# An introduction to NOT gates

A NOT gate has only one input. It's job is to 'invert' the input. In other words, if the input signal is a 1, then it outputs a 0. If the input signal is a 0, it outputs a 1. If the output was a light, then you would turn the light on by having the switch off! When you turned the switch on, it would switch the light off. The truth table for this logic gate is as follows:

A |
B |

0 | 1 |

1 | 0 |

**Q1.** How many inputs has a single NOT gate got? How many outputs are there?**Q2.** How many permutations of inputs are there to a NOT gate? How did you work it out using powers of 2?**Q3.** Study this diagram:

How many NOT gates have been used?**Q4.** Complete the truth table below. Work out column B first using column A. Then work out column C using column B.

A |
B |
C |

0 | 1 | |

1 |

**Q5.** Study this diagram:

How many inputs are there? How many permutations of inputs are there? How did you work out the number of permutations?**Q6.** Complete the truth table below.

A |
B |
C |
D |

0 | 0 | ||

0 | 0 | ||

1 | 0 | ||

1 |

**Q7.** An AND gate followed by a NOT gate is a very important kind of logic gate. It gives you the exact opposite of the output from an AND gate. It's so important that it actually has it's own symbol and name. Here is the original diagram of an AND gate followed by a NOT gate:

and here is the equivalent combined symbol:

What is the name of this new symbol? Use the Internet to find out.**Q8.** Study this diagram:

How many inputs are there? How many permutations of inputs are there? How did you work out the number of permutations?**Q9.** Complete the truth table below.

A |
B |
C |
D |

0 | 0 | ||

0 | 1 | ||

1 | 0 | ||

1 | 0 |

**Q10.** An OR gate followed by a NOT gate is a very important kind of logic gate. It gives you the exact opposite of the output from an OR gate. It's so important that it actually has it's own symbol and name. Here is the original diagram of an OR gate followed by a NOT gate:

and here is the equivalent combined symbol:

What is the name of this new symbol? Use the Internet to find out.