Video transcript of Episode 10: Vanishing Coin

Below is the full transcript of Episode 10: Vanishing Coin delivered by IOP's Dr Taj Bhutta.


Transcript

On-screen text reads: “On-screen text reads: "Do Try This at Home from the Institute of Physics. Episode 10: Vanishing Coin."

Camera cuts to a close-up shot of a see-through drinking glass sitting on top of a ramekin.  There is a coin underneath the glass. Some background music plays.

Saf (voice-over): "Now you see it..."

We see someone pour some water in the glass.

Saf: (voice-over): "Now you don’t!"

We see the coin disappear as water is poured in. Camera cuts to a glass filled with water. A jam jar lid has been placed on top of the coin and there is no sign of the coin.

The music stops playing, and we hear a whooshing noise. The screen swipes right and the camera cuts to Taj who is seated in his living room.

Taj: "Hello and welcome to another episode of Do Try This at Home brought to you by the Institute of Physics.

"We’re making these videos for parents and carers across the UK and Ireland so that you can explore science together at home with your kids.

"My name is Taj and I’ve got another optical illusion for you. This one’s called Vanishing Coin. I’m going to hand you over to my niece to explain what we need to do."

Camera cuts to a medium shot of Saf. She is seated at a kitchen table.

Saf: "So what you’re going to need is a tall drinks glass with straight edges, some water, a jug, a tea towel, a small jar or dish with a dip to put your coin on."

Camera cuts to a close-up of the table. As she’s speaking, she points to a see-through drinking glass, a glass milk bottle which has been filled with water, a drinks jug, a tea towel, and a see-through dessert ramekin. The ramekin has a dip in the bottom of it.

Saf: "Check there’s enough space for the coin by putting the glass on top."

Saf places the ramekin upside down and places the coin on top. She places the glass on top of the ramekin. As the camera points down at the glass, we see that while there is a gap of air between the coin and the glass, the coin is still visible.

Saf: "Then, for the top of the glass, make a lid or have a look around the house for something that will fit."

We hear a popping noise, and a circular cardboard lid appears on top of the glass. We hear further popping noises as different options are tried out as lids. We see a toy gorilla, a Terry Pratchett book, a square biscuit tin lid, a tagine lid, a larger plate, and then a smaller jam jar lid. The last lid fits so we hear a bell and see a tick mark next to it.

Camera cuts back to Saf. The drinking glass has been set aside. Saf removes the coin from the top of the ramekin and hides it.

Saf: "Now fill up your glass with water."

Saf pours the water from the bottle into the glass until it almost reaches the top.

Saf: "This is how much you’ re going to need. Pour this into the jug. Use a tea towel to dry everything off."

Saf pours the water from the glass into the jug, and then uses a tea towel to mop up the spills.

Camera cuts to a close-up of Saf drying the inside of the glass. We hear a clunking sound as she sets the glass down.

Camera cuts to a medium shot of Saf. The tea towel has disappeared but jug of water, the ramekin, the drinking glass, and the empty milk bottle are still on the table.

Saf: "And you’ re all set up. All you need to do is call in your family member.

"Norah!"

We hear some music playing as Norah walks in.

Saf: "Have you got a coin I can borrow?"

Norah walks away to find a coin and comes back. Camera cuts to a close-up shot of her placing the coin on the upside-down ramekin. We hear a clinking noise as she sets the coin down.

Saf: "Don’t worry, it won’t go anywhere."

Camera cuts to Norah, who watches Saf place the drinking glass on top of the ramekin.

Saf: "Now you see it…"

Camera cuts to a close-up shot of water being poured into the glass. The jam jar lid is placed on of the glass. The coin has disappeared.

Saf: "Now you don’t!"

Camera cuts to Norah who is looking intently at the glass. Saf pulls the jug away. Norah looks closely to see if she can spot the coin under the glass. She can’t. She looks at the camera and pulls a face. We hear a low-pitched grumble.

Camera cuts back to Taj. He also has a glass of water sitting on the table in from of him. The glass is sitting on a ramekin and is covered by a lid.

Taj: "Don’t worry Norah, we’ll find it for you. So, what’s going on here and how do you explain it to your family?

"Let’s take the lid off this one and see what Saf wasn’t showing Norah – a reflection of the coin."

Taj removes the lid from the glass, and we see a reflection of the coin sitting underneath the glass.

Taj: "And that’s a clue, but there’s quite a few bits to this one so let’s break it down."

Camera cuts to a close-up shot of the glass. Taj picks the glass up off the ramekin.

We hear a whooshing noise. Camera cuts a line drawing featuring the ramekin with the coin on top. The ramekin is in the centre of the screen.

Taj (voice-over): "At the start Norah can see the coin because light bounces off it in all directions and some of it travels in a straight line to our eye. Saf can see it because some of it travels in a straight line to her eye."

The name ‘Norah’ appears at the top right and the word ‘Saf’ at the top left. Two thick straight lines appear. The starting point for each line is the top of the coin. One of the lines heads off in the direction of ‘Saf’ and the other line heads off towards the word ‘Norah’.

Taj: (voice-over): "When Saf puts the glass down some of the light reflects but most of it still makes it through."

The lines disappear. A glass is placed on top of the ramekin. We hear a clinking sound as it is placed down.

The camera zooms in to the top right corner of the ramekin. A thick line appears which comes from the coin but this time it travels through the bottom of the glass. The line is travelling upwards at an angle until it hits the inner wall of the glass. The line then splits in two: a thick line continues in the same direction through and beyond the glass, whilst a thin line bounces off the side and heads off in the opposite direction.

Taj (voice-over): "For this trick to work, Saf needs to make all the light reflect. That’s what adding the water does. It completes a five-layer structure in which the conditions are just right for all the light to reflect. Light travelling upwards gets trapped, can no longer reach Norah and so the coin seems to vanish. The light can still get out the top, but Saf had that covered."

An animation shows the glass being filled and we hear the sound of water pouring into a glass.

We hear 5 popping noises. At the same time 5 words appear: ‘air’, ‘glass’, ‘water’, ‘glass’, and ‘air’.  Each word represents a layer through which the light from the coin must pass. The light bouncing from the coin now has to travel through the air, the bottom of the glass, the water, the side of the glass and – finally – though the air to Norah and Saf.

A line appears from the coin. We see the line change direction as it moves from one material to another. It travels to the bottom of the glass, bends upwards a little whilst travelling through the glass, and then heads towards the inside of the glass. The water in the glass causes the angle of the line to change again so that it reflects off the side of the glass and bounces back inside the glass.

We hear a whooshing noise. The camera zooms out so we can see the more of the glass. The line has bounced off the wall of the glass and crosses over another line coming in the opposite direction. Both lines make it to the top of the glass, but a lid prevents their escape. We hear a clinking sound as the lid is dropped on top of the glass.

Camera cuts to a medium shot of Taj.

Taj: "Don’t worry if you don’t totally get the science. Enjoy the trick or head over to our website for more information.

"Well, that’s all for this time, so it’s goodbye from them and it’s goodbye from... me!"

The image is replaced by some on-screen text which reads: "Do Try This at Home from the Institute of Physics. For instructions and more Do Try This at Home films visit iop.org/athome. These experiments have not been specifically safety tested for home use, but we believe them to be safe if the instructions are followed. Adult supervision is recommended as appropriate. All experiments are carried out at your own risk."