Understanding EMF, Terminal Voltage, and Internal Resistance

Key Concepts

EMF (Electromotive Force)
- It's a number like 1.5V or 9V written on a battery.
- Represents the energy transferred by the battery per coulomb (not an actual force).
Terminal Voltage
- The actual voltage across the battery terminals when a circuit is in use.
- It can be less than the EMF due to internal resistance causing heat loss.
Internal Resistance
- The inherent resistance within the battery limiting the flow of charge.
- Causes energy to be dissipated as heat.

When a battery is connected to a bulb, it lights up.
Adding more bulbs in parallel makes each bulb dimmer due to increased current draw.
- More current drawn = higher heat loss = lower terminal voltage.

Batteries have electrons (or positive charges for simplicity) which are pushed against electrical repulsion inside the battery, transferring energy to them.
With resistance inside (internal resistance), not all energy transferred to charges becomes useful work (light up a bulb), some is lost as heat.

EMF: Total energy transferred per coulomb by the battery.
Terminal Voltage: Actual energy gained by 1 coulomb after accounting for energy lost as heat.
- Terminal Voltage = EMF - (Heat loss per coulomb)

When there’s more current (moving charges faster), more heat is generated due to internal resistance, reducing terminal voltage.
- Example: Space shuttles heat up more than airplanes due to speed.
If current = 0, terminal voltage ≈ EMF (no heat loss).

Equation: ( V_T = E - I \times R )
- V_T: Terminal Voltage
- E: EMF
- I: Current
- R: Internal Resistance
Terminal voltage is the net energy per coulomb when accounting for internal resistance.

Understanding the relationship between EMF, terminal voltage, and internal resistance explains why devices behave differently under varying current loads.