Physical Quantities and Measurements Short Questions

Question 31

What is parallax error?

Answer:
Parallax error is an error caused by viewing a scale from an incorrect angle. It makes the pointer or object appear at a different scale position.

Question 32

How can parallax error be avoided?

Answer:
Parallax error can be avoided by keeping the eye directly in front of and perpendicular to the scale reading.

Question 33

What is a measuring tape used for?

Answer:
A measuring tape is used to measure lengths ranging from about 1 mm to several metres. It is suitable for objects or distances longer than a metre rule.

Question 34

What are Vernier callipers?

Answer:
Vernier callipers are precision instruments used to measure small external and internal dimensions as well as depth. They can measure lengths down to about 0.1 mm.

Question 35

Name the two scales of Vernier callipers.

Answer:
Vernier callipers have a fixed main scale and a movable Vernier scale. The Vernier scale slides along the main scale.

Question 36

State the functions of the jaws and depth gauge of Vernier callipers.

Answer:
The outside jaws measure external dimensions, while the inside jaws measure internal dimensions. The depth gauge or tail measures the depth of a hollow object.

Question 37

How is the least count of Vernier callipers calculated?

Answer:
The least count is the difference between one main-scale division and one Vernier-scale division. It can also be found by dividing one main-scale division by the total Vernier divisions.

Question 38

How is a Vernier calliper reading determined?

Answer:
The reading equals the main-scale reading plus the product of the coinciding Vernier division and the least count. Any zero correction is then applied.

Question 39

What is zero error in Vernier callipers?

Answer:
Zero error occurs when the zero of the Vernier scale does not coincide with the zero of the main scale while the jaws are fully closed.

Question 40

How is positive zero error corrected in Vernier callipers?

Answer:
When the Vernier zero is to the right of the main-scale zero, the instrument reads more than the actual value. The positive zero error is therefore subtracted from the observed reading.