What is the SI unit of current?

Correct — B. The ampere, symbol A, is the SI base unit of electric current.

It is one of the seven SI base units, alongside the metre, kilogram, second, kelvin, mole and candela — which is why current, rather than voltage or resistance, is the electrical quantity treated as fundamental.

One ampere corresponds to one coulomb of charge passing a point each second. Option (b).

Why the others are wrong

• (a)
  Metre — The metre is the SI base unit of length. It is tempting precisely because it does belong to the list of seven base units.
• (c)
  Volt — The volt measures potential difference, the push rather than the flow, and it is a derived unit equal to one joule per coulomb.
• (d)
  Ohm — The ohm measures resistance, the opposition to flow, and is also derived — one volt per ampere, by Ohm's law.

Keep the three electrical quantities apart by what each physically describes.

Current is the rate of flow of charge, measured in amperes. Potential difference is the energy given to each unit of charge, measured in volts. Resistance opposes the flow and is measured in ohms.

Ohm's law ties them together as V = IR. Of the three, only the ampere is an SI base unit; the volt and the ohm are derived from the base units.

Key facts

• The SI base unit of electric current is the ampere, symbol A.
• One ampere corresponds to one coulomb of charge per second.
• The volt is the unit of potential difference and the ohm the unit of resistance.
• The seven SI base units are the metre, kilogram, second, ampere, kelvin, mole and candela.

Common traps

• Choosing volt, because voltage is the electrical quantity named most often in daily life.
• Naming the coulomb, the unit of charge, where the question asks for the rate of flow.

No directly related past PYQ was found.