1
How many base units are there in the International System of Units (SI)?
Correct answer: C. 7
The seven SI base units are the metre, kilogram, second, ampere, kelvin, mole and candela.
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Physics: Units and Instruments MCQs
Solved Everyday Science MCQs on SI units, measuring instruments, light, sound, heat and electricity, with short explanations for competitive exams.
25 MCQsUpdated 27 October 2026
These MCQs cover the SI system and its base units, units of pressure, frequency, power and loudness, units of distance such as the light-year, and instruments such as the anemometer, barometer and thermometer.
Unit and instrument questions are quick to answer once learned. Group them by quantity (pressure, temperature, sound) and note the scientist each unit is named after.
- 2
The SI unit of work and energy is the:
Correct answer: B. Joule
One joule is the work done when a force of one newton moves an object one metre.
easy - 3
The SI unit of power is the:
Correct answer: D. Watt
One watt equals one joule of energy transferred per second.
easy - 4
The SI unit of pressure is the:
Correct answer: B. Pascal
One pascal is a force of one newton spread over one square metre. The bar and the atmosphere are common non-SI units.
easy - 5
The SI unit of electric current is the:
Correct answer: B. Ampere
The ampere is an SI base unit. The volt measures potential difference, the ohm resistance and the coulomb charge.
easy - 6
The SI unit of electrical resistance is the:
Correct answer: B. Ohm
Resistance is measured in ohms (Ω), named after Georg Ohm.
easy - 7
The SI unit of frequency is the:
Correct answer: A. Hertz
One hertz is one cycle per second.
easy - 8
The SI base unit of temperature is the:
Correct answer: A. Kelvin
The kelvin is the SI base unit. 0 K is absolute zero, which is −273.15 °C.
easy - 9
According to Ohm's law, voltage (V) equals:
Correct answer: A. I × R
Ohm's law states V = I × R, where I is the current and R is the resistance.
easy - 10
A light-year is a unit of:
Correct answer: A. Distance
A light-year is the distance light travels in one year, about 9.46 trillion kilometres.
easy - 11
Atmospheric pressure is measured with a:
Correct answer: C. Barometer
A barometer measures air pressure and is used in weather forecasting. A hygrometer measures humidity.
easy - 12
The humidity of the air is measured with a:
Correct answer: D. Hygrometer
A hygrometer measures moisture in the air. An anemometer measures wind speed.
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Wind speed is measured with an:
Correct answer: B. Anemometer
An anemometer, often with spinning cups, measures wind speed. An altimeter measures altitude.
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Electric current in a circuit is measured with an:
Correct answer: C. Ammeter
An ammeter is connected in series to measure current. A voltmeter is connected in parallel to measure voltage.
easy - 15
Earthquakes are recorded with a:
Correct answer: D. Seismograph
A seismograph records ground vibrations. Earthquake magnitude is reported on scales such as the moment magnitude scale.
easy - 16
The loudness of sound is commonly measured in:
Correct answer: D. Decibels
Sound level is measured in decibels (dB). Long exposure to sound above about 85 dB can damage hearing.
easy - 17
The speed of sound in air at about 20 °C is approximately:
Correct answer: C. 343 m/s
Sound travels at about 343 m/s in air at room temperature. It is much faster in water (about 1,500 m/s) and in solids.
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Sound cannot travel through:
Correct answer: B. A vacuum
Sound is a mechanical wave and needs a medium. In a vacuum there are no particles to vibrate, so sound cannot travel.
easy - 19
The splitting of white light into its seven colours by a prism is called:
Correct answer: D. Dispersion
Different colours bend by different amounts when they pass through a prism, which spreads white light into a spectrum.
easy - 20
Which type of mirror is used as a rear-view mirror in vehicles?
Correct answer: A. Convex mirror
A convex mirror gives a wider field of view, though objects appear smaller and farther away than they really are.
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