5.4 Electromotive force and internal resistance

• Electromotive force (EMF) is the potential difference that a source of electrical energy can provide when there is no current flowing
• Match the property with its definition:

  EMF (ε) ↔️ The maximum potential difference the source can provide

  Terminal Potential Difference (V) ↔️ The actual potential difference across the terminals when current is flowing

  Internal Resistance (r) ↔️ The resistance within the source that causes a voltage drop
• EMF is measured with no current flowing
• EMF represents the maximum voltage a source can provide, while PD is the actual voltage across the terminals when current flows.

  True
• Internal resistance reduces the terminal potential difference below the EMF
• Under what condition is potential difference measured?

  Current flowing
• Internal resistance within a battery causes a voltage drop
• The internal resistance of a battery reduces the terminal potential difference below the EMF
• Higher temperatures generally decrease the internal resistance of a battery.


  True
• The terminal potential difference is the actual voltage across a battery's terminals when current is flowing.
• The EMF is measured when no current is flowing in the circuit.

  True
• Match the term in the EMF equation with its definition:

  V ↔️ Terminal potential difference

  ε ↔️ Electromotive force

  I ↔️ Current

  r ↔️ Internal resistance
• What is the formula that relates EMF, terminal potential difference, current, and internal resistance?

  $V =$$\varepsilon - Ir$
• The terminal potential difference is the EMF minus the voltage drop across the internal resistance.


  True
• Electromotive force is the potential difference when no current is flowing.
• Match the property with its description:

  EMF ↔️ Maximum potential difference when no current flows

  PD ↔️ Voltage across terminals when current flows

  Internal Resistance ↔️ Resistance within the source causing voltage drop
• Order the factors affecting internal resistance:

  1️⃣ Battery Age

  2️⃣ Temperature

  3️⃣ Battery Composition

  4️⃣ Discharge Rate
• What is the power output of a 12V battery with 0.5Ω internal resistance supplying 2A of current?

  22W
• If a battery has an EMF of 12V, internal resistance of 0.5Ω, and a current of 2A, the terminal potential difference is 11V.


  True
• The terminal potential difference is equal to the EMF when no current is flowing.

  False
• Match the property with its description:

  EMF ↔️ Maximum voltage when no current flows

  Terminal Potential Difference ↔️ Actual voltage during current flow
• The EMF equation relates the terminal potential difference, EMF, current, and internal
• What are the units of terminal potential difference?

  Volts
• The EMF equation can only be used when current is flowing in the circuit.


  True
• What is the terminal potential difference if the EMF is 12V, internal resistance is 0.5Ω, and current is 2A?

  11V
• The terminal potential difference is the same as the EMF when there is no internal resistance.


  True
• What does EMF represent in a source of electrical energy?

  Maximum possible voltage
• The relationship between EMF, terminal potential difference, and internal resistance is described by $V =$$\varepsilon - Ir$.


  True
• What is the formula relating EMF, terminal potential difference, internal resistance, and current?

  $V =$$\varepsilon - Ir$
• When is EMF measured in a circuit?

  No current flowing
• Ordering the factors affecting internal resistance in batteries:

  1️⃣ Battery Age

  2️⃣ Battery Composition

  3️⃣ Discharge Rate

  4️⃣ Temperature
• What happens to internal resistance as a battery ages?

  Increases
• Higher temperatures generally decrease internal resistance.
• Battery age increases internal resistance due to chemical degradation


  True
• Order the steps of how temperature affects internal resistance:

  1️⃣ Higher temperature increases chemical reaction efficiency

  2️⃣ Chemical degradation decreases internal resistance

  3️⃣ Voltage drop is reduced
• The internal resistance of a battery causes a voltage drop that reduces the terminal potential difference.
• Match the property with its correct description for EMF and terminal potential difference:

  EMF (ε) ↔️ Maximum potential difference the source can provide

  Terminal Potential Difference (V) ↔️ Actual voltage when current flows
• The EMF equation relates the terminal potential difference, the electromotive force, the current, and the internal resistance.
• The EMF equation shows that the terminal potential difference is the EMF minus the voltage drop across the internal resistance.


  True
• The EMF equation relates terminal potential difference to current, electromotive force, and internal resistance