up to the solar cell and see what sort of output we have.

You guys go ahead and turn on your lamps.

I'm gonna turn on my lamp and I've got it hooked up to a little solar cell right here.

And I'm curious, what sort of output you guys are getting on yours?

Kah'Reice, what sort of output do you have?

- I'm getting a 1.2 output - Great and Julia, how about you?

- I have 1.1.

- So yours are pretty close, because mine's coming in at 5.4 right now.

That might be a bit of a surprise, 'cause I'm using this teeny tiny little solar cell.

You guys are using these enormous ones.

How can I be getting a bigger output?

Here's something we have to know.

Solar cells are not all the same.

Some are very efficient.

And in fact, this little one that I've got right here is incredibly efficient at transferring that solar energy or in this case light energy, and converting it into electrical energy.

So this makes me wonder though, what would happen if we put more than one cell together?

I wanna show you this I've got right here.

This is an interesting device because it is a series of five solar cells that are actually wired together.

So I'm gonna hook this up, right like this.

And we'll see what sort of an effect we get with this series of panels.

Now, amazingly, I'm only getting about 2.6 or 2.7 and you might be thinking, how is that possible?

There's five of them.

But remember solar cells are not always the same.

This is a very old wired solar cell.

Even though there's five, It's really not that high in output.

But let's think about this.

If we know this original solar cell was really, really good.

What if we were to wire a whole bunch of those together?

I've got a whole series of these wired together.

I'm gonna move the lamp in, get them a little closer together.

My goodness.

I'm already up to 45 volts.

45, that is a lot .

Now keep in mind.

If we wanna power something with solar energy we're going to need a lot of wattage.

We're gonna get this through voltage.

We're gonna get this through current.

Pretty cool you guys.

Solar energy, We're just heating up.

- [Narrator] Have you ever looked at large solar panels?

Each one is made of several silicon solar cells that are connected.

A panel that is 77 inches long and 39 inches wide, has 72 different cells, which produces 350 Watts of power.

Now, if that house has 12 panels, that could produce over 4,000 Watts, wow!

Engineers continue to redesign solar panels, trying to make them more efficient to convert even more light energy from the sun into electrical energy.

Perhaps you'll make the next super solar cell solution.

(scholarly music) - Are you curious about careers in science?

Hi, I'm Janellyn and today, I'm with Marilyn Waite.

Marilyn, tell me, where are you and what do you do?

- I'm in between Oakland, California, and Washington DC.

And I work on sustainable finance and investing.

- What does it mean to invest in climate solutions?

- When we say invest in climate solutions, we mean provide enough money from those who are seeking that return, in businesses and projects that mitigate greenhouse gas emissions.

We have about 30 years to make a change, but if we don't accelerate action in these next 10 years then we will see irreplaceable damage.

So as individuals, we can start using only zero emissions transportation.

That means walking, cycling, taking the train or subway and using electric vehicles.

- What is your advice to kids who are interested in a career like yours?

- My advice is to develop a curiosity for how the world works.

Read, watch, and listen to learn about finance and investment.

- Marilyn Waite got me really invested in how I can help with climate change.

Explore your possibilities.

(scholarly music) And now back to Curious Crew.

(upbeat music) (hip hop music) - Well Callan and Ian saw how darker colors absorb more heat, making the temperature go up.

- Are you thinking the darker sides of the blade are heating up?

- It's possible, but if the darker side absorbs more heat, I still don't get why it would move.

- Well remember that the black paper heated up the area around it too.

Maybe the air particles get some of that energy, just like the balloon.

- If that were true, it would bounce around with greater energy.

Maybe it hits something harder, causing it to swing.

- That makes sense.

Both the radiometer and the grasshopper need their light to move, but the grasshopper uses the solar cell to convert light into electrical energy.

(funk music) - So have you guys had fun learning about solar energy today?

- [Children] Yeah.

- Awesome, well, we're back to these discrepant events and of course these delightful grasshoppers, that are just bouncing around.

You gotta love that.

So I know three of you have been working really hard to try to explain these phenomena.

And Adia, let's start with you.

Let's talk about the grasshoppers.

What have you guys figured out?

- We figured out that, when the light hits the grasshoppers it's what causes them to jump.

- That's exactly right.

Because we actually have a little solar cell, that's on the back, and it can convert that solar energy into electrical energy.

The energy comes into the solar cell.

It actually releases some electrons from the upper silicon level and it moves down a little current towards a motor that causes it to wiggle.

And in fact, we can even adjust the legs on the grasshopper, which will make it dance and wiggle in a different way.

Which is too much fun.

I gotta see it one more time.

It's just delightful.

I love it.

This one wants to play too, there you go.

Okay, so how about the radiometer here?

Kah'Reice, what have you guys figured out about that?

- We think the light photon can enter the glass and heat up the black side of the blade, and the area around it.

- Excellent okay.

So we know that the darker side is actually gonna be absorbing more of that energy.

And that impacts the air particles that are around there.

Okay we know it's a closed system too.

So there's no wind involved here at all.

So how can that light energy actually get that to spin Julia?

- Some of the energy from the darker side of the blades will transfer to the air particles.

If they have more energy, it will bounce off the darker side of the blades more often and with more energy, getting it to spin.

- Excellent okay, so those particles are just hitting the darker side more often and with more energy.

And so it just constantly gets pushed away.

Poor Sir William Crookes, He did not understand how this worked, but you guys figured it out well done.

The other trick to this that really makes it work well is that the globe actually has a partial vacuum.

And so there's even fewer air particles inside.

Which reduces the air resistance quite a lot.

And in fact, the rotor that's there is nearly frictionless.

So when we put this in light, whether it's going to be from my lamp or whether we put it on a window sill and get the sun's energy, we can have this thing spinning.

And it's a great decoration and a wonderful toy obviously, to mesmerize your friends.

Too much fun.

So remember my friends, - [Children] Stay curious.

- And keep experimenting.

- [Narrator] Get your curiosity guide and see more programs at wkar.org - [Narrator] Support for Curious Crew is provided by MSU Federal Credit Union.

Offering a variety of accounts for children and teens of all ages, while teaching lifelong saving habits.

More information is available @ msufcu.org.

Also by the Consumer's Energy Foundation dedicated to ensuring Michigan residents have access to world-class educational resources.

More information is available at consumers energy.com/foundation Consumer's Energy Foundation, supporting education and building sustainable communities in Michigan's hometowns.

And by viewers like you, thank you.

- Keep smiling guys, keep smiling.

Washes away that Prussian, sorry I did it again sorry.

(laughing) Yeah.

(upbeat music) (gentle music)