Biological Measurement (AQA A Level Physics)

Describe how a heartbeat can be determined from an ECG trace.

The signal from the heart needs to be amplified by an amplifier to be accurately displayed on a screen.

Complete the sentences with the correct words to describe the properties of the amplifier.

• means the amplifier can increase the electrical signal without increasing the

• means the amplifier does not reduce the quality of the electrical signal during the amplification process

• means the amplifier increases the input signal enough so it can be interpreted by the machine

Which statements about ECGs are correct?

Place ticks in the boxes.

State three ways the ECG signal from the heart can be improved.

The graph in Figure 1 shows a normal electrocardiogram (ECG) signal obtained at the surface of the skin of a patient.

Figure 1

Image to be redrawn by graphics

State the amplitude of the main pulse in the signal.

Calculate the pulse rate per minute from the ECG in part (a).

State the changes you would expect to see in the electrocardiogram if the patient began to exercise.

Annotate Figure 1 with a P to show the points where atrial contraction starts and a Q to show the points where ventricular contraction starts.

Different ultrasound techniques are used to investigate the health of a patient’s kidneys.

Figure 1 shows the results of an ultrasound scan of a kidney using one technique.

Figure 1

Identify the type of ultrasound scan used to produce Figure 1. Explain your answer.

Another ultrasound technique is used to measure the speed of blood flow in one of the kidney’s blood vessels.

Figure 2 shows an image formed using this technique. It shows how the speed of flow through the blood vessel varies with time.

Point X shows this speed at one instant of time.

Figure 2

Determine the patient’s heart rate in beats per minute.

An ECG was made for the patient in part (b).

Figure 3 shows one heartbeat from the ECG.

Annotate Figure 3 to show:

• units on both axes

• scales on both axes

• point Y that corresponds to point X on Figure 2.

Figure 3

A backing gel is used between an ECG pad and the skin of the patient.

The gel is sticky. This property ensures that the pad is securely attached to the skin.

Explain:

• one other reason why the backing gel is needed

• one other property of the backing gel

• how the skin is prepared for the pad to be applied.

Sketch a graph on Figure 1 of the ECG trace for a healthy heart. Label each axis with appropriate units and scales.

Figure 1

Mark on the waveform in part (a) where the following occur:

i) atrial depolarisation

[1]

ii) ventricular depolarisation

[1]

iii) ventricular repolarisation

[1]

When obtaining such a trace, electrodes are attached to the patient.

State and explain two precautions which should be taken when attaching the electrodes to ensure reception of the best signal.

The amplifier used to amplify the ECG signal must have a high gain.

State two other properties of the amplifier.