# CS Unplugged – Binary digits (sample classroom lesson)

Today we are going to learn about Binary Digits.
Hands up if you’ve heard of a thing called
a bit in a computer. Have you heard of a bit? A bit comes from binary digits. We take the first letter of binary and add the last bit of digit and we shorten it to bits. Right now we’ve got five bits standing up
here. Let’s see what that means. I’m going to give you the number 1, you’re
going to be a bit that represents 1 dot. You’re going to be a bit that represents 2
dots. What’s the next number? Call it out. (4, 3) Hands up if you think 3. That’s our counting system. Let’s see if you are right with binary. Oh! It’s 4. What could be the next number? Yes? (6 or 5).
It could be 6 or 5. It’s actually 8. What’s happening with those numbers? What’s the next number Oliver? (16) Is he right? What’s the next number after 16 then? Jacob (32) Oh, what comes after 32? (136) Could be, what else could it be? Lachlin (64) Is he right? (yes). What’s the next number that comes after 64? Thomas (128) After that? Jacob? (256) There we go. Does anyone know what the next one is? Ben. (512) So when we… What’s the next one Jacob? So with only a few bits we can count up really
high, right? If we look at this we can count 1, 2, 4, 8,
16 dots. Let’s look at what that means inside a computer. A bit can be on or it can be off. So this bit can be on or it can be off. Now what I want you guys to do is think of a number between 31 and 1. Hands up if you thought of a number. Ben, what number (12). 12 What we want to do is look at these dots and show 12 dots in binary. Do we want 16 on or off? (off). Turn off please. If we are making the number 12 do we want 8 on or off? (on) OK, how many’s left over then? (4) Do we want 4 dots on or off? (on). What about 2? (off) Why? Why is 2 getting turned off? (Because You’ve already made 12 with the 8 and 4). So 1 stays on or …? (off) Who can tell me in binary what 12 would be, representing 12? Who wants to have a go? (off, on, on, off, off) Thumbs up if you agree. What about Elarn, do you want to make, can you guys all turn yourselves back on again, Elarn, choose a number that we are going to make. (24) 24 Can you just turn yourself back on please. For 24 do we want 16 on or off? (on) 8 on
or off (on) 4, (off) 2 (off) 1 (off). Elarn, what is binary for 24 dots? (on, on,
off, off, off). Could we make the number 1 for me. How would we do that? How would we make the number 1? (black, black, black, black, white) Can you guys make that? Now that you’ve seen the number 1 is there
another number you can think of that would be even lower than 1? Will? (0) How would you make 0? (turn off the white one). We can make the lowest number zero and the
highest number, if you turn on all your cards back on, with five bits, what’s the highest
number we can represent? Ben? (31) Hands up if you agree with Ben? It is 31. If we can make 31 what’s the next card going to be? If I join this and become the sixth bit what’s
the next number? (32) 32. If I turn on 32 these guys all have to turn (off)
off to make 32. If you guys all turn off. Let’s do some counting and see what happens
with the different bits. We’ve got zero. What do we need to do to make 1? Yes, give the instructions (turn on 1). 2, how do we make 2? Tell the people (turn off 1, turn on 2) 3? Lachlin, go (turn 1 on and keep 2 on). 4? (turn 2 and 1 off and turn 4 on) 5? (turn 1 on…)
What are you noticing about the first bit? Zander, what are you noticing (it does
all the work) It seems to be doing all the work. Why does it seem that it is doing all the
work? Ben? (you can’t make odd numbers without it) Turn on all your bits again. What’s the difference between the first bit
and all the other bits that you can see? William? (number 1 is the only odd number) It’s the only odd number. We can represent lots of numbers right? I wonder how we would represent letters? Turn to the person next to you and come up
with any ideas you might have about how to represent letters. How do you think you might represent a letter? 5, 4, 3, 2, 1, eyes this way. Hands up whose got a suggestion as to how
we can use these to represent letters. What ideas have you got? (You could have the number represent the letter. 26 could be Z and A could be 1) 26 could be Z, A could be 1, what would B be then? Jacob? (2), what would C be (3), What would D be? (4), E? (5). I think you’ve got the hang of it. I wonder if you can work out what I’m sending
you. I’m going to send you a message. Black, white, black, black, black. What number is that? (8). What’s the eighth letter in the alphabet? (H). Hold that in your head. Off, on, off, off, on. What number’s that? (9) What have I said to you Zander? (The word that you said to us is “Hi”) Is it? Do you agree with him? Did we do “Hi”? But these are just dots and cards that are
on and off, can I really communicate a message to you doing that? (yes) Let’s see how good you are. Let’s see if I can communicate what month
I was born in. Are you ready? Off, on, on, off, off. What month was I born in? Whisper it to me, so many people know the answer,
go. (December) You’re right. So using binary digits and using these dots
we can communicate anything from a letter to a number. You can even do images, you can do sound,
you can do movies. Everything involves bits because inside a
computer isn’t a whole lot of cards like this, isn’t a whole lot of zeros and ones, but it’s
a whole lot of things that need to be turned on or turned off.