Friday, November 4, 2011

Physics Form 5: Chapter 4 - Measuring Voltage and Time Period using Oscilloscope

  • The Y-GAIN (VOLTS/CM) control determines the height of the trace. Choose a setting so the trace occupies at least half the screen height, but does not disappear off the screen.
  • The TIMEBASE (TIME/CM) control determines the rate at which the dot sweeps across the screen. Choose a setting so the trace shows at least one cycle of the signal across the screen.

  • Amplitude is the maximum voltage reached by the signal.
    It is measured in volts, V.
  • Peak voltage is another name for amplitude.
  • Peak-peak voltage is twice the peak voltage (amplitude). When reading an oscilloscope trace it is usual to measure peak-peak voltage.
  • Time period is the time taken for the signal to complete one cycle.
    It is measured in seconds (s), but time periods tend to be short so milliseconds (ms) and microseconds (µs) are often used. 1ms = 0.001s and 1µs = 0.000001s.
  • Frequency is the number of cycles per second.
    It is measured in hertz (Hz), but frequencies tend to be high so kilohertz (kHz) and megahertz (MHz) are often used. 1kHz = 1000Hz and 1MHz = 1000000Hz.
    frequency  =           1             and     time period  =           1        
    time period frequency
Example of measurement:

Measuring Voltage
Voltage = distance in cm × volts/cm
Example: peak-peak voltage = 4.2cm × 2V/cm = 8.4V
amplitude (peak voltage) = ½ × peak-peak voltage = 4.2V

Measuring Time Period
Time = distance in cm × time/cm
Example: time period = 4.0cm × 5ms/cm = 20ms
    and   frequency = 1/time period = 1/20ms = 50Hz

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