Units

What is the SI unit of length?
a) Centimeter
b) Foot
c) Meter
d) Inch
✅ c) Meter
Explanation: The metre is the standard SI unit of length, defined by the distance light travels in a vacuum in 1/299,792,458 seconds.

SI unit of time is:
a) Minute
b) Second
c) Hour
d) Day
✅ b) Second
Explanation: The SI unit of time is the second, based on the vibration of cesium atoms.

SI unit of mass is:
a) Pound
b) Gram
c) Tonne
d) Kilogram
✅ d) Kilogram
Explanation: The kilogram is the base unit of mass in the SI system.

SI unit of electric current is:
a) Volt
b) Ampere
c) Watt
d) Ohm
✅ b) Ampere
Explanation: Ampere measures the flow of electric charge per second.

SI unit of temperature is:
a) Celsius
b) Fahrenheit
c) Kelvin
d) Joule
✅ c) Kelvin
Explanation: Kelvin is the absolute temperature scale used in scientific calculations.

SI unit of luminous intensity is:
a) Lumen
b) Watt
c) Candela
d) Lux
✅ c) Candela
Explanation: Candela quantifies the brightness of a light source in a given direction.

SI unit of amount of substance is:
a) Gram
b) Mole
c) Atom
d) Mass
✅ b) Mole
Explanation: A mole represents a specific number (Avogadro's number) of particles.

SI unit of energy is:
a) Calorie
b) Kilowatt
c) Joule
d) Newton
✅ c) Joule
Explanation: A joule is the energy used when a force of one newton moves an object one meter.

SI unit of force is:
a) Dyne
b) Kilogram
c) Newton
d) Pascal
✅ c) Newton
Explanation: Newton is derived as kg·m/s², representing the force needed to accelerate 1 kg by 1 m/s².

SI unit of pressure is:
a) Newton
b) Pascal
c) Joule
d) Calorie
✅ b) Pascal
Explanation: Pascal (Pa) is equal to one newton per square meter (N/m²).

SI unit of power is:
a) Watt
b) Joule
c) Calorie
d) Newton
✅ a) Watt
Explanation: Power is the rate of doing work or transferring energy, and 1 watt = 1 joule/second.

SI unit of work is:
a) Newton
b) Pascal
c) Joule
d) Calorie
✅ c) Joule
Explanation: Work is done when a force moves an object through a distance.

SI unit of charge is:
a) Volt
b) Coulomb
c) Ampere
d) Farad
✅ b) Coulomb
Explanation: 1 Coulomb is the amount of charge transferred by 1 ampere in 1 second.

SI unit of resistance is:
a) Ampere
b) Ohm
c) Volt
d) Watt
✅ b) Ohm
Explanation: Resistance (R) = Voltage (V) / Current (I), and its unit is ohm.

SI unit of potential difference is:
a) Watt
b) Ampere
c) Ohm
d) Volt
✅ d) Volt
Explanation: Volt measures the potential energy per unit charge.

SI unit of frequency is:
a) Hertz
b) Newton
c) Watt
d) Second
✅ a) Hertz
Explanation: Frequency is the number of cycles per second; 1 Hz = 1 cycle/second.

Unit of sound intensity (loudness) is:
a) Watt
b) Hertz
c) Decibel
d) Pascal
✅ c) Decibel
Explanation: Decibel (dB) is a logarithmic unit that measures sound intensity.

Pressure used in weather forecasting is often in:
a) Torr
b) Atmosphere
c) Pascal
d) Bar
✅ b) Atmosphere
Explanation: 1 atm = 101.325 kPa; commonly used in meteorology.

SI unit of heat energy is:
a) Joule
b) Calorie
c) Watt
d) Kelvin
✅ a) Joule
Explanation: Though calorie is also used, SI standard is the joule.

CGS unit of force is:
a) Newton
b) Dyne
c) Joule
d) Calorie
✅ b) Dyne
Explanation: 1 dyne = 10⁻⁵ newton; used in the centimeter-gram-second system.

1 Newton equals:
a) 1 kg·m/s²
b) 1 kg·m/s
c) 1 kg/m²
d) 1 kg/s
✅ a) 1 kg·m/s²
Explanation: Newton’s second law defines force as mass × acceleration.

1 Joule equals:
a) 1 N/m
b) 1 N·m
c) 1 W/s
d) 1 kg·m²
✅ b) 1 N·m
Explanation: Work = Force × distance, measured in Newton-meter (N·m).

Dimensional formula for energy is:
a) [M L² T⁻²]
b) [M L T⁻²]
c) [M T² L⁻²]
d) [L T⁻¹]
✅ a) [M L² T⁻²]
Explanation: Energy = work = force × distance = [M L T⁻²] × [L].

Which quantity is dimensionless?
a) Refractive index
b) Speed
c) Force
d) Work
✅ a) Refractive index
Explanation: It's a ratio (light speeds), so has no units or dimensions.

SI unit of magnetic field strength is:
a) Weber
b) Tesla
c) Gauss
d) Henry
✅ b) Tesla
Explanation: 1 Tesla = 1 weber/m², standard for magnetic flux density.

Unit of acceleration:
a) m/s
b) m/s²
c) km/hr
d) m/hr
✅ b) m/s²
Explanation: Acceleration = change in velocity/time.

SI unit of capacitance is:
a) Farad
b) Coulomb
c) Ampere
d) Tesla
✅ a) Farad
Explanation: Capacitance = charge/voltage.

SI unit of inductance is:
a) Henry
b) Farad
c) Tesla
d) Weber
✅ a) Henry
Explanation: Inductance = flux/current.

SI unit of magnetic flux is:
a) Tesla
b) Weber
c) Volt
d) Farad
✅ b) Weber
Explanation: Magnetic flux = magnetic field × area.

Light year measures:
a) Time
b) Speed
c) Distance
d) Intensity
✅ c) Distance
Explanation: Distance that light travels in one year in a vacuum.

What is 1 Angstrom?
a) 10⁻⁶ m
b) 10⁻¹⁰ m
c) 10⁻⁸ m
d) 10⁻¹² m
✅ b) 10⁻¹⁰ m
Explanation: Used to measure atomic and molecular scales.

Unit of surface tension:
a) N/m
b) N/m²
c) J/kg
d) W/m
✅ a) N/m
Explanation: Force per unit length.

Unit of density:
a) kg/m²
b) kg·m
c) kg/m³
d) kg·s
✅ c) kg/m³
Explanation: Density = mass/volume.

Unit of angular velocity:
a) rad/s
b) m/s²
c) Hz
d) m/s
✅ a) rad/s
Explanation: Angular displacement per unit time.

Lux is the unit of:
a) Luminous intensity
b) Illuminance
c) Light power
d) Brightness
✅ b) Illuminance
Explanation: Illuminance = luminous flux per unit area.

Which unit measures entropy?
a) Joule
b) Joule/Kelvin
c) Watt
d) Newton
✅ b) Joule/Kelvin
Explanation: Entropy = energy per unit temperature.

1 kilowatt-hour equals:
a) 1000 J
b) 3600 J
c) 3.6 × 10⁶ J
d) 360 J
✅ c) 3.6 × 10⁶ J
Explanation: 1 kWh = 1000 W × 3600 s = 3.6 million joules.

Which is a vector quantity?
a) Speed
b) Temperature
c) Displacement
d) Energy
✅ c) Displacement
Explanation: Displacement has both magnitude and direction.

Unit of momentum:
a) kg·m/s
b) kg·m/s²
c) N·m
d) N/s
✅ a) kg·m/s
Explanation: Momentum = mass × velocity.

Unit of power in electric circuits:
a) Watt
b) Ohm
c) Ampere
d) Volt
✅ a) Watt
Explanation: Power = voltage × current.

Unit of work in CGS system is:
a) Erg
b) Joule
c) Dyne
d) Watt
✅ a) Erg
Explanation: 1 erg = 10⁻⁷ joules.

Poise is the unit of:
a) Surface tension
b) Viscosity
c) Acceleration
d) Resistance
✅ b) Viscosity
Explanation: Poise is CGS unit for dynamic viscosity.

Unit of electric field:
a) V/m
b) N/C
c) Both a and b
d) Ohm
✅ c) Both a and b
Explanation: V/m and N/C are equivalent.

Which pair has the same unit?
a) Force and pressure
b) Work and energy
c) Voltage and resistance
d) Frequency and velocity
✅ b) Work and energy
Explanation: Both are measured in joules.

Dimensional formula of pressure:
a) [M L⁻¹ T⁻²]
b) [M L T⁻²]
c) [M L² T⁻²]
d) [M T⁻²]
✅ a) [M L⁻¹ T⁻²]
Explanation: Pressure = force/area = (M L T⁻²) / L²

Refractive index is:
a) Scalar
b) Vector
c) Dimensionless
d) Fundamental
✅ c) Dimensionless
Explanation: It’s a ratio of two similar quantities.

Which unit is NOT fundamental?
a) Kilogram
b) Second
c) Joule
d) Meter
✅ c) Joule
Explanation: Joule is derived (from kg·m²/s²).

1 Pascal =
a) 1 N/m²
b) 1 J/m
c) 1 N·m²
d) 1 kg·m/s
✅ a) 1 N/m²
Explanation: Pascal is pressure unit: force per unit area.

Fundamental quantity with SI unit ‘candela’:
a) Mass
b) Temperature
c) Luminous intensity
d) Area
✅ c) Luminous intensity
Explanation: Candela measures brightness.

Which of these quantities has the unit radian?
a) Angle
b) Speed
c) Acceleration
d) Power
✅ a) Angle
Explanation: Radian is unit of plane angle in SI.