Units and SI equivalents
Prefixes |
|||
| symbol | prefix | base 10 | English name |
| E | exa- | 1018 | one quintillion |
| P | peta- | 1015 | one quadrillion |
| T | tera- | 1012 | one trillion |
| G | giga- | 109 | one billion |
| M | mega- | 106 | one million |
| k | kilo- | 103 | one thousand |
| h | hecto- | 102 | one hundred |
| da | deca- | 101 | ten |
| d | deci- | 10-1 | one tenth |
| c | centi- | 102 | one hundreth |
| m | milli- | 103 | one thousandth |
| μ | micro- | 106 | one millionth |
| n | nano- | 109 | one billionth |
| p | pico- | 1012 | one trillionth |
Units of radioactivity
| Bq | becquerel | A becquerel is one decay (often referred to as a transformation) per second. This decay is normally expressed as much larger amounts, such as terabecquerels (tBq) or gigabecquerel (GBq). | |
The SI system of units
The three basic units are:
- metre (m)
- kilogram (kg)
- second (s)
The SI unit for force is the Newton (N). It is defined as the force that will accelerate a mass of one kilogram (kg) at a rate of one metre per second.
Force (N) = mass (kg) x acceleration (m s-2)
A force can only move an object because that force has energy. The SI unit of energy is the joule (J)
The amount of energy used to move an object can be calculated by the following equation:
Energy (joules) = Force (newtons) x Distance (metres)
Power is the rate at which energy is converted from one form to another or transfrered from one place to another. The unit of power is the watt (W).
One watt is defined as the conversion, or transfer, of one joule per second.
The usage of energy over one hour of time is defined as a kilowatt-hour (kWh).
A kilowatt is 1000 watts per second. Since there are 3600 seconds in an hour:
one kilowatt-hour (kWh) = 3.6 x 106 Joules which can be better experessed as 3.6 MJ (note from the table above that a mega Joule (MJ) is a million Joules).
Current, voltage, resistance, power and energy
The ampere is the unit of elecric current.
The voltage of an electricity supply is defined as the difference in electrical potential between two points. A single volt is defined as one amp flowing for one second from a one volt supply such that the energy supplied is exactly one joule.
Ohms Law defines resistance as the voltage (V) across a component divided by a current (I) flowing through the component: R = V + I