Uses of an Oscilloscope (Cambridge O Level Physics)

Displaying Waveforms

• An oscilloscope is a device that can be used to study a rapidly changing signal, such as:
  • A sound wave
  • An alternating current

An Oscilloscope

Oscilloscopes have lots of dials and buttons, but their main purpose is to display and measure changing signals like sound waves and alternating current

• When a microphone is connected to an oscilloscope, the (longitudinal) sound wave is displayed as though it were a transverse wave on the screen
• An alternating current (A.C.) on an oscilloscope is also represented as a transverse wave.
• Using the oscilloscope the frequency and amplitude of these waves can be determined
• The x-axis is the time and the y-axis is the voltage (or y-gain)

 

Measuring P.D. and Time Intervals

• The p.d. can be measured using the oscilloscope's vertical axis called the y-gain
  • This is done by measuring the wave amplitude, by counting the number of squares from the centre of the wave to the peak or trough of the waveform, and applying the correct scale
  • The vertical axis has the units volts per division, volts/div
  • It is possible to adjust the y-gain scale by turning the correct switch on the oscilloscope
  • The y-gain may have a scale of 1 volt per division but by zooming in it is possible to increase the scale to 10 volts per division for example

 

• Short intervals of time can be measured using the oscilloscope's x-axis called the time-base:
  • The time base is how many seconds each division represents measured commonly in seconds per division, s/div, or seconder per centimetre, s/cm
  • Measuring time is done by measuring the time-period of one wavelength, by counting the number of squares from one point on one wave to the equivalent point on the next wave 
  • It is possible to adjust the time-base scale by turning the correct switch on the oscilloscope
  • The time-base may have a scale of 1 second per division but it is possible to increase or decrease the scale by zooming in or out

Wavelength and Amplitude

A sound wave is displayed as though it were a transverse wave on the screen of the oscilloscope. The amplitude can be used to measure the y-gain of the waveform. The time base can be used to measure a full time-period of the wave cycle

Calculating Frequency

• Use as many wavelengths shown on the screen as possible to reduce uncertainties
• Dividing the total time by the number of wavelengths will give the time-period T (time taken for one complete oscillation)
• The frequency is then determined using the equation 

An Example of Counting Wavelengths

An Oscilloscope display showing wavelengths and a time-base setting of 5 ms/div