Units of Measurement Questions

Measurement is nothing but a process of associating numbers with physical quantities and the phenomenon. Measurement is the most fundamental concept in science. In 1790, the metric system was introduced in France. It was France’s first standardised measurement system. Now, it is the standard form of measurement, which is accepted in every country except the United States. There are seven central base units of measurement, and they are:

1. Length – Metre
2. Mass – Kilogram
3. Temperature – Kelvin
4. Amount of substance – Mole
5. Luminous intensity – Candela
6. Electric current – Ampere
7. Time – Second

The unit derived from these seven base units is determined by the International System of Units called SI-derived units. These derived units are dimensionless or can be described as a product of one or more base units. A suitable power of exponentiation can also scale them.

Read More – Units of Measurement

Important Questions with Answers

1. What is meant by dimensionless units?

Dimensionless units are the dimensionless values that act as a unit of measurement for describing different quantities, such as steradians for solid angels.

2. What are the fundamental units of measurement and derived units?

Fundamental units: The units dependent on any other unit are known as fundamental units. Examples: Metre, Kilogram, Second, Ampere, etc.

Derived unit: The units obtained by dividing or multiplying one or more fundamental units with or without introducing any other units are known as the derived unit. Example: Hz, rad, N, F, etc.

3.The speed of light is ________.

1. 299,792,458 m/s
2. 299,792,458 km/s
3. 499,792,458 km/s
4. 499,792,458 m/s

Answer: a. 299,792,458 m/s

Explanation: The speed of the light in the vacuum is 299,792,458 m/s.

4. How many base units are there? Explain each of them.

There are seven base units of measurement.

• Length – Metre

Metre, a unit of length, is described as the distance of the path travelled by light in a single interval of precisely 1/299792458 seconds. The metre is fully based on the velocity of light in a vacuum which is c = 299,792,458 m/s. The symbol of the metre is ‘m’.

• Electric Current – Ampere

Ampere or amp is the unit of electric current in the SI system. The value of 1 Ampere is equivalent to the 6.2415 x 10¹⁸ electrons’ worth of charge moving past a point in a second.

• Mass – Kilogram

The kilogram is the mass of a prototype platinum-iridium cylinder kept in Paris, France, at the International Bureau of Weights and Measures. The symbol of the unit of mass is ‘kg’.

• Temperature – Kelvin

The temperature’s SI unit is Kelvin. Kelvin is exactly 1/(273.16) of the thermodynamic temperature of the triple point of water. The symbol of kelvin is ‘K.’

• Amount of Substance – Mole

The amount of any substance’s SI unit is the mole. One mole is defined as the mass of the substance with 6.302 x 10²³ atoms, also called Avogadro’s number.

• Luminous Intensity – Candela

The luminous intensity’s SI unit is Candela (cd). Candela can be described as the luminous intensity in a supplied order of a source with the luminous intensity of 1/ 683 steradian and emits radiation of a consistent frequency of 540 x 10¹² Hz in a particular direction.

• Time – Second

Second is the time carried by 9,192,631,770 periods of oscillations of the light emitted by a caesium-133 atom, reaching the transition between two hyper-fine levels of the ground state. The symbol of the unit of time is ‘s’.

4. What is the system of units?

The system of units is nothing but the whole set of units, including both fundamental and derived units for all physical quantities.

5. What are the advantages of the SI system of units?

In the SI system of units, each physical quantity has only one particular unit. This means it is unnecessary to convert one form of a unit into another format of a unit within the system. There are no conversion factors for learners to memorise.

6. Measurement is a process in which the properties of an object are determined by comparing them to a standard or known quantity.

1. True
2. False

Answer: a. True

Explanations: The given statement is the proper description of the measurement. Measurement is the procedure in which the properties of an entity are determined by comparing them to a standard.

7. The unit of luminous intensity is _______.

1. Metre (m)
2. Newton (N)
3. Candela (cd)
4. Becquerel (Bq)

Answer: c. Candela (cd)

Explanation: Candela (cd) is the unit of luminous intensity. It can be described as the luminous intensity in a provided order of any source with the radiant intensity of 1/ 683 steradian and emits radiation of a consistent frequency of 540 x 10¹² Hz.

8. Becquerel is the unit of ________.

1. Frequency
2. Radioactive decay
3. Electrical capacitance
4. Luminous intensity

Answer: b. Radioactive decay

Explanation: The unit of radioactive decay (decays per unit time) is the becquerel (Bq). This is an example of a derived unit.

9. What is the smallest unit of time?

The smallest unit of time is zeptosecond.

10. Fill in the blank.

The mole is the amount of substance which contains as many entities as there are atoms in ______________ of carbon-12.

1. 0.012 kg
2. 0.012 gram
3. 0.020 kg
4. 0.020 gram

Answer: a. 0.012 kg

Explanation: The mole is the amount of substance which contains as many entities as there are atoms in 0.012 kg of carbon-12.

Practice Questions

1. What is the unit of electrical capacitance?
2. What are the significant figures?
3. What is meant by dimensional units?
4. Define magnetic flux.
5. What is second?

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