3. Algebra and Exponents

Lesson

Scientific notation or standard form is a compact way of writing very big or very small numbers. As the name suggests, scientific notation is frequently used in science. For example:

- The sun has a mass of approximately $1.988\times10^{30}$1.988×1030kg which is much easier to write than $1988000000000000000000000000000$1988000000000000000000000000000kg
- The mass of at atom of Uranium (one of the heaviest elements) is only approximately $3.95\times10^{-22}$3.95×10−22g. That is $0.000000000000000000000395$0.000000000000000000000395g.

Remember

In scientific notation, numbers are written in the form $a\times10^b$`a`×10`b`, where $a$`a` is a number **between** $1$1 and $10$10 and $b$`b` is an integer (positive or negative).

- A negative exponent indicates how many factors of ten
**smaller**than $a$`a`the value is. - A positive exponent indicates how many factors of ten
**larger**than $a$`a`the value is. - A exponent of zero indicates that the value is $a$
`a`because $10^0=1$100=1.

Express $63300$63300 in scientific notation.

**Think:** We need to express the first part of scientific notation as a number between $1$1 and $10$10 and then work out the exponent of $10$10 required to to make the number equivalent.

**Do:**

To find the first part of our scientific notation we place the decimal point after the first non-zero number, so$a=6.33$`a`=6.33.

To find the power of ten, ask how many factors of ten bigger is $63300$63300 than $6.33$6.33?

$63300$63300 is $10000$10000 or $10^4$104 times bigger than $6.33$6.33. (You can also see this by counting how many places the decimal point has shifted). So in scientific notation, we would write this as $6.33\times10^4$6.33×104.

Express $0.00405$0.00405 in scientific notation.

**Think:** We need to express the first part of scientific notation as a number between $1$1 and $10$10 and then work out the exponent of $10$10 required to to make the number equivalent.

**Do:**

To find the first part of our scientific notation we place the decimal point after the first non-zero number, so$a=4.05$`a`=4.05.

To find the power of ten, ask how many factors of ten smaller is $0.00405$0.00405 than $4.05$4.05?

$0.00405$0.00405 is $1000$1000 or $10^3$103 times **smaller** than $4.05$4.05. (You can also see this by counting how many places the decimal point has shifted or the number of zeros including the one before the decimal point). So in scientific notation, we would write this as $4.05\times10^{-3}$4.05×10−3.

We will often use our calculator to evaluate expressions with scientific notation. However, knowing our exponent laws we can manipulate calculations that are relatively straightforward or estimate the size of answers for more complex calculations.

Use exponent laws to simplify $2\times10^6\times6\times10^5$2×106×6×105. Give your answer in scientific notation.

Simplifying first we find:

$2\times10^6\times6\times10^5$2×106×6×105 | $=$= | $12\times10^{6+5}$12×106+5 |

$=$= | $12\times10^{11}$12×1011 |

Then we need to adjust our answer to obtain scientific notation, as the first number is larger than ten.

$12$12 can be as expressed as $1.2\times10^1$1.2×101. We will use this to write our answer in scientific notation.

$1.2\times10^1\times10^{11}$1.2×101×1011 | $=$= | $1.2\times10^{1+11}$1.2×101+11 |

$=$= | $1.2\times10^{12}$1.2×1012 |

Use exponent laws to simplify $\frac{4\times10^{-5}}{16\times10^4}$4×10−516×104. Give your answer in scientific notation.

If we round to $1$1 significant figure, sound travels at a speed of approximately $0.3$0.3 kilometres per second, while light travels at a speed of approximately $300000$300000 kilometres per second.

Express the speed of sound in kilometres per second in scientific notation.

Express the speed of light in kilometres per second in scientific notation.

How many times faster does light travel than sound?

Calculators will often display numbers in scientific notation but the format may vary between different models. A common variation from showing $2.95\times10^8$2.95×108 is the display $2.95$2.95E$8$8 where the E is for exponent of $10$10. Most calculators will also have a button for entering numbers in scientific notation. This may look like $\times10^x$×10`x` or like the button EXP circled in blue in the picture. Look carefully at your calculator and ensure you are familiar with the display format and syntax for entering numbers in scientific notation.

For example, to write $1.5\times10^9$1.5×109 on this calculator, you would press:

Evaluate $\frac{6.45\times10^9\times4.3\times10^{-3}}{8.3\times10^4}$6.45×109×4.3×10−38.3×104.

Give your answer in scientific notation, correct to four decimal places.

Analyse, through the use of patterning, the relationship between the sign and size of an exponent and the value of a power, and use this relationship to express numbers in scientific notation and evaluate powers.