5.4 Electromotive force and internal resistance

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

  EMF (ε) ↔️ Potential difference with no current flow

  Terminal Potential Difference (V) ↔️ Actual voltage available with current flow

  Internal Resistance (r) ↔️ Resistance within the source
• Temperature is a factor that influences internal resistance.

  True
• The internal resistance of a lead-acid battery is very low
• What is the function of a battery in a simple electrical circuit?

  Provides potential difference
• What does Electromotive Force (EMF) represent when no current is flowing?

  Maximum possible voltage
• The formula relating EMF, terminal potential difference, and internal resistance is V = $\epsilon - Ir$.
• Arrange the factors affecting internal resistance in order of importance:

  1️⃣ Material and construction

  2️⃣ Age of the source

  3️⃣ Temperature
• A simple electrical circuit must include a battery, wires, and a load.


  True
• What is the current flowing in a circuit with an EMF of 12 V, external resistance of 5.5 Ω, and internal resistance of 0.5 Ω?

  2 A
• What is the key difference between EMF and terminal potential difference?

  Current flow
• Electromotive force (EMF) is the maximum potential difference a source can provide when no current is flowing.


  True
• EMF is the actual voltage available at the terminals of a source when current is flowing.

  False
• Match the term with its definition:

  EMF (ε) ↔️ Potential difference with no current flow

  Terminal Potential Difference (V) ↔️ Actual voltage available with current flow

  Internal Resistance (r) ↔️ Resistance within the source
• Internal resistance reduces the terminal potential difference according to the formula $V =$$\epsilon - Ir$, where $I$ is the current
• What is the relationship between voltage, current, and resistance defined by Ohm's Law?

  $V =$$IR$
• What is the function of a battery in a simple electrical circuit?

  Provides voltage
• What does the EMF (ε) of a battery represent?

  Potential difference
• The terminal potential difference (V) is always less than the EMF (ε) due to the voltage drop across the internal resistance.


  True
• A battery with an EMF of $12 V$ and internal resistance of $0.5 \Omega$ supplies a current of $2 A$. What is the terminal potential difference?


  $11 V$
• Match the term with its definition:

  EMF (ε) ↔️ Potential difference with no current flow

  Terminal Potential Difference (V) ↔️ Voltage available with current flow

  Internal Resistance (r) ↔️ Resistance within the source
• Factors affecting internal resistance:

  1️⃣ Material and Construction

  2️⃣ Temperature

  3️⃣ Age
• What formula is used to solve problems involving EMF and internal resistance?

  $V =$$\epsilon - Ir$
• The formula for terminal potential difference (V) is $V =$$\epsilon - Ir$


  True
• What causes the terminal potential difference to be less than the EMF?

  Internal resistance
• Internal resistance reduces the terminal potential difference according to the formula $V =$$\epsilon - Ir$


  True
• What law defines the relationship between voltage, current, and resistance in a circuit?

  Ohm's Law
• The terminal potential difference is always equal to the EMF when internal resistance is present.

  False
• The terminal potential difference (PD) is equal to the EMF when no current is flowing.

  False
• The formula for terminal potential difference (PD) is V = \epsilon - Ir</latex>

  True
• In an example with an EMF of $12 V$, internal resistance of $0.5 \Omega$, and a current of 2 A</latex>, the terminal PD is 11 V
• The internal resistance of a source usually decreases with age due to corrosion.

  False
• Temperature fluctuations can affect the internal resistance of a source and need to be considered in experiments.

  True
• The terminal potential difference is less than the EMF due to internal resistance.


  True
• The formula relating EMF, terminal potential difference, and internal resistance is V = ε - Ir
• Arrange the following sources in order of increasing internal resistance:

  1️⃣ Lead-Acid Battery

  2️⃣ Alkaline Battery

  3️⃣ Lithium Battery
• In a simple electrical circuit, electrons flow from the positive terminal to the negative terminal of the battery.

  False
• Match the electrical term with its definition:

  EMF (ε) ↔️ Potential difference with no current flow

  Terminal Potential Difference (V) ↔️ Actual voltage available with current flow

  Internal Resistance (r) ↔️ Resistance within the source
• The terminal potential difference is always equal to the EMF.

  False
• What is the effect of internal resistance on the terminal potential difference?

  Reduces terminal PD