9th Class Physics Notes “Zero Error”

Zero error:

When the jaws of the verniercalliper are closed, and the zero of main scale and zero of vernier scale do not coincide with each other, there is error in the verniercalliper known as zero error.

Type of zero error:

1. Positive zero error
2. Negative zero error
3. Positive zero error:

When the zero of the vernier scale on the right of the zero of the main scale then error is known as positive error as shown in figure.

Figure:

positive zero error in vernier calliper

Positive zero error correction:

For correction of reading the positive error is subtracted from the final measurement taken by the instrument.

2. Negative zero error:

When the zero of the vernier scale on the left of the zero of the main scale the error is known as negative error as shown in figure.

Figure:

negative zero error in vernier calliper
Negative zero error correction:

For correction of reading the negative error is added to the final measurement taken by the instrument.

Measurement with vernier calipers:

Let we want to measure the diameter of a small solid cylinder we will use the following method.

1. Close the jaws of vernier calipers, if the zero of vernier scale coincide with the zero of main scale, then there is no error.
2. Now place the solid cylinder b/w the jaws of vernier calipers and tight the jaws.
3. Note the reading on main scale suppose the zero of vernier scale is to the left of 2cm and to the right of 1.9cm. Thus the length is greater than 1.9cm. Note this reading as main scale i.e. main scale reading = 1.9cm
4. To find the fraction to be added to 1.9cm. We see that what division of vernier scale coincide with any division of main scale. Suppose 6th division of vernier scale coincide with 2nd division of the main scale.
5. Multiply least count (0.01cm) with 6. This is vernier scale reading i.e. vernier scale reading = 6 x 0.01cm vernier scale reading = 0.06cm
6. Add main scale reading and vernier scale reading. final reading = main scale reading + vernier scale reading final reading = 1.9 + 0.06 final reading = 1.96cm

For zero correction:

If there is zero error in the instrument then we have correct reading as;

correct reading = 1.96 ± zero error

Q: Explain the construction and working of screw gauge.

Screw gauge/micro meter:

Definition:

Screw gauge is an instrument which is used to measure the thickness of small objects up to 0.01mm or 0.001cm accurately as shown in figure.

Inventor:

Screw gauge was invented by scientist named William screw.

Purpose of screw gauge:

The vernier caliper can measure the thickness of small object up to 0.01cm, if we want to measure small object from 0.01cm, then for this purpose we use the screw gauge/micrometer, which measure accurately up to 0.01mm or 0.001cm.

Construction:

A screw gauge consists of;

Circular scale

U-shaped frame

Linear scale/main scale