# CIE IGCSE Biology: 复习笔记：2.1.4 Converting Between Units: Extended

### Converting Between Units: Extended

#### Using millimetres and micrometres as units

• The table below shows how millimetres are related to two other measures of length
• What this basically means is that 1mm = 1000µm and 1cm = 10,000µm
• This usually comes up in questions where you have two different units and you need to ensure that you convert them both into the same unit before proceeding with the calculation
• For example:

Example extended magnification question

• Remember 1mm = 1000µm
• 2000 / 1000 = 2 so the actual thickness of the leaf is 2mm and the drawing thickness is 50mm
• Magnification = image size / actual size = 50 / 2 = 25
• So the magnification is x 25 (NO UNITS)

#### Exam Tip

If you are given a question with two different units in it, make sure you convert them to the same unit before doing your calculation.If you don’t, there is a good chance that your answer will be the same as one of the incorrect options in a multiple choice question so you may think you got it right when, in fact, you haven’t!The following diagram may help with unit conversion between mm and µm: