AMASE: How Does the Light in the Fridge Work?

Posted on Thursday, May 14th, 2020


[Female child opening the fridge door, closing it, opening it again, woman enters frame]

Joanne: Ahh, Mara, whatcha doin? Are you trying to attract penguins again? 

Mara: No I’m trying to figure out how the light goes out when I close the door. Can you help me? I'm gonna go inside.

[Mara opens door and motions to get into the fridge.]

Joanne: No. Get, get. No that's not a good idea and I already know the answer.

Mara: How?! 

Joanne: Electricity.

Mara: What? 

Joanne: Right. Okay so you see this thing right here in the door. When the door closes it presses on it. This is called a switch.

[Joanne bends down and presses the switch with the fridge door open turning the light off and on.]

Joanne: When you press on it…

Mara: The light goes out.

Joanne: Yeah, the light goes out!

Mara: It’s like the switch in my bedroom. When it’s bed time you turn it out.

Joanne: Exactly! It's a switch and a light. And that's a very simple circuit. So let's get your circuit kit out and we'll build it and we'll see what parts we need. 

Mara: Okay! 

[Video cut from fridge to Joanne and Mara sitting at the kitchen bar.]

Joanne: So, a lightbulb is a device that's designed to turn electrical energy into light and heat. There's a small thin wire inside a glass bulb. 

Mara: Okay so here's a mini light bulb. I'm gonna put this into the circuit here and see what happens. Nothing happens! What?! 

Joanne: You're missing a key ingredient. What do you need in your flashlight in order for it to work when you flip the switch? 

Mara: Uhm… batteries! 

Joanne: Batteries! Alright so let's add in some batteries and a switch and we'll see what happens with our simple circuit. Alright you've got a light bulb, some batteries and a switch in a closed circuit. Let's flip the switch. 

Both: Yay! 

Mara: It works!

Joanne: Alright so in order for the light bulb to light up you need batteries to be the source of energy and you need a closed loop for the electricity to flow around.

Mara: Okay so if I take this piece out it doesn't work anymore.

Joanne: Exactly. It's like a missing piece of train track. 

[Video cuts to footage of a train tracks]

The train needs a complete loop in order for it to travel around. It's the same for the electricity.

[Video cuts back to kitchen bar.]

Joanne:  The switch is basically opening and closing the train track.

Mara: Oh I guess I know how this works now to you too. 

[Mara presses the tweezers into the side on a game of Operation. Buzzing sound.]

Joanne: Yup! So you're closing the train track. 

[Joanne uses tweezers to demonstrate. Buzzing sound.]

The metal wires touch the metal at the side of the opening, closes the train track the electricity can flow through the nose as long as you have batteries. 

Mara: Okay, but where are the batteries for the fridge?

Joanne: Aha. So, the fridge is a little bit more complicated than our flashlights. So, we
don't use batteries for the fridge we use energy from the wires outside the house. The wires are connected to wires in the walls which distribute the energy all through the house to things like the fridge, the stove, the lights, the air conditioning and all those things. 

Mara: Okay, but where does the energy come from so it can go through the wires and into our house?

Joanne: Also a good question! It comes from the generating station which creates electricity from all kinds of different energy sources. So it might be wind, it might be sunshine, it might be waterfalls. 

[Video cut to a dam.]

Mara: Are you 100% sure that the light goes out when we shut the fridge door?

Joanne: I am 100% sure because that's how electricity works. Would you like me to prove it to you?

Mara: Yes 

Joanne: Alright. Sign off Horace. 

Mara: Thanks to Jonathan and Carter, grade 3 students in Fergus, Ontario, for the idea for this video and thanks for watching ask me anything science edition. 

Joanne: Alright let's see what happens...

[Video cut to fridge door opening. Sign in fridge says Science Is Cool. Door closes, light goes out.]


Today 3M National Teaching Fellowship recipient Dr. Joanne O'Meara and junior scientist Mara answer a question from some students at JD Hogarth Public School who want to know the answer to one of the oldest questions in science... how do you know the light in the fridge goes out when you close the door?!

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