5.4 Electromotive force and internal resistance

• What does electromotive force (emf) represent?

  Potential difference when no current flows
• How does internal resistance affect terminal voltage?

  Reduces it
• Emf represents the total energy per unit charge that a source can supply.
• The internal resistance of a power source depends on its material and construction.
• As internal resistance increases, the terminal potential difference decreases.
• Higher temperatures generally decrease the internal resistance of a power source.

  True
• How does internal resistance affect terminal voltage?

  Reduces terminal voltage
• Electromotive force represents the maximum potential difference a power source can provide
• When a battery with an emf of 12V is connected to a resistor, the potential difference across the resistor might be 10V due to internal resistance
• The relationship between emf, terminal voltage, internal resistance, and current is given by ε = V + Ir
• Internal resistance reduces the terminal potential difference
• The relationship between emf, terminal potential difference, internal resistance, and current is expressed as ε = V + Ir
• Which property of a power source affects its internal resistance?

  Material and construction
• The formula relating emf, terminal potential difference, internal resistance, and current is ε = V + Ir
• What happens to the terminal potential difference when internal resistance increases?

  It decreases
• What does higher internal resistance imply for the terminal voltage of a battery?

  Lower terminal voltage
• Internal resistance determines the current flow in a circuit.

  False
• Internal resistance is the resistance within the external circuit.

  False
• The terminal voltage of a power source is affected by its emf, internal resistance, and current.


  True
• Internal resistance reduces the terminal voltage of a power source.


  True
• What does emf represent when no current is flowing?

  Maximum potential difference
• What is internal resistance in a cell or battery?

  Opposition to current flow
• What influences the terminal voltage of a power source?

  Emf, internal resistance, current
• What is the formula relating terminal voltage, emf, internal resistance, and current?

  $V =$$\epsilon - Ir$
• The $I - V$ characteristic of a cell illustrates how current varies with terminal voltage
• The I - V</latex> curve of a real battery is a straight line with a negative slope equal to its internal resistance.

  True
• As current increases, the terminal voltage of a real battery decreases due to the internal resistance.


  True
• How can the emf and internal resistance of a power source be determined using experimental data?

  Measure V at different I
• What is the value of the internal resistance calculated from the given data?

  0.1 Ω
• Determining emf and internal resistance helps understand a power source's performance under load conditions.

  True
• A battery has an emf of 1.5V and a terminal voltage of 1.3V when delivering a current of 0.5A. What is the internal resistance?

  0.4 Ω
• Match the parameter with its description:

  Emf ↔️ Maximum potential difference when no current flows

  Potential Difference ↔️ Voltage across a component when current flows
• What is the terminal voltage of a battery with an emf of 12V, internal resistance of 0.5Ω, and a current of 2A?

  11 V
• What is the terminal voltage of a power source?

  Potential difference across terminals
• What do the I-V characteristics of a power source describe?

  Current-voltage relationship
• The internal resistance of a power source reduces the terminal voltage when current flows
• What are the I-V characteristics of a real power source with non-zero internal resistance?

  Non-linear
• The emf of a battery can be calculated using the equation: \epsilon = V + Ir
• Internal resistance reduces the terminal voltage of a power source when current flows.


  True
• Under what conditions does potential difference occur?

  When the circuit is closed