14.1 Electric Current
SLO 14.1.1 — Define electric current
✅ Definition (Complete Concept)
Electric current is the rate of flow of electric charge through a conductor.
Where:
I = current (ampere)
Q = charge (coulomb)
t = time (second)
✅ SI Unit
Ampere (A)
1 A = 1 coulomb per second.
✅ Deep Concept
• Current is not the amount of charge — it is the rate of charge flow.
• If 10 C flows in 2 s → Current = 5 A
• If same 10 C flows in 10 s → Current = 1 A
So slower charge flow = smaller current.
✅ Microscopic View (Very Important for Conceptual MCQs)
In metals:
• Free electrons move randomly.
• When potential difference is applied → electrons drift in one direction.
• This slow movement is called drift velocity.
,Important:
Drift velocity is very slow, but current appears instantly because electric field spreads quickly.
⚠ AKU-EB Concept Trap
If:
Charge increases but time increases more → current decreases.
Large conductor does NOT mean more current automatically.
Current depends on applied potential difference AND resistance.
SLO 14.1.2 — Differentiate between conventional and non-
conventional (electronic) current
✅ Conventional Current
• Assumed direction of current from positive to negative terminal.
• Historically defined before discovery of electrons.
✅ Electronic Current
• Actual movement of electrons.
• Direction is from negative to positive terminal.
✅ Key Concept
Conventional current direction is opposite to electron flow.
In circuit diagrams → we use conventional current.
⚠ Conceptual MCQ Trap
If electrons move left → conventional current moves right.
,14.2 Potential Difference and Electromotive
Force (e.m.f.)
SLO 14.2.1 — Differentiate between potential difference and
electromotive force
✅ Potential Difference (V)
Definition:
Work done per unit charge between two points in a circuit.
It is the energy used by components. ✅ Electromotive Force (E.M.F.)
Definition:
Energy supplied per unit charge by a source (battery).
✅ Conceptual Difference
Potential Difference EMF
Energy used Energy supplied
Across resistor Across battery Terminals
Measured when current flows Measured when no current flows
Terminal voltage Open circuit voltage
⚠ Very Important Concept
When circuit is closed:
Terminal voltage < EMF
Because some energy is lost inside battery (internal resistance).
, AKU-EB loves this concept.
SLO 14.2.2 — Investigate the potential difference across
circuit components and mention its SI unit
✅ SI Unit
Volt (V)
1 Volt = 1 Joule per Coulomb
✅ Series Circuit Concept
• Total voltage = sum of individual voltages
✅ Parallel Circuit Concept
• Voltage same across all branches
V1=V2=V3
⚠ MCQ Trap
If one bulb removed in parallel:
Other bulbs still get full voltage.
If one bulb removed in series:
Entire circuit stops.
SLO 14.1.1 — Define electric current
✅ Definition (Complete Concept)
Electric current is the rate of flow of electric charge through a conductor.
Where:
I = current (ampere)
Q = charge (coulomb)
t = time (second)
✅ SI Unit
Ampere (A)
1 A = 1 coulomb per second.
✅ Deep Concept
• Current is not the amount of charge — it is the rate of charge flow.
• If 10 C flows in 2 s → Current = 5 A
• If same 10 C flows in 10 s → Current = 1 A
So slower charge flow = smaller current.
✅ Microscopic View (Very Important for Conceptual MCQs)
In metals:
• Free electrons move randomly.
• When potential difference is applied → electrons drift in one direction.
• This slow movement is called drift velocity.
,Important:
Drift velocity is very slow, but current appears instantly because electric field spreads quickly.
⚠ AKU-EB Concept Trap
If:
Charge increases but time increases more → current decreases.
Large conductor does NOT mean more current automatically.
Current depends on applied potential difference AND resistance.
SLO 14.1.2 — Differentiate between conventional and non-
conventional (electronic) current
✅ Conventional Current
• Assumed direction of current from positive to negative terminal.
• Historically defined before discovery of electrons.
✅ Electronic Current
• Actual movement of electrons.
• Direction is from negative to positive terminal.
✅ Key Concept
Conventional current direction is opposite to electron flow.
In circuit diagrams → we use conventional current.
⚠ Conceptual MCQ Trap
If electrons move left → conventional current moves right.
,14.2 Potential Difference and Electromotive
Force (e.m.f.)
SLO 14.2.1 — Differentiate between potential difference and
electromotive force
✅ Potential Difference (V)
Definition:
Work done per unit charge between two points in a circuit.
It is the energy used by components. ✅ Electromotive Force (E.M.F.)
Definition:
Energy supplied per unit charge by a source (battery).
✅ Conceptual Difference
Potential Difference EMF
Energy used Energy supplied
Across resistor Across battery Terminals
Measured when current flows Measured when no current flows
Terminal voltage Open circuit voltage
⚠ Very Important Concept
When circuit is closed:
Terminal voltage < EMF
Because some energy is lost inside battery (internal resistance).
, AKU-EB loves this concept.
SLO 14.2.2 — Investigate the potential difference across
circuit components and mention its SI unit
✅ SI Unit
Volt (V)
1 Volt = 1 Joule per Coulomb
✅ Series Circuit Concept
• Total voltage = sum of individual voltages
✅ Parallel Circuit Concept
• Voltage same across all branches
V1=V2=V3
⚠ MCQ Trap
If one bulb removed in parallel:
Other bulbs still get full voltage.
If one bulb removed in series:
Entire circuit stops.
