Hold up one hand. How far can you count on 4 fingers? If each finger is a binary digit you can count to more than 4. By the end of the lesson you will know how far you can count in binary on 2 hands (more than one thousand!)
Put cards in numeric order, zeroes up, smallest value on right. This is zero.
Turn cards over in combination to make a series of numbers in range 0-15. Is there a pattern to the way the cards are turned over?
Make a series of further numbers in range 16-127.
What type of number does each card represent?
What is the biggest number that can be made in 2 cards? 3 cards? etc.
Complete the expression: the biggest number in n cards is: ...
How many numbers do 2 cards represent? 3 cards? 4 cards? etc.
How many cards do you need for 255?
How many numbers can you represent with 10 cards? How is this number used when talking about computers?
Recap: How far can you count on one hand?
What name is given to 2^20? 2^30?
Turn the cards face down again. Put binary numbers on board (pupils can do this). Given a binary number what is its decimal value? Try this in your head then use the cards to check if you are right.
Use digits on hands to show binary numbers and get the answers in denary. What is the largest number you can show on one hand? On two hands? On two hands and two feet?
Extension
What happens to binary numbers when you insert a zero on the right? Or delete the left-most card?
The ASCII and Unicode values for common codes are as follows:
0 (zero) : 48
Subsequent ASCII codes are 49, 50, 51, 52, 53, 54, 55, 56, 57
A : 65
Subsequent letter codes are 66, 67, etc. Lower case 'a' is 97, others follow on in sequence.
Translate a short message into character codes and pass it to a neighbour to decode. Find a list of codes by searching Google for 'ASCII character codes'. Send the messages by email.
Extension
Your message is encoded but not encrypted. What is the difference between these two words? Can you use a simple strategy to encrypt your message? Compose a different message in code values, encrypt it with a simple method and then pass it to your neighbour to decode. How will they set about decoding it? Hints here.
Useful program here. You can use this to encrypt your emails!
Cryptography is an enormous and complicated field and a significant branch of mathematics.