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Chapter 11 Electrical Engineering 227
Use the following formula:
R = E / I
= 3 V/0.1 A
= 30 Ω of resistance
For example, let’s say you want to calculate
the resistance of a fl ashlight bulb. You know that
your batteries are providing 3 V and you are
drawing 0.1 A (or 100 milliamps) of current fl ow.
Math
Scientific Notation
It is very common to encounter extremely large and small numbers when working with or studying elec-
tricity and electronics. Sometimes numbers are too large or small to be conveniently written. They can be
represented using scientific notation. The base number in scientific notation is a number from 1 to 9 and is
multiplied by a power of ten.
For example, 7 × 103 (seven times ten to the third power) is 7 × 10 × 10 × 10 = 7,000. The 3 is an expo-
nent. Exponents show how many times to use the number in multiplication. Positive exponents are used for
numbers larger than the base number, and negative exponents are used for numbers that are smaller than
the base number.
For example, imagine you want to represent five megawatts using scientific notation. The metric
prefix mega- refers to million. Therefore, you are trying to show 5,000,000 watts. That can be shown as
5 × 10 × 10 × 10 × 10 × 10 × 10. Using scientific notation, it is 5 × 106 watts.
The metric prefix milli- is used to show thousandths of a base number. For example, seven milliamperes is
seven thousandths of one ampere, or 0.007 amperes. Using scientific notation, this is shown as 7 × 10–3. The
exponent is –3 because the decimal place moves to the right three places from 7 to 0.007.
Figure A shows common metric prefixes and their symbols, decimal value, and value in scientific notation.
Write the following numbers using scientific notation, converting units where necessary.
1. 8,730,000,000 watts
2. 6,270 nanovolts
3. 0.00047 amperes
4. 4,383,000 ohms
5. 2,000 volts
6. 3.2 kilohms
Prefi x Symbol Value Decimal
giga- G 109 1,000,000,000
mega- M 106 1,000,000
kilo- k 103 1,000
milli- m 10–3 0.01
micro- μ 10–6 0.000001
nano- n 10–9 0.000000001
pico- p 10–12 0.000000000001
Figure A.
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