Magnetic resonance imaging (MRI) Electromagnets Ultrasound Endoscope Optical fibres Total internal reflection
Look for the signs
There are five common vital signs that are measured to determine body function. Research what these are.
Thermistors in action
A thermistor is connected in series with a variable resistor and a buzzer all powered by a 6 V battery, as shown in Fig. 20.2.2.
At the outset, the thermistor is at room temperature and the buzzer is not sounding.
1. Predict what will happen when the thermistor is heated with a hairdryer. Explain the reasons for your predictions.
Buzzer
2. Set up this circuit and heat the resistor with a hairdryer. Record your observations.
Fig. 20.2.2 Series circuit including a thermistor and buzzer
3. Explain why your predictions did or did not match your observations.
Adjusting the variable resistor changes the overall resistance of the circuit. A student would like to be able to adjust the circuit so that the thermistor will sound the buzzer when the temperature goes above 38 °C. At this body temperature, a person would have a fever.
4. Plan, design, carry out and write up the investigation you would conduct to achieve this task. 352 352 Thermistor Variable resistor
Physics and Health Learning Intentions
In this topic we are learning to: z Produce an electric circuit that can be used to monitor body temperature.
z Describe how ultrasound and MRI scanning work.
When a person is feeling unwell, two of the first things checked are their temperature and heart rate. These measures of general health are known as vital signs.
One device that can be used to measure vital signs is a thermistor. Thermistors
A thermistor is a device whose resistance decreases when it is heated. When a thermistor is connected in a circuit and heated, it causes an increase in current.
A thermistor can be used as an electronic thermometer or as a temperature alarm.
