Physical Quantities and Their Measurements
Knowledge-based Questions
Question 1: What is vernier constant?
Answer: The difference between the smallest main scale division and the Vernier scale division is called Vernier constant.
Question 2: What is dimension?
Answer: The power of fundamental quantities in a physical quantity is called its dimension.
Question 3: What is least count of a screw gauge?
Answer: If the circular scale is rotated only one division the distance that the screw covers for that one rotation is said to be least count of the screw gauge.
Question 4: What is fundamental unit?
Answer: A fundamental unit is that which is independent of any other unit or which can neither be changed nor can be related to any other fundamental unit.
Question 5: What is screw pitch?
Answer: The displacement after one unit rotation of the circular scale that is the length moved along the linear scale that length is called the screw pitch.
Question 6: What is fundamental quantity?
Answer: The seven quantities which are independent and are used to measure other quantities are called fundamental quantities.
Comprehension-based Questions
Question 1: Why are units required to express the amount of a quantity?
Answer: Every physical quantity belongs to a standard unit. A quantity is quite meaningless if it is bare of a unit. Without a unit, we cannot say what the quantity belongs to – length, area, volume, mass, density, temperature and so on; we also cannot say how exactly long a stick is — 10 meters or 10 centimeters, we cannot say the real temperature of an object – 12°C or 12°F if the unit (Celcius or Fahrenheit) is not included.
Question 2: Why weight and mass are not the same type of quantity?
Answer: Mass is a unique property of an object. Mass is a measure of how much matter an object has. It is independent of place, time, and person. Weight is the force exerted on a body by gravity. It is a measure of how strongly gravity pulls on that matter. If the mass of a body is m and gravitational acceleration is g in a place, then the weight of that body in that place is w = mg. For a specific/certain object, the mass of that object is specific. On the other hand, as gravitational acceleration ‘g’ varies with places, so, the weight will not be the same in different places.
Question 3: Why screw gauge is more acute than slide calipers in case of measurement?
Answer: As compared to slide calipers, the screw gauge is more precise because the least count of slide calipers is 0.1 mm and for screw gauge, it is 0.01 mm. So, a screw gauge can measure more precisely than a slide caliper.
Question 4: Write down two differences between fundamental and derived quantities.
Answer: Two differences between fundamental and derived quantities are given below:
Fundamental Quantity | Derived Quantity |
1. The quantities that require no other quantities to express themselves are called fundamental quantities.
| 1. The quantities that are expressed using one or more fundamental quantities are called derived quantities. |
2. Example: mass, time, length, etc. | 2. Example: force, velocity, etc. |
Question 5: Why it is necessary to know the dimension of a quantity? Explain.
Answer: Dimensions are independent of the unit system being used. Hence, they can be used to convert a physical quantity from one unit system to another. They help derive the formulae for physical quantities and the relationship between quantities of an equation.
Question 6: Why slide calipers are more suitable for accurate measurement of an object than meter scale?
Answer: Slide calipers are more suitable for the accurate measurement of an object than a meter scale because it can accurately measure smaller values than a meter scale.
Meter scale has a least count of 1 mm, where least count means the lowest value it can measure accurately. However, slide calipers has a least count of 0.1 mm. So, it can accurately measure the fraction of a millimeter, which a meter scale cannot. Therefore, slide calipers are more suitable for accurate measurement.
Question 7: What do you mean by pitch of a screw gauge is 0.01 mm? Explain.
Answer: The pitch of a screw gauge 0.01 mm means after a complete rotation of the screw, the screw with the attached scale may advance by 1mm. Where the circular part of the screw, by the rotation of which the screw moves forward or backward is divided into 100 equal parts.
Question 8: Explain the necessity of the dimensions of the equation.
Answer: Dimensions in equation helps us to derive relationships between physical quantities. It helps us to check for the accuracy of the equation as well as to derive the unit or dimension of the constants used in the relation.