Units Prefixes AIM To learn the basic units

Units & Prefixes AIM: To learn the basic units used in electronics and to understand how prefixes and standard form can be used to make large and small numbers easier to work with. PRIOR KNOWLEDGE: Basic maths – powers of 10, standard form www. pfnicholls. com

Quantities & Units The standard quantities and their associated units are: • Current (I) measured in amperes (A) E. g. A kettle takes a current of 12 A • Voltage (V) measured in volts (V) E. g. We use a 9 V battery • Resistance (R) measured in ohms (Ω) E. g. An LED needs a 470 Ω series resistor

Quantities & Units The standard quantities and their associated units are: • Energy (E) measured in joules (J) E. g. In 10 minutes the bulb dissipates 1000 J on energy • Power (P) measured in watts (W) E. g. Using 100 J per second is a power of 100 W • Charge (Q) measured in coulombs (C) E. g. In 5 minutes a charge of 20 C flows through the bulb

Quantities & Units The standard quantities and their associated units are: • Time (t) measured in seconds (s) E. g. The circuit remained on for 20 s • Frequency (f) measured in hertz (Hz) E. g. The astable circuit had a frequency of 25 Hz • Capacitance (C) measured in farads (F) E. g. The circuit needed a 0. 01 F capacitor

Prefixes for small quantities Prefix Milli Symbol m Prefix meaning 1000 Standard form 10 -3 m A current of 5 m. A in standard units is 5 1000 = 0. 005 A A power of 200 m. W in standard units is 200 1000 = 0. 2 W A voltage of 0. 04 V in more convenient units is 0. 04 1000 = 40 m. V

Prefixes for small quantities Prefix Micro Symbol Prefix meaning 1000, 000 Standard form 10 -6 A current of 5 A in standard units is 5 1000, 000 = 0. 000005 A A power of 2000 W in standard units is 2000 1000, 000 = 0. 002 W which is is also 2 m. W because 1000 W = 1 m. W Capacitance of 100 F in standard units is 1000, 000 = 0. 0001 F In the above examples, 5 A is more conveniently written as 5 10 -6 A and 100 F as 100 10 -6 F

Prefixes for small quantities Prefix Nano Symbol n Prefix meaning 1000, 000 Standard form 10 -9 n A current of 5 n. A is 5 1000, 000 = 0. 00005 A which is really inconvenient to write down so it should always be written as 5 10 -9 A Power of 2000 n. W in standard units is 2000 1000, 000 = 0. 000002 W which is is also 2 W because 1000 n. W = 1 W Capacitance of 47 n. F in standard units is 47 1000, 000 = 0. 000000047 F which is too inconvenient so it should always be written as 47 10 -9 F

Prefixes for small quantities Prefix Pico Symbol p Prefix meaning 1000, 000 Standard form 10 -12 p Pico is a really small quantity and is really only used for capacitance A capacitance of 33 p. F in standard units is 33 1000, 000 = 0. 0000033 F which is too inconvenient. It should always be written as 33 10 -12 F 56 n. F = 56, 000 p. F because 1 n. F = 1000 p. F 470 p. F = 0. 47 n. F because 1 p. F = 0. 001 n. F

Prefixes for large quantities Prefix Kilo Symbol k Prefix meaning 1000 Standard form 103 k A current of 5 k. A in standard units is 5 1000 = 5000 A A resistance of 68 kΩ in standard units is 68 1000 = 68, 000 Ω A voltage of 2400 V in more convenient units is 2400 1000 = 2. 4 k. V

Prefixes for large quantities Prefix Mega Symbol M Prefix meaning 1000, 000 Standard form 106 M A current of 5 MA in standard units is 5 1000, 000 = 5000, 000 A A resistance of 1. 2 MΩ is 1. 2 1000, 000 = 1, 200, 000 Ω A power of 6, 000 W in more convenient units is 6 MW

Prefixes for large quantities Prefix Giga Symbol G Prefix meaning 1000, 000 Standard form 109 G A frequency of 2. 4 GHz in standard units is 2. 4 1000, 000 = 2400, 000 Hz. This is not a convenient number to write out so it would be written as 2. 4 109 Hz A resistance of 0. 2 GΩ is written as 200 MΩ because 1 GΩ = 1000 MΩ

Prefixes for large quantities Prefix Tera Symbol T Prefix meaning 1000, 000 Standard form 1012 T Tera is a very large prefix and is really only applied to very high frequencies (THz) or large amounts of bytes of data (TB) in hard drives in computer systems A frequency of 4 THz in standard units is 4 1000, 000 = 4000, 000 Hz. This is not a convenient number to write out so it would be written as 4 1012 Hz

Summary Quantities and Units

Summary Working with small numbers

Summary Working with large numbers

Questions 1. What is 7 m. A in standard units of amperes? 2. What is 0. 00004 V in a more convenient form? 3. What is 56 J in standard form? 4. What is 47 F in standard form? Or in standard units? 5. What is 27 n. F in F? 6. What is 0. 1 F in n. F? 7. What is 5 ms in standard form and in standard units of seconds? 8. What is 0. 2 s in ms?

Answers 1. 7 m. A = 0. 007 A (divide by 1000) 2. 0. 00004 V = 0. 04 m. V or 40 x 10 -6 V or 4 x 10 -5 V 3. 56 J = 56 x 10 -6 J 4. 47 F = 47 x 10 -6 F or 0. 000047 F 5. 27 n. F = 0. 027 F (divide by 1000) 6. 0. 1 F = 100 n. F (multiply by 1000) 7. 5 ms = 5 x 10 -3 s or 0. 005 s 8. 0. 2 s = 200 ms (multiply by 1000)