Units and Dimensional Formula MCQ Quiz - Objective Question with Answer for Units and Dimensional Formula - Download Free PDF

• The SI unit of angular frequency is rad/sec.
• It refers to the angular displacement of an object per unit time and is given by:

          \(\omega = \nu × 2\pi\)

          where, \(\nu\) is the frequency.

The correct answer is Henry.

• Henry is the SI unit of mutual inductance.

Key Points

• Mutual Inductance is the interaction of one coil's magnetic field on another coil as it induces a voltage in the adjacent coil.
• It is the basic operating principle of the transformer, motors, generators, and many other electrical components that interact with another magnetic field. 
• The mutual inductance between the two coils can be greatly increased by positioning them on a common soft iron core or by increasing the number of turns.

Additional Information

• Weber is the SI unit of magnetic flux.
• Farad is the SI unit of electrical capacitance.
• Tesla (T) is SI unit of magnetic flux density or magnetic field strength.

The correct answer is option 2 i.e. ms-2.

Key Points

• Earth pulls an object towards its center. The acceleration generated due to this force is called gravity acceleration (g).
• In SI units this acceleration is measured in meters per second squared (m/s²).
• The acceleration due to the gravity of the earth is referred to as 'g'.
• The approximate value of the acceleration due to the gravity of the earth is 9.8 m/s2.
• The weight of an object on the Earth's surface is the downwards force on that object.
• It was explained by Newton's second law of motion or F = ma.

The correct answer is Fermi.

Key Points

• Fermi is a unit of length used to measure nuclear distances, = 10⁻¹⁵ meters. Hence option 2 is correct.
• It is named for the Italian physicist Enrico Fermi (1901–1954).
• A fermi is equivalent to a femtometer and is the older non–SI measurement unit of length.
• Femtometer is a derived metric measurement unit of length.
• Since it is a typical length-scale, and often referenced in nuclear physics. 

Additional Information

• Angstrom is the unit of length used to measure the wavelength of light, 1 Å = 10^-10 m.
• A light-year is the unit of length for measuring astronomical distances.
• Light year = distance traveled by light in 1 year = 9.4605 × 10¹⁵ m.
• Astronomical unit = Mean distance between the sun and earth = 1.5 × 10¹¹ m.
• Parsec = 3.26 light years = 3.084×10¹⁶ m.
• The barn is the unit of area for measuring scattering cross-section of collisions. 1 barn = 10^-28 m².
• Chronometers and metronomes are time-measuring instruments. The quantity having the same unit in all the systems of units is time.

The correct answer is Dyne.

Key Points

• CGS System
  • In this system, the units of length, mass, and time are centimeter, gram, and second respectively.
  • It is also called Gaussian System.
• Force
  • Any action which causes pull or push on a body is called force.
  • It is a vector quantity.
  • Its SI unit is Newton and the CGS unit is Dyne.
  • 1 newton= 10⁵dyne.

Additional Information

• Watt
  • It is a SI unit of Power.
  • Power is the time rate of work done by a body.
  • Power is a scalar quantity.
  • Power= Work/Time
• Erg
  • It is a CGS unit of Work.
  • When a body is displaced by applying force on it, then work is said to be done.
  • Its SI unit is Newton-meter or Joule
  • It is a scalar quantity.
  • 1 joule= 10⁷erg

The correct answer is 10-4 microns.

Key Points

Read the question ,it is asking value  in microns not meter.

If asked in meters then the value will be 1 Angstroms  = 10^-10 m.

But asked in microns

• 1 mm = 10^-3 m
• 1 micron = 10^-3 mm
  • ⇒ 1 micron = 10-6 m
• 1 Angstrom = 10^-10 m
  • 1 Angstrom = 10-10 m = 10-10 × 106 micron = 10-4 micron.

Confusion Points

1 Angstrom = 10^-10 meter

1 Angstrom =  10^-4 micron

Additional Information

• An Angstrom is a unit of length used to measure very small distances.
• 1 Angstroms to = 0.0001 Microns 
• It is named after Anders Jonas Ångström (Swedish physicist).
• A micron is one-millionth of a meter (10−6 m) and one Angstrom is 10-4 micron.

The correct answer is Ohm.

Key Points

• Impedance is the total sum of resistance and reactance.
• The SI Unit of Impedance(Z), resistance(R), and reactance(X) is Ohm(Ω).
• Reactance is a kind of imaginary resistance offered by electrical components like Capacitance and Inductor.
  • Reactance offered by the Inductor is called Inductive reactance, given as X_L = 2πfL.
  • Reactance offered by the Capacitor is called Capacitor reactance, given as  \(X_{C}=\frac{1}{2\pi fC}\).
  • Where 'f' - frequency of the source, 'L' - Inductance, and 'C' - Capacitance.

Additional Information 

Concept:

Power: The rate of work done by the electric energy is called power. It is denoted by P.

• The SI unit of power is the watt (W).
• Watt is a small unit that's why a kilowatt-hour is used as the unit for electrical energy.

1 unit of electric energy: When a one-kilowatt load works for 1 hour then the energy consumed is called 1 unit of electricity.

• 1 Unit of electricity = 1 kWh = 1000 Watt-hour = 3.6 × 106 J
• 1 Kilo-watt = 1000 Watt

1 Watt: The energy consumption rate of 1 joule per second is called 1 watt.

Explanation:

The correct answer is energy.

• The capacity to do work or power consumed in a given time is called energy.
• Power is the rate of doing work or the rate at which energy is spent. 
• Kilowatt-hour is the unit of energy. 

Key Points

• One thousand-watt makes one kilowatt.
• 1 kw hour is equal to 3600 kilojoules.
• For billing units of energy delivered to consumers by electric appliances, this unit is used.
• It is a non-SI metric unit system.
• The one kilowatt of hour sustained for one hour is the composite unit of energy.
• In kilowatt-hours, the electrical energy is typically sold to consumers.
• In terawatt hours, the major energy production or consumption is expressed.
• How much energy is used by us is measured by Kilowatt-hour.

Mistake Points

Energy is the total amount of work done, and power is how fast you can do it. In other words, power is energy per unit of time. Power is watts. Energy is watt-hours.

The correct answer is Columb.

Key Points

• A Coulomb is defined as the amount of electric charge transported by one ampere current in one second from one point to another..
• Columb is used to measure the amount of Electric charge.  
• Electric charge: 
  • Electric charge is a general property of protons, electrons, and subatomic particles.
  • Protons are positively charged while electrons are negatively charged.
  • Similar charges repel each other whereas opposite charges attract each other.

Additional Information

• ​Luminous intensity:
  • Luminous intensity is calculated the weighted power of wavelength, transit by a source of light in any specific direction per unit solid angle.
  • It depends on the luminosity function, a standardized phenomenon of the sensitivity of the human eye.
  • The SI unit of luminous intensity is Candela.
• Volt: 
  • Volt(V) is the unit of Electric voltage or electric potential difference.
  • One Volt is described as the consumption of energy of one joule per electric charge of one coulomb.

The correct answer is Joule.

• Heat is the energy that is transferred from one body to another as the result of a difference in temperature.
• The S.I unit of heat is Joule.
• One joule equals the work done (or energy expended) by a force of one newton acting over a distance of one meter.

Additional Information

• A calorie is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius.
• A kilocalorie is equal to one thousand calories.
• The erg is equal to 10⁻⁷ joules. It is the unit of energy or work in the cgs system.

Mistake Points

• The unit of heat is joule (J) in SI unit system and calorie is used in BTU system of units. 

The correct answer is " Femto"

Important Points

SI prefixes and symbols:

The correct answer is Kg·m/s2.

Key Points

• The pressure is the perpendicular force acting per unit area.
• SI unit of pressure is Pascal, which is equivalent to 1 N force acting per sq. meter.
• It is given by, P = \(F\over A\)

Additional Information

• Its unit can also be derived from the formula as N/m².
• Kg·m/s2 is the derived unit of force.
• \(1 Pascal = {F \over A} \) \(= {ma \over A} \)\(= {Kg{m/s^{2}} \over m^{2}} \) = Kg/(m·s2).

Important Points

• Both pressure and stress are given by the same formula i.e. \(F\over A\).
• The main difference between them is the angle at which the force is applied to a body.
• When the force applied to a body is perpendicular to the area, it is called pressure.
• If the angle is other than 90°, then it is called stress.

Mistake Points

• Kg·m/s2 is the SI unit of force and not of pressure.
• The question asked is about the one which cannot be the unit, since options 2 and 3 are very close, so answer the question patiently.

The correct answer is 66.67.

Key Points

The correct answer is Lens.

• The power of the lens is expressed in terms of Dioptre.
• The power of the lens is defined as the ability of the lens to converge or diverge the ray of light passing through it.
• The power of the convex lens is said to be more if the ray of the light converges more strongly towards the optical centre. 
• It depends on the focal length of the lens.
• It is defined as the reciprocal of the focal length in meters. 
• \(Power = {1\over f}\)
• The SI unit of power of the lens is diopter and is denoted by D.
• One diopter is defined as the power of the lens that has a focal length of one meter.
• The focal length of the convex lens is positive so the power is positive and that of the concave lens is negative as its focal length is negative.

The correct answer is Volt.

• Volt is the S.I. unit of electric potential difference.
• The coulomb is an SI unit of electric charge. 
• A joule is a derived unit of energy.
• Ampere is the SI unit of current.

​Important Points

• A voltmeter is always connected in parallel.
• An Ammeter is connected in series.
• A galvanometer is used for detecting and indicating electric current.
• 1 coulomb is equal to 6.24 × 10¹⁸ electrons.