Vernier Zero Error and its Correction

Vernier Zero Error and its Correction

Consider a rod whose actual length is 3.25 cm. To measure the length of the rod experimentally we use a sca1 graduated in cm. We take a large number of readings. Suppose the average value of length comes to be 3.28 cm. The measured value does not coincide with the actual value of the length. We say that there is an error in our measurement. The magnitude of the error is 0.03 cm.

On closing the jaws, if the zero of the main scale coincides with the zero of the vernier scale then the instrument has no zero error and no correction is required. If the zero of the vernier scale does not coincide with the zero of the main scale, then there is zero error and zero correction is required. The zero error may be positive or negative. If the zero of the vernier scale is on the right of the zero of the main scale, the zero error will be positive, because the observed value measured is more than the actual value. So the difference is to be subtracted from the observed value. To calculate the positive zero error, look at the vernier scale and note the number of divisions of the vernier scale which coincides with any of the main scale divisions and multiply this number by the least count. Suppose 5th division of the vernier scale coincides with one of the main scale divisions, then the zero error is +0.05cm and the zero correction is —0.05cm. In this case the zero correction is negative.

If the zero of the vernier scale is on the left of the main scale zero, then t measured value is less than the actual value. So the difference is to be added to the observed value. This zero correction is positive.

To find the negative zero error note the number of vernier scale division which coincides with any of the main scale division. If, say, it is 4, then the zero error will be —(10—4) x 0.01 = —O.0&m. In this case zero correction is positive.

To measure the length of an object, it is placed between the two jaws of the vernier calipers. The distance between the zero of the main scale and the zero of the vernier scale is equal to the length of the object. Note the main scale reading just before the zero of the vernier scale. Note the number of vernier scale division which coincides with one of the main scale divisions. Multiply this number by the least count. This will give vernier scale reading, it is known as fractional part. Acid main scale reading and fractional part. This is the length of the object. If there is zero error, adjust it to get the correct length of the object.