In previous lesson, we have discussed measurement, including error, consistency, accuracy and sensitivity. In this lesson, we will proceed to measuring instrument.
In measuring instrument, we will cover vernier caliper, micrometer, stopwatch, ammeter, voltmeter and thermometer.
In this lesson, we will focus on Vernier caliper, where we will discuss the sensitivity of vernier caliper, label of the parts of vernier caliper and function of the parts. We will also learn how to take reading from a vernier caliper, including how to read the main scale and the vernier scale, and also how to determine the zero error from a vernier caliper.
In order to use Vernier caliper to make measurement, placed the object in the inside jaw or outside jaw of the caliper and then slide the vernier scale until the object is held firmly between the jaws. The reading of the measurement is the sum of the reading of main scale and Vernier scale.
For example, in the image above, the reading of the main scale is 4.4cm and the reading of Vernier scale is 0.00cm. Therefore, the reading is 4.4 + 0.00 = 4.40cm. In the very next slide, we are going to discuss how to take reading from the main scale and Vernier scale.
The reading on the main scale is determined with reference to the “0” mark on the vernier scale. Let’s see the example below. The “0” mark is pointing at 0.8 cm of the main scale. Therefore, the reading of the main scale is 0.8cm.
The reading of the vernier scale is indicated by the mark on the vernier scale coincides with any mark on the main scale. In this case, the mark “3” coincidence with the lines on the main scale. Each division on the vernier scale represents a length 0.01cm. Therefore, the reading of the vernier scale is 0.03cm.
As a result, the reading of the vernier caliper is 0.80cm + 0.03cm = 0.83cm.
Zero Error of Vernier Caliper
As we have learned before, a zero error arises when the measuring instrument does not start from exactly zero.
The diagram above shows the reading on a Vernier caliper when the jaw of the caliper is closed firmly. We can see that the reading of the main scale is zero and the reading on the vernier scale is also zero. In this case, we say the caliper has no zero error.
Let’s see another case. The diagram above shows the reading on a vernier caliper when the jaw of the caliper is closed firmly. We can see that the reading of the main scale does not start from zero. Instead, the reading is slightly higher than zero, which means the caliper is subject to positive zero error.
The vernier scale registers a reading of 0.02cm. Therefore, the zero error is +0.02cm. A positive zero error is read from the zero mark on the left hand side of the Vernier scale.
Let’s see another case. The diagram above shows the reading on a vernier caliper when the jaw of the caliper is closed firmly. We can see that the reading of the main scale does not start from zero, too. Instead, the reading is slightly lower than zero, which means the caliper is subjected to negative zero error.
The Vernier scale registers a reading of 0.07cm. A lot of students will think that this is the zero error. Well, actually, this is not the negative zero error. A negative zero error must be read from the “0” mark on the right hand side on the vernier scale. In this case, the zero error is -0.03cm.