SI Units and Wave Terminology

SI Units

• Hertz (Hz) is the unit for frequency (cycles per second)
• Meters (m) is the unit for distance (wavelength)
• Seconds (s) is the unit for time
• Meters per second (m/s) is the unit for speed (wave speed)

Terminology and Definitions

• Oscillations are repeated back-and-forth motions.
• Vibrations are rapid particle movements within a medium.
• Frequency is the number of oscillations per second, measured in Hertz (Hz).
• Wavelength is the distance between consecutive crests or troughs.
• Speed is the rate of wave travel, measured in meters per second (m/s).
• Energy propagation is the movement of energy through a medium as waves.
• Medium is the material that a wave travels through (e.g., air, water).
• Amplitude is the maximum displacement from rest position (related to wave height).
• Time period is the time for one complete oscillation, measured in seconds.

Transverse Waves

• Particle motion is perpendicular to energy propagation (up and down motion).
• Examples include light waves, water waves, and waves on a string.

Longitudinal Waves

• Particle motion is parallel to energy propagation (back and forth motion).
• Examples include sound waves, shock waves, and pressure waves.

Wave Equation

• Wave speed (v) equals frequency (f) multiplied by wavelength (λ).
• Formula: v = f × λ

Time Period/Frequency

• Time period (T) is the time for one oscillation.
  • Formula: T = 1 / f
• Frequency (f) is the number of oscillations per second.
  • Formula: f = 1 / T

Wave Behaviour

• Reflection is when a wave bounces off a surface.
• Refraction is when a wave changes direction passing from one medium to another (due to a change in speed).
• Diffraction is when waves spread out passing through a gap or around obstacles.
• Diffraction is more pronounced with smaller apertures and larger wavelengths.

Sound

• Sound is produced by vibrating objects and needs a medium to transmit.
• Sound speed is calculated as speed = distance/time.
• A practical technique involves using two microphones to measure sound velocity.
• The human hearing range is approximately 20 Hz to 20,000 Hz.
• Noise is unwanted or unpleasant sound.

Cathode Ray Oscilloscope (CRO)

• CROs are used to measure time period (one complete oscillation) by using the time base setting.
• Frequency can be calculated using f = 1 / T.
• CROs can display waveforms of various sound sources, including musical instruments.

Types of Waves in a Ripple Tank

• Reflection, refraction, and diffraction behaviours are observed similar to other wave types.

Reading a CRO

Understanding the Display

• The CRO displays waveforms with:
  • Horizontal axis (X-axis): representing time (ms or μs per division)
  • Vertical axis (Y-axis): representing voltage (V or mV per division)

Adjusting Controls

• Time base (X-axis): Adjust the rate at which the signal moves, affecting the scale (higher/smaller values for higher signals, lower/larger for slow signals)
• Voltage (Y-axis): Adjusts to vertically compress/stretch the waveform according to the voltage scale.

Reading the Signal

• Frequency: Measured by the time period (T) for one cycle, using the formula f= 1/T
• Amplitude: Measured from the baseline to the peak or trough of the wave.
• Wavelength: Found by counting the horizontal divisions between crests and multiplying by the time base setting.

Cursor Function

• Modern oscilloscopes feature a cursor function allowing for direct measurement of time periods and amplitudes.

Triggering

• Crucial for stable waveform display by synchronizing the waveform.

Determining Values

Amplitude

• Step 1: Observe the vertical scale markings (mV/div or V/div).
• Step 2: Count the vertical divisions from baseline to peak.
• Step 3: Multiply the number of divisions by the gain to get amplitude.

Time Period

• Step 1: Observe the horizontal scale markings (ms/div or s/div).
• Step 2: Count the horizontal divisions for one complete cycle.
• Step 3: Multiply the number of divisions by the time base to get time period.

Frequency

• Use the formula: f = 1 / T

Formulas Summary

• Amplitude = Number of divisions × Gain
• Time Period (T) = Number of divisions × Time Base
• Frequency (f) = 1 / Time Period (T)

Test your knowledge on SI units related to waves, their terminology, and the definitions of key concepts such as frequency, wavelength, and speed. This quiz covers essential terms and principles related to oscillations and energy propagation in various mediums.