The Sine Wave and Sine Wave Patterns

Question 1

Define sin

Answer 1

Right angle triangle

Sine of angle = opposite side
__________
hypoteneuse

Question 2

Describe the sin graph

Answer 2

X - axis: different angles of angle A

Y-axis: the length of the opposite side to angle A = d

d = opposite side to angle A
r = hypoteneuse adjacent to angle A

d = r Sin A

Morphology –> repeating sin graph

Question 3

What does 90 degrees ‘out of phase mean’

Answer 3

When two sine graphs are compared the degree to which they differ along the X axis (i.e. Angle A) is the degree to which they are ‘out of phase

Question 4

What is the wavelength of a sine wave

Answer 4

The wavelength is the distance between any two corresponding points in successive cycles e.g. The distance between two peaks and troughs

Question 5

WHat is the amplitude of a sine wave

Give practical examples of large and small amplitude waves

Answer 5

The maximum displacement of the wave from the horizontal axis

Sound: LArge amplitude –> loud. Small amplitude = soft

Light: LArge amplitude bright and small amplitude dim

Question 6

Define frequency

Answer 6

The number of complete cycles which occur in one second

Frequency = cycles/seconds

SI unit: hertz (Hz)

e. g. 10 Hz = 10 cycles per second
- -> the time taken for 1 complete cycle is one tenth of a second

Question 7

Define the period of a sine wave

Answer 7

The time taken for one complete cycle

The period is the reciprocal of the frequency

T(period) = 1/f

Question 8

How is the velocity of a wave motion calculated

Answer 8

Velocity = distance/time
Velocity = wavelength/period

Therefore,
Velocity = Wavelength x Frequency

Question 9

What is the velocity of sound

Answer 9

330 m/s

If velocity is fixed then frequency and wavelength are interrelated: the higher the frequency the shorter the wavelength and vice verse

Question 10

What is pitch?

Answer 10

Sound waves with different frequencies are heard with different pitches

Short frequency means long wavelength and low pitch

High frequency means short wavelength and high pitch

Question 11

Describe how the concept of pitch can be paralleled whilst describe the frequency of light

Answer 11

A light with high frequency (and short wavelength) BLUE

A light with lower frequency and longer wavelength: RED

Question 12

Summarize the electromagnetic spectrum including real life examples

Answer 12

EXAMPLE WAVELENGTH

Radio / TV / Radar 10 ( Paging systems)
Microwaves 10^-3 (Definition of a second)
Infrared 10^-6 (Infrared analyzers)
Visible 700 - 380 x 10^-9 (Refracrtometry and oximetry)
Ultra-violet 400 -10 x 10^-9
X-rays 10^-12 (Radiology and radiotherapy)
Gamma rays 10^-15

Question 13

How is 1 second of time defined

Answer 13

The second is defined in terms of the frequency of radiation emitted by atoms of caesium-133.

Question 14

What is the doppler effect?

Answer 14

Sound waves are repeating regions of high an low pressure through the medium that they travel (e.g. air). These waves travel at a constant velocity. The velocity of the sound wave is equal to the wavelength x frequency. This means that as velocity is constant frequency is inversely proportional to the wavelength. High frequency sound waves are heard at high pitch. Low frequency sound waves are heard at low pitch. If the source of a sound is not moving, the wavelength and frequency remain unchanged. As the velocity of the sound wave remains constant, if the source of the sound is moving closer and further away from the ear (or receiver) the wavelength and frequency will vary. As the sound source moves closer the frequency will increase –> higher pitch. As the sound moves further way the frequency will decrease. This change in frequency and pitch is known as the doppler effect and has multiple applications in medical devices.

Question 15

Why does ultrasound gel improve the performance of the ultrasound equipment

Answer 15

When sound waves travel through the boundaries between substances of different densities, some of the sound waves are transmitted through the new density but varying proportions of the sound waves are reflected back to the source and some are scattered. The degree of difference in adjacent substance densities determines the degree of attenuation of ultrasound transmission. Air has a very low density compared to all tissues. This significant density discrepancy leads to pronounced attenuation of the ultrasound waves. Ultrasound gel reduces the difference in densities through which the sound waves travel which greatly improves the performance of the device.

Question 16

Is the doppler effect used to produce images on the monitor of an ultrasound. Substantiate your answer

Answer 16

No. The doppler effect detects the change in frequency of the moving blood cells relative to the probe and generates an audible sound related to the flow velocity.

Images are formed via a different application of ultrasound technology.

1. Ultrasound waves are reflected off boundaries and interfaces between substances of different densities
2. The same transducer is used to transmit and receive the ultrasound waves and is NOT the dopplar effect but the time taken for the ultrasound wave to travel from the transducer and return which allows the depth of boundary or change in density to be measured
3. This mechanical signal is converted into an electrical one via the transducer (containing the piezoelectric crystal) and displayed as an image on a monitor

The probe contains small individual piezoelectric crystals arranged in a line to display a cross section through the body

Question 17

What is a clinical use of ultrasound waves that are absorbed by tissues

Answer 17

Physiotherapy: High intensity ultrasound used by physiotherapists to provide local heating

Question 18

With regard to ultrasound, what is cavitation

Answer 18

If very high power ultrasound is used, the pressure in the sound wave can fall to 0 during the minimum of the waveform and this can result in the rapid creation and collapse of bubbles in tissues, a potentially damaging process known as cavitation.

Question 19

Define interference

Answer 19

The interaction of two or more sine waves and the resulting wave depends on the phase of the two wave motions which interfere

Question 20

How does a refractometer measure the concentration of halothane in Oxygen?

Answer 20

1. Two light beams pass through the refractometer - one through sample chamber (with halothane) other through reference chamber (without halothane)
2. The two beams are combined
3. If in phase - bright fringe produced (amplitudes additive) If out of phase - dark fringe produced (amplitudes subtract). An array of light and dark fringes results.
4. When halothane is added to the SAMPLE chamber it reduces the velocity of light passing through the SAMPLE chamber and alters the phase relationships when the two light beams are recombined
5. So a displacement of fringe pattern occurs which may be observed and measured through an eye-piece.

THE DISPLACEMENT OF A SELECTED FRINGE IS DIRECTLY PROPORTIONAL TO THE CONCENTRATION OF GAS ADDED TO THE SAMPLE CHAMBER

Question 21

What is the important limitation of a refractometer

Answer 21

Calibration required for specific gases/volatiles

Hence cannot identify component gases in a mixture so these must be known in advance.

Question 22

What is an interference filter. give an example of a device in which an interference filter is used.

Answer 22

An optical component used to select one wavelength from a spectrum of wavelengths. Filters of this type are useful for selecting the required wavelength of infrared radiation for use in an infrared analyser

Question 23

What is Fourier analysis? What are the 2 main concepts in Fourier analysis

Answer 23

The mathematical process of analysing complex wave patterns into a series of simpler sine wave patterns. This process helps in understanding the patterns of biological electrical signals

1. Complex wave pattern may be analysed into a large number of sine wave components
2. Sharp spikes mean high-frequency components and smooth rounded patterns consist of a more limited range of frequencies