Reading an a.c. Graph
Reading an a.c. Graph
- Three measurements describe the timing and size of a repeating waveform: peak value, period and frequency.
Peak, period and frequency
Definition
1 markWhat is meant by frequency?
Model answer: The number of complete cycles per unit time.
- The peak value is the greatest magnitude reached. Measure it from the zero line, not from trough to peak.
- The period is the time for one complete cycle. Its symbol is and its unit is the second.
- The frequency is the number of complete cycles each second. Its unit is the hertz, Hz.
Symbols
- = frequency (Hz)
- = period (s)
Read vertical and horizontal scales separately
Swipe left or right to see the whole diagram →
- Find the centre line. This is the zero-value line.
- Measure vertically from zero to a peak to obtain the peak value.
- Measure horizontally from one point to the next matching point to obtain the period.
- Convert the period to seconds, then find the frequency.
Common mistake
A positive peak to the next negative peak is only half a cycle. Use two successive positive peaks, or two successive upward zero crossings, for one period.
Your turngraph check
An a.c. graph has a peak current of 4.0 A. Successive positive peaks are 25 ms apart. State the peak current, period and frequency.
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Answer