# The LED Torch - Resistors and Ohm's Law

## 1 Colour Codes

### Learn It

- Resistance is measured in Ω
- You know that the narrower the wire through which electricity passes, the more the resistance it has.
- The most common type of resistors called
*Carbon Film*resistors are made up of a carbon tube into which a grooves have been cut. - The grooves mean there is less carbon for the current to pass through, so the resistance can be increased by having a deeper groove.

### Learn It

- Resistors are colour coded so we can tell what there resistance is.
- Most resistors have 4 bands painted on the outside.

- Starting at the opposite end to the Gold or Silver band (In this image that would be the right hand side):
- The first band gives us the first number
- The second band give us the second number
- The third band gives us the number of zeros.
- The fourth bands gives us the tolerance.

Colour | 1st Band | 2nd Band | 3rd Band (Multiplier) | Tolerance |
---|---|---|---|---|

Black | 0 | 0 | 0 | |

Brown | 1 | 1 | 1 | |

Red | 2 | 2 | 2 | |

Orange | 3 | 3 | 3 | |

Yellow | 4 | 4 | 4 | |

Green | 5 | 5 | 5 | |

Blue | 6 | 6 | 6 | |

Violet | 7 | 7 | 7 | |

Gray | 8 | 8 | 8 | |

White | 9 | 9 | 9 | |

Gold | 5% | |||

Silver | 10% |

- So for example, the resistor pictured above has the colours:
- Brown - 1 (First number is 1)
- Black - 0 (Second number is 0)
- Yellow -4 (4 zeros)
- Gold - +/-5%

- This means it is a 100000Ω resistor, or what we would normally call a 100kΩ resistor.
- The 5% tolerance means that the actual resistance can vary by + or = 5%, which in this case would be 0.05 X 100000 = 5000Ω

## 2 Assessment

### Badge It - Silver

#### Progress ladder **Red**, Identify several electronic components, with assistance.

- Look at the resistors in this photograph. You can magnify them by hovering with your mouse cursor.

- For each resistor, use the colour table to identify it's resistance.

## 3 Ohm's Law

- You've seen how increasing the resistance in a wire can effect the current passing through the wire.
- It is therefore possible to reduce the amount of current flowing in a circuit, by adding in resistors.
- To do this we use
`Ohm's Law`

`V`

is for Voltage,`I`

for current and`R`

is for resistance.- We can rearange the equation to make
`I`

the subject, which will allow us to calculate the current in a circuit. - Look at the animation below to see how.

- So there are three different ways of writing Ohm's Law

## 4 Assessment

### Badge It - Gold

#### Progress ladder **Orange**, Identify several electronic components, without assistance.

- Copy this table shown below

Voltage(V) / V | Current(I) / A | Resistance(R) / Ω |
---|---|---|

- Look at the simple circuit detailed below.

- Hit the button to generate a new question. Fill in the provided values into your copy of the table and then caluclate the third value for yourself.
- Sometimes the current is described in
`mA`

. This is short for milliamps, which are a thousandth of an amp. (Just divide it by 1000 to calculate the current in amps)