'A' Level Medical Option Questions - The Heart - ECG
Q2. Electrodes are attached to the chest of a healthy person and a normal ECG waveform is obtained.
(a) State two ways of ensuring good electrical contact between the electrodes and the person.
- electrodes must be made from a material which does not become polarised
- electrodes must be coated with conducting gel
- hair and dead skin must be removed from the patient
2 marks maximum
(b) State two properties of the amplifier needed to amplify the signal from the electrodes.
The amplifier nust have:
- high gain
- high input impedance
- low noise
- frequency response should be even across the frequency range
2 marks
(c) Sketch, on the axes below, the waveform that you would expect to obtain. Label the axes with appropriate scales.
- see graphic for suitable shape
- see graphic for suitable values marked on the axes
Mark on the waveform where the following occur:
(i) atrial depolarisation - see graphic
(ii) ventricular depolarisation - see graphic
(iii) ventricular repolarisation. - see graphic
5 marks
Total 9 marks
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