⚡ Electrical Quantities – Units and Dimensions Table
The following table lists important electrical and magnetic quantities along with their SI units and dimensional formulas. This is useful for students preparing for SSC JE, RRB JE, GATE EE, UPPCL JE, and other technical competitive exams.
| S. No. | Quantity | Symbol | SI Unit | Dimensional Formula |
|---|---|---|---|---|
| 1 | Electric Current | I | Ampere (A) | A |
| 2 | Electric Charge | Q | Coulomb (C) | A·T |
| 3 | Voltage (Electric Potential) | V | Volt (V) | M L² T⁻³ A⁻¹ |
| 4 | Resistance | R | Ohm (Ω) | M L² T⁻³ A⁻² |
| 5 | Conductance | G | Siemens (S) | M⁻¹ L⁻² T³ A² |
| 6 | Capacitance | C | Farad (F) | M⁻¹ L⁻² T⁴ A² |
| 7 | Inductance | L | Henry (H) | M L² T⁻² A⁻² |
| 8 | Power | P | Watt (W) | M L² T⁻³ |
| 9 | Energy / Work Done | W / E | Joule (J) | M L² T⁻² |
| 10 | Electric Field Intensity | E | V/m | M L T⁻³ A⁻¹ |
| 11 | Electric Flux | Φₑ | Coulomb (C) | A·T |
| 12 | Electric Flux Density | D | C/m² | A·T·L⁻² |
| 13 | Permittivity | ε | F/m | M⁻¹ L⁻³ T⁴ A² |
| 14 | Magnetic Field Strength | H | A/m | A·L⁻¹ |
| 15 | Magnetic Flux | Φ | Weber (Wb) | M L² T⁻² A⁻¹ |
| 16 | Magnetic Flux Density | B | Tesla (T) | M T⁻² A⁻¹ |
| 17 | Permeability | μ | H/m | M L T⁻² A⁻² |
| 18 | Reluctance | ℜ | At/Wb | M⁻¹ L⁻² T² A² |
| 19 | Permeance | Λ | Wb/At | M L² T⁻² A⁻² |
| 20 | Magnetomotive Force (MMF) | Fₘ | Ampere-turn (At) | A |
| 21 | Magnetic Field Intensity | H | A/m | A·L⁻¹ |
| 22 | Magnetic Reluctivity | ν | 1/H·m | M⁻¹ L⁻¹ T² A² |
| 23 | Reactance | X | Ohm (Ω) | M L² T⁻³ A⁻² |
| 24 | Impedance | Z | Ohm (Ω) | M L² T⁻³ A⁻² |
| 25 | Admittance | Y | Siemens (S) | M⁻¹ L⁻² T³ A² |
| 26 | Susceptance | B | Siemens (S) | M⁻¹ L⁻² T³ A² |
| 27 | Conductivity | σ | S/m | M⁻¹ L⁻³ T³ A² |
| 28 | Resistivity | ρ | Ω·m | M L³ T⁻³ A⁻² |
Below are the important multiple-choice questions (MCQs) based on Units and Dimensions of commonly used electrical quantities like voltage, current, resistance, capacitance, inductance, flux, etc., helpful for SSC JE, RRB JE, UPPCL JE, GATE EE, and other technical exams.
1. The SI unit of electric current is:
- a) Coulomb
- b) Volt
- c) Ampere
- d) Ohm
Explanation: Electric current is the rate of flow of charge. Its SI unit is Ampere (A).
2. The dimensional formula of voltage (V) is:
- a) M L² T⁻³ A⁻¹
- b) M L² T⁻²
- c) M L T⁻²
- d) M L⁰ T⁻² A⁻¹
Explanation: Voltage = Work done / Charge = (M L² T⁻²) / (A T) = M L² T⁻³ A⁻¹
3. The unit of power factor is:
- a) Watt
- b) Unitless
- c) Volt-Ampere
- d) Hertz
Explanation: Power factor = Cos(ϕ), a pure ratio without units. So it is dimensionless.
4. Which of the following has unit of Henry (H)?
- a) Capacitance
- b) Resistance
- c) Inductance
- d) Conductance
Explanation: The SI unit of inductance is Henry (H).
5. The dimensional formula of electric power is:
- a) M L² T⁻³
- b) M L² T⁻²
- c) M L² T⁻¹
- d) M L² T⁻⁴
Explanation: Power = Energy / Time = (M L² T⁻²) / T = M L² T⁻³
6. What is the unit of electric flux (Φ)?
- a) Ampere-meter
- b) Volt-meter
- c) Coulomb
- d) Tesla
Explanation: Electric flux = ∫E·dA. Unit = N·m²/C = Coulomb
7. Magnetic flux has the unit:
- a) Weber
- b) Tesla
- c) Henry
- d) Ampere
Explanation: Magnetic flux (Φ) = B × A. Unit = Tesla × m² = Weber (Wb)
8. What is the unit of magnetic flux density (B)?
- a) Henry/m
- b) Ampere/m
- c) Weber/m²
- d) Coulomb/m²
Explanation: B = Φ / A ⇒ Unit = Weber/m² = Tesla
9. The dimensional formula of resistance is:
- a) M L² T⁻³ A⁻²
- b) M L² T⁻²
- c) M L² T⁻⁴
- d) M L² T⁻³ A⁻¹
Explanation: Resistance = Voltage / Current = (M L² T⁻³ A⁻¹) / A = M L² T⁻³ A⁻²
10. Unit of magnetic field intensity (H) is:
- a) A/m
- b) Tesla
- c) Weber
- d) Wb/m²
Explanation: H = Magnetizing force ⇒ Unit = Ampere/meter
11. MMF (Magneto Motive Force) unit is:
- a) Tesla
- b) Ampere-turns
- c) A/m
- d) Weber
Explanation: MMF = N × I, unit = Ampere-turns (At)
12. The SI unit of permittivity (ε) is:
- a) F/m
- b) H/m
- c) C/V
- d) C/m
Explanation: Permittivity ε = C / V·m ⇒ SI unit = Farad per meter
13. What is the dimensional formula of capacitance?
- a) M⁻¹ L⁻² T⁴ A²
- b) M⁻² L⁻² T⁴
- c) M⁻¹ L² T³ A⁻²
- d) M L² T⁻² A⁻²
Explanation: Capacitance = Q / V = (A·T) / (M L² T⁻³ A⁻¹) = M⁻¹ L⁻² T⁴ A²
14. The unit of reluctance is:
- a) Henry
- b) At/Wb
- c) Tesla
- d) A/m
Explanation: Reluctance = MMF / Flux = Ampere-turns / Weber = At/Wb