Unit and Measurement MCQ question and answer with solution | Physics Gk MCQs

Therm is a unit specifically used to measure a quantity of heat or thermal energy.
Think of it like this:
Power is how fast energy is used (like horsepower in a car).
Heat is the total amount of thermal energy.
Light is a form of electromagnetic radiation.
Distance is how far apart two points are.
So, while power involves energy, a 'therm' directly quantifies the amount of heat.

Let's break down the options:
Option A: Weight and Velocity - Velocity is measured in meters per second (m/s), not Newtons.
Option B: Weight and Force - This is the correct answer.
Option C: Weight and Mass - Mass is measured in kilograms (kg), not Newtons.
Option D: Weight and Acceleration - Acceleration is measured in meters per second squared (m/s²), not Newtons.

Newton's Second Law of Motion states that Force (F) = Mass (m) x Acceleration (a). The unit of force derived from this equation is the Newton.
Weight is a type of force, specifically the force of gravity acting on an object's mass. Therefore, weight is also measured in Newtons.

Therefore, the correct answer is B: Weight and Force.

Why Option A is incorrect: Physical quantities are measurable by definition. If a property cannot be measured, it cannot be classified as a physical quantity.

Why Option B is incorrect: Physical laws are expressed using physical quantities, but the quantities themselves are not defined by being expressible as a law. For example, mass, length, and time are physical quantities, but they are not laws in themselves.

Why Option C is correct: Every physical quantity can be described completely with a numerical value (magnitude) and a suitable unit of measurement. For instance, 20 kg means "20" is the magnitude and "kg" is the unit—this fully represents the physical quantity (mass).

Why Option D is incorrect: Since option B is not a defining characteristic, both B and C together cannot be correct. Only C correctly describes physical quantities.

Conclusion: A physical quantity is fully defined by its magnitude and unit, so the correct answer is Option C.

a. Earthquake → 2. Seismograph
A seismograph is an instrument used to detect and record seismic vibrations and waves produced by earthquakes.

b. Altitude (Height) → 3. Altimeter
An altimeter is an instrument used to measure the altitude or height of an object above a reference level, usually mean sea level.

c. Electric current → 1. Ammeter
An ammeter is an instrument used to measure the electric current flowing through a circuit. The SI unit of electric current is the ampere (A).

d. Resistance → 4. Ohm
The ohm (Ω) is the SI unit of electrical resistance. Resistance is the opposition offered by a conductor to the flow of electric current.

Thus, the correct matching is a-2, b-3, c-1, d-4.

Hence, Option A is the correct answer.

A hygrometer is an instrument used to measure the humidity of the air, that is, the amount of water vapour present in the atmosphere.

Option A: Heat
Incorrect. Heat is a form of energy and is measured using appropriate temperature or calorimetric methods, not a hygrometer.

Option B: Humidity
Correct. A hygrometer measures humidity, commonly expressed as relative humidity in percentage (%).

Option C: Force
Incorrect. Force is measured using a force meter or spring balance, and its SI unit is the newton (N).

Option D: Radiation
Incorrect. Radiation is measured using instruments such as radiometers or radiation detectors, depending on the type of radiation.

Hence, Option B — Humidity is the correct answer.

To determine which option is not correctly matched, let's analyze each option:

Option A: Decibel ⟺ Unit of sound intensity
This is correct. The decibel (dB) is indeed the unit used to measure the intensity of sound.

Option B: Horsepower ⟺ Unit of power
This is also correct. Horsepower (hp) is a unit of power commonly used to measure the output of engines and motors.

Option C: Nautical miles ⟺ Unit of naval
This is incorrect. Nautical miles (nmi) are a unit of distance, not a unit specifically related to naval operations. Naval operations may use nautical miles for distance measurements, but nautical miles themselves are not a unit of naval.

Option D: Celsius ⟺ Unit of heat
This is incorrect. Celsius (°C) is a unit of temperature, not a unit of heat. Heat is measured in joules or calories.

Therefore, the option that is not correctly matched is Option C.