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Figure 1 shows an ultrasound transducer used to perform medical scans - AQA - A-Level Physics - Question 4 - 2020 - Paper 6
Question 4
Figure 1 shows an ultrasound transducer used to perform medical scans. Explain how the transducer in Figure 1 operates in medical diagnosis. In your answer you shou... show full transcript
Worked Solution & Example Answer:Figure 1 shows an ultrasound transducer used to perform medical scans - AQA - A-Level Physics - Question 4 - 2020 - Paper 6
Step 1
Explain how an ultrasound pulse is produced by the transducer.
Answer
The transducer converts electrical energy into mechanical energy through the piezoelectric effect. When a voltage is applied to the piezoelectric crystal, it vibrates and generates an ultrasound pulse. This pulse travels through the surrounding medium.
Step 2
Explain how the reflected ultrasound pulse is detected by the transducer.
Answer
When the ultrasound pulse encounters a boundary, part of it is reflected back to the transducer. The transducer then detects the reflected pulse as a voltage signal due to the reverse piezoelectric effect, converting it back into electrical energy.
Step 3
Explain how the transducer can both transmit a pulse and receive the reflected pulse.
Answer
The transducer alternates between sending ultrasound pulses and receiving reflected echoes. This is possible due to its design, where the piezoelectric crystal can convert electrical energy into ultrasound and vice versa, allowing it to transmit and receive signals effectively.
Step 4
Step 5
Calculate the percentage of the incident ultrasound intensity that is transmitted into the lung tissue.
Answer
The intensity transmission coefficient (T) can be calculated using the formula:
where ( Z_1 ) and ( Z_2 ) are the acoustic impedances of air and lung tissue respectively.
- Acoustic impedance of air: ( Z_1 = density_{air} \times speed_{air} = 1.3 \times 330 = 429 \text{ kg/(m}^2\text{s)} )
- Acoustic impedance of lung: ( Z_2 = density_{lung} \times speed_{lung} = 1075 \times 1580 = 1692250 \text{ kg/(m}^2\text{s)} )
Calculating T:
T \text{ in percentage} = 0.0005069 \times 100 \approx 0.051\%$$Step 6
Discuss whether an ultrasound scan would be suitable to investigate a tumour inside a lung.
Answer
An ultrasound scan is generally suited for soft tissue imaging; however, due to air pockets in the lung, ultrasound may face challenges in penetrating lung tissue properly. The presence of air can significantly attenuate the ultrasound waves, leading to poor imaging quality. Therefore, while ultrasound may provide some information, it may not be the ideal modality for visualizing a tumor in the lung.