**Q.17: What is vernier callipers? What are its major parts?**

**Ans: VERNIER CALLIPERS:**

Vernier callipers is a meter stick graduated in millimeters used to measure a distance up to 1mm. it can also be used to measure a distance up to 0.05mm.

**PART OF VERNIER CALLIPERS:**

There are four major parts of vernier calllpers.

- Main scale
- Vernier scale
- Jaws
- Thin flat rod

**Main Scale:**

A vernier calliper consists of a rectangular steel bar whose one side is graduated in millimeters each division on the main scale is Imm (0.1cm).

**Vernire Scale:**

A small scale usually consisting of 10 division which slides over the main scale is known as vernier scale.

**Jaws:**

There are two Jaws are present on a vernier calliper which is also called callipers. One is called upper jaw and other is called lower jaw.

**Thin Fiat Rod:**

A thin flat rod is attached to the sliding scale on its back which can measure the internal depth of a hallow cylinder.

**Q.18: Write down the construction and working of vernier calipers?**

**Ans: CONSTRUCTION OF VERNIER CALLIPERS:**

Vernier calliper consists of two parts. The first part consists of a scale called the main scale. The longer lines on the main scale represent centimeters and smaller lines, millimeters. Its left upper part has a jaw “A”. The second part consists of a vernier scale which can slide over the main scale. The left upper part of this scale has a jaw “B”. Jaw “A” is fixed while jaw “B” is movable.

**Working Of Vernier Callipers:**

The diameter of a small spherical object can be measured with the help of this device.Before the measurement close the jaws of the vernier caliper completely and note downwhether the zero line of the vernier scale coincides with the zero of the main scale. If theycoincide, there is no zero error. Open the jaws now and place an object between them.Read the scale division to the left of the zero of the vernier scale and also read the reading of vernier scale note it down in observation table. Again place the cylinder in between the jaws to measure the diameter. Read the main scale and vernier scale reading, note down in the observation table. Repeat the same three times.

**Q.21: Define zero error? Write down its types?**

**Ans: ZERO ERROR:**

It is an error which arises when zeroes of main scale and vernier scale do not coincide with each other upon joining two jaws.

**Types OF ZERO ERROR:**

There are two types of zero error

- Positive zero error
- Negative zero error

**Positive Zero Error:**

If the zero of the vernier scale is on the right of the zero of the main scale the zero error will be positive. The observed value is more than the actual value so the difference is to be subtracted from the observed value.

**Negative Zero Error:**

If the zero of the vernier scale is on the left side of the zero error will be negative. The measured value is less than the actual value so the difference is to be added to observe value.

**Q.22: Define micrometer screw gauge? Write down its major parts?**

**Ans: SCREW GAUGE:**

It is an instrument that can measure small length thickness correctly up to — of a millimeter or up to three place of decimals.

Major Parts:

There are the following parts of screw gauge.

- U-shaped metal frame
- Fixed stud
- Movable stud
- Main-scale
- Circular scale
- Drum
- Ratchet

**Q.25: Define zero error of screw gauge and its types?**

**Ans: ZERO ERROR:**

When we close the two studs of the screw gauge if the zero of the circular scale has advanced beyond the zero line of the main scale or left behind the zero of the main scale there is zero error.

**Types OF ZERO ERROR:**

There are two types of zero error.

- Positive zero error
- Negative zero error

**Positive Zero Error:**

If the zero of the circular scale is below the horizontal reference line the zero error is positive. The observed value is more than the actual value. Note the number of division on the circular scale from zero which coincides with the reference line. Multiply this number by the least count. This is positive zero error which is subtracted from the observed value to get the correct value.

**Negative Zero Error:**

If the zero of the circular scale is above the reference line and the edge of the drum has crossed the zero line of the main scale then the zero error is negative. Note the number of divisions on the circular with the references line multiply it by the least count. This is negative zero error. Add this error to the observed value to get the correct measurement.

**Q.26: Write down the construction of screw gauge?**

**Ans: MICROMETER SCREW GAUGE:**

A micrometer screw gauge measures very small lengths such as the diameter of a wire or sphere. It can measure accurately up to one hundredth part of a millimeter.

**Construction:**

It consists of a U – shaped metallic frame having a fixed stud at A. The other end has a hallow cylinder C. A line is marked on the cylinder parallel to its axis which has a millimeter scale. This cylinder acts as a nut which has a both inside it. The right end of the both is like cap. The both can be rotated with the help of this cap. The left end of this cap has a scale which is usually divided into 100 equal parts (50 division are also found).