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Explain emf, potential difference and current

Short answer

EMF (E=W/Q) is energy per coulomb supplied by a source. Potential difference (V=W/Q, V=IR) is work per coulomb between two points. Current (I=Q/t) is rate of charge flow. In a circuit I=E/(R+r) and terminal voltage V=E−Ir=IR.

Explain emf, potential difference and current with a circuit diagram.

EMF

Electromotive force (E) is the energy given to each coulomb of charge by a source while moving it round the complete circuit (volt). It is the cause of current. E = W/Q.

Potential difference

Potential difference (V) between two points is the work done in moving one coulomb of charge from one point to the other (volt). V = W/Q. Across a resistor, V = I R.

Current

Current (I) is the rate of flow of charge through a conductor: I = Q/t (ampere). 1 A = 1 C/s. In the external circuit, conventional current flows from the positive terminal of the source to its negative terminal (electrons move the opposite way).

         I ->
   +-------------+
   |             |
 (E,r)          [R]  V = I R
   |             |
   +-------------+

In the circuit: I = E/(R + r), and the terminal voltage V = E − I r = I R. Example: E = 12 V, r = 1 Ω, R = 5 Ω gives I = 2 A, V = 10 V across R, and 2 V is lost inside the source.

✓ Answer checked by Claude Opus 5.5 (high effort)

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