In previous lesson, we have discussed micrometer. In this lesson, we will discuss a few more measuring instruments, namely: stopwatch, ammeter, voltmeter and thermometer.

In stopwatch, we will discuss 2 types of stopwatch: the analogue stopwatch and the digital stopwatch. We will also discuss the sensitivity of stopwatches and how to take reading from a stopwatch.

In voltmeter and ammeter, we will discuss how a voltmeter and ammeter is connected to a circuit. Under thermometer, we will discuss the sensitivity of thermometers and the precaution steps need to be taken when using a thermometer.

There are 2 types of mercury thermometer used in school science lab, one with range -10^{o}C – 110^{o}C and another one with range 0^{o}C – 360^{o}C.

The sensitivity of the one with range -10^{o}C – 110^{o}C is 1^{o}C while the sensitivity of the thermometer with range 0^{o}C – 360^{o}C is 2^{o}C.

### Stopwatches

Sensitivity of digital and analogue stopwatches are different. The sensitivity of normal school use digital stopwatches is 0.01s. Sensitivity of analogue stopwatches are much lower than this.

There are 2 types of analogue stopwatches, one with sensitivity of 0.2s and one with sensitivity of 0.1s. This is the stopwatch of sensitivity 0.2s. Take notes that the pointer makes 1 revolution in 60s or 1 minute. Let’s have a closer look at the stopwatch. We can see that there are 5 divisions in every one second, which means each division gives a reading of 0.2s. Therefore the sensitivity is 0.2s.

Let’s see the analogue stopwatch of sensitivity 0.1s. Take notes that the pointer makes 1 revolution in 30s. Let’s have a closer look at the stopwatch. We can see that there are 10 divisions in every one second. Therefore, each division gives a reading of 0.1s. The sensitivity is 0.1s.

There are 2 scales in an analogue stopwatch: the minute scale and the second scale. The minute scale give the reading of minute and the second scale give the reading of second. For example, in the stopwatch above, the minute scale shows a reading of 4 minutes while the second scale shows a reading of 14.4s. Therefore the reading of the stopwatch is 4 minutes and 14.4s.

Let’s see another example. In this stopwatch, the minute scale shows a reading of 1.5 minute while the second scale shows a reading of 17.2s. 1.5 minute is equal to 1 minute 30s. Therefore, the reading of the stopwatch is 1 minute 30 seconds + 17.2s, which is equal to 1 minute 47.2s.

One of the common mistakes when students taking reading from a stopwatch is they overlook the minute scale. They just take the reading from the second scale, but ignore the reading of the minute scale. So, every time when you take a reading, check whether there is any reading at the minute scale.

You should have learned how to convert seconds to minutes or minutes to second in primary school. However, I believe that most of you do not realize that you can also do the conversion by using your scientific calculator.

The conversion of unit of time can be done by using the key “degree, minute and second”. The idea is pretty simple. Let’s compare the unit of angle with the unit of time. This is the symbol used for degree, minute and second. 1 degree = 60 minutes, and 1 minute = 60 seconds.

How about time? For time, 1 hour = 60 minutes, and 1 minute = 60 seconds. Can you see that? Amazingly, they are actually the same. In the operation or conversion of unit of time, what you need to do is just assume that the degree is equivalent to hour. In the very next slide, we are going to discuss how to convert the time in seconds to hour, minute and seconds.

Let’s see this example. 8266s is equal to how many hours, minutes and seconds.

Let’s see how to do this by using your scientific calculator. Before we start, we should keep in mind that we assume 1 degree is equal to 1 hour. In the calculator, we key in 0 hour, 0 minute, 8266 seconds, and then press equal. We get the answer. 8266s is equal to 2 hours, 17 minutes, 46 seconds.

After this, we are going to discuss how to convert hours to minutes or seconds.

Let’s see another example. 2 hours 54 minutes and 26 seconds is equal to how many seconds?

Before we start, we need to know that 1 hour is equal to 60 minutes times 60 seconds, which is equal to 3600 seconds. In order to convert hours to seconds, we multiply the time by 3600s. Let’s see how to do this in a calculator.

Let’s key in 2 hours 54 minutes 26 seconds. In order to convert this time to second, we times 3600, and then press equal. 2 hours 54 minutes 26 seconds is equal to 10466 seconds.

### Thermometer

There are 2 types of mercury thermometer used in school science lab, one with range -10^{o}C – 110^{o}C and another one with range 0^{o}C – 360^{o}C.

The sensitivity of the one with range -10^{o}C – 110^{o}C is 1^{o}C while the sensitivity of the thermometer with range 0^{o}C – 360^{o}C is 2^{o}C.

### Ammeter and Voltmeter

Ammeter is a measuring instrument used to measure electric current in a circuit. The circuit symbol of an ammeter is a circle with a letter A inside. An ammeter must be connected in series in an electric circuit.

Voltmeter is a measuring instrument used to measure voltage or potential difference in a circuit. The circuit symbol of an ammeter is a circle with a letter V inside. A voltmeter must be connected in parallel in an electric circuit.