Part 05 · Oscillations and waves · Card 2 of 11
Period and frequency
Period is the time for one full cycle. Frequency is cycles per second, in hertz. They are inverses: f = 1/T.
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Analogy
A heartbeat: 60 beats a minute is 1 Hz.
Example
50 Hz mains
T = 1 / fT = 1 / 50T = 0.02 s
In practice
Mains electricity at 50 Hz repeats every 0.02 s.
Practice
Flashcards
- What is the relation between period and frequency?f = 1/T.
Interview questions
- A pendulum clock runs slow on a mountain top. Explain why.
- Period depends on g
- g is slightly smaller at altitude
- Smaller g gives longer period
Questions people ask
What is the difference between frequency and angular frequency?
Frequency f counts cycles per second in hertz. Angular frequency omega counts radians per second, and omega = 2 pi f. One full cycle is 2 pi radians. Equations for oscillations usually use omega, while everyday descriptions of sound and electricity use f.
How do I find frequency from a graph?
Read the time between two matching points, such as two peaks. That is the period T. Then compute f = 1/T. If peaks are 0.25 s apart, the period is 0.25 s and the frequency is 4 Hz. Count more cycles for better accuracy.