Ultrasound Physics Basics: Units, Scientific Notation, Prefixes, Ratios, Decibels

20 Q&A flashcards covering units, scientific notation, metric prefixes, ratios, density, rounding rules, percentages, decibels, and practical conversion tricks relevant to ultrasound physics.

A standard amount universally agreed upon for measuring something.

What is a "unit"?

Second (s).

What is the base unit for time in ultrasound?

Meter (m).

What is the base unit for distance?

To write very large or very small numbers without long strings of zeros.

Why do we use scientific notation?

8.0 × 10^3

Write 8,000 in scientific notation.

5.0 × 10^-4

Write 0.0005 in scientific notation.

The number is greater than 1 (move the decimal point to the left).

A positive exponent in scientific notation tells you…

The number is less than 1 (move the decimal point to the right).

A negative exponent in scientific notation tells you…

Mega (M) – “million.”

What is the prefix for 10^6?

Kilo (k) – “thousand.”

What is the prefix for 10^3?

Milli (m) – “thousandth.”

What is the prefix for 10^-3?

Micro (µ) – “millionth.”

What is the prefix for 10^-6?

Nano (n) – “billionth.”

What is the prefix for 10^-9?

Move the decimal three places to the left (1 kHz = 0.001 MHz).

Trick to convert kHz to MHz.

One number divided by another to show comparison.

In physics, what does “ratio” mean?

Density = mass ÷ volume.

What is the equation for density?

Keep the same number of significant figures as the least precise input value.

What is the general rule for rounding answers (significant figures)?

Per 100 (e.g., 25 % = 25/100).

What does the percent symbol (%) really mean?

A logarithmic scale—every 3 dB doubles intensity.

The decibel (dB) is what kind of scale?

They allow quick reading and comparison of ultrasound specifications (e.g., a 5 MHz probe).

Why is it useful to memorize metric prefixes?