#### Answer

$4.78\times10^{-6}$

#### Work Step by Step

To convert a number from standard notation to scientific notation, we must move the decimal to the left or to the right, counting the number of places, until the number is between $1$ and $10$, and multiply by a power of $10$. If the number is less than $1$, and we moved the decimal to the right, the power of $10$ is the negative number of places we moved the decimal point. If the number is greater than $1$, and we moved the decimal to the left, the power of $10$ is the positive number of places we moved the decimal point.
To convert the number $0.00000478$ to scientific notation, we move the decimal place $6$ places to the right, which means the power of $10$ will be $-6$.
This gives us the expression $4.78\times10^{-6}$