Frequency and Period
Frequency is cycles per second; period is the time per cycle.
About this topic
Frequency f is the number of complete cycles per second, measured in hertz. Period T is the time for one cycle, T = 1/f. A 50 Hz wave has a period of 0.02 s.
In waves, f is set by the source and stays constant across boundaries, while speed and wavelength change. Audible sound ranges from about 20 Hz to 20 kHz, mains electricity in many countries is 50 or 60 Hz, and visible light has frequencies near 5 × 10¹⁴ Hz. Higher-frequency waves carry more energy for light, and give higher pitch for sound.
Worked example: a pendulum that swings 30 times in a minute has f = 30/60 = 0.5 Hz and T = 2 s. A guitar string at 440 Hz vibrates once every 1/440 ≈ 0.0023 s, about 2.3 ms. A heartbeat of 72 beats per minute is 1.2 Hz. Radio station frequencies such as 100 MHz mean 100 million cycles per second.
Always check units: 1 kHz = 1000 Hz and 1 MHz = 1,000,000 Hz. Common mistakes include confusing frequency with speed, and forgetting that frequency and period are reciprocals. Frequency can be found on an oscilloscope screen by measuring the period between peaks and taking its inverse.
Key ideas
- f = 1/T
- Unit: hertz
- Pitch depends on frequency
Quick check
Use cases: where Frequency and Period helps
- Homework: review the key idea behind Frequency and Period before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Frequency and Period without notes.
- Visual learning: play with the interactive lab to see how Frequency and Period changes when you adjust its inputs.
- Teaching a friend: explain Frequency and Period in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Frequency and Period?
Frequency is cycles per second; period is the time per cycle.
What will I learn in Frequency and Period?
f = 1/T. Unit: hertz. Pitch depends on frequency.
Is Frequency and Period part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Frequency and Period lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Frequency and Period?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.