AP Physics C Questions on EMF and Terminal Voltage with Solutions

📚 Quick Study Guide

• ⚡ Electromotive Force (EMF, $\mathcal{E}$): The EMF is the voltage generated by a battery or generator. It's the total potential difference across the source when no current is flowing. Think of it as the 'ideal' voltage.
• 🔋 Terminal Voltage (V): The actual voltage available at the terminals of a battery when current is flowing. It's always less than or equal to the EMF due to internal resistance (r).
• 📉 Internal Resistance (r): Every real battery has internal resistance, which causes a voltage drop when current flows.
• 📐 Relationship: The relationship between EMF, terminal voltage, current (I), and internal resistance is given by: $V = \mathcal{E} - Ir$.
• 💡 Power Dissipation: The power dissipated by the internal resistance is $P = I^2r$.
• 🔑 Key Concepts: EMF is the cause, voltage is the effect. Internal resistance reduces the terminal voltage.

🧪 Practice Quiz

1. What does EMF stand for?
   1. (A) Electrical Magnetic Field
   2. (B) Electromotive Force
   3. (C) Energy Magnetic Flux
   4. (D) Electromagnetic Frequency
2. A battery has an EMF of 12 V and an internal resistance of 0.5 $\Omega$. What is the terminal voltage when a current of 2 A is flowing through it?
   1. (A) 10 V
   2. (B) 11 V
   3. (C) 13 V
   4. (D) 24 V
3. Which of the following factors affects the terminal voltage of a battery?
   1. (A) EMF only
   2. (B) Internal resistance only
   3. (C) Current only
   4. (D) EMF, internal resistance, and current
4. What happens to the terminal voltage as the current drawn from the battery increases?
   1. (A) It increases
   2. (B) It decreases
   3. (C) It remains constant
   4. (D) It oscillates
5. A battery with an EMF of 9 V has a terminal voltage of 8.5 V when delivering a current of 1 A. What is its internal resistance?
   1. (A) 0.25 $\Omega$
   2. (B) 0.5 $\Omega$
   3. (C) 1.0 $\Omega$
   4. (D) 1.5 $\Omega$
6. The internal resistance of a battery is due to:
   1. (A) The external circuit
   2. (B) The chemical reactions within the battery
   3. (C) The size of the battery
   4. (D) The EMF of the battery
7. If the internal resistance of a battery is zero, what is the relationship between the EMF and terminal voltage?
   1. (A) Terminal voltage is always greater than EMF
   2. (B) Terminal voltage is always less than EMF
   3. (C) Terminal voltage is equal to EMF
   4. (D) There is no relationship