AP Physics 2 Questions on Transformers and Electromagnetic Induction

📚 Quick Study Guide

• 🧲 Electromagnetic Induction: The production of an electromotive force (EMF) across an electrical conductor in a changing magnetic field.
• 🔄 Faraday's Law: The induced EMF in any closed circuit is equal to the negative of the time rate of change of the magnetic flux through the circuit. Mathematically, $\mathcal{E} = -N \frac{d\Phi_B}{dt}$, where $\mathcal{E}$ is the EMF, $N$ is the number of turns in the coil, and $\Phi_B$ is the magnetic flux.
• 🧭 Lenz's Law: The direction of the induced EMF is such that it opposes the change in magnetic flux that produced it.
• ⚙️ Transformers: Devices used to increase or decrease AC voltage. They consist of two or more coils electrically isolated but magnetically linked.
• ➗ Transformer Equation: $\frac{V_p}{V_s} = \frac{N_p}{N_s}$, where $V_p$ is the primary voltage, $V_s$ is the secondary voltage, $N_p$ is the number of primary turns, and $N_s$ is the number of secondary turns.
• ⚡ Power in Transformers: In an ideal transformer (no energy loss), power in equals power out: $P_{in} = P_{out}$, so $V_p I_p = V_s I_s$.
• 📉 Step-Up Transformer: Increases voltage ($V_s > V_p$ and $N_s > N_p$).
• 📈 Step-Down Transformer: Decreases voltage ($V_s < V_p$ and $N_s < N_p$).

🧪 Practice Quiz

1. Which of the following statements best describes Faraday's Law of electromagnetic induction?
   1. A) The induced EMF is directly proportional to the rate of change of electric flux.
   2. B) The induced EMF is inversely proportional to the rate of change of magnetic flux.
   3. C) The induced EMF is equal to the negative of the time rate of change of magnetic flux.
   4. D) The induced EMF is independent of the magnetic flux.
2. A transformer has 500 turns on its primary coil and 100 turns on its secondary coil. If the primary voltage is 120 V, what is the secondary voltage, assuming an ideal transformer?
   1. A) 24 V
   2. B) 600 V
   3. C) 12 V
   4. D) 30 V
3. Lenz's Law is a consequence of which conservation law?
   1. A) Conservation of Charge
   2. B) Conservation of Momentum
   3. C) Conservation of Energy
   4. D) Conservation of Mass
4. In a step-up transformer, which of the following is true?
   1. A) The number of turns in the primary coil is greater than the number of turns in the secondary coil.
   2. B) The primary voltage is greater than the secondary voltage.
   3. C) The secondary voltage is greater than the primary voltage.
   4. D) The primary and secondary voltages are equal.
5. What is the purpose of laminating the core of a transformer?
   1. A) To increase the magnetic flux.
   2. B) To reduce eddy current losses.
   3. C) To increase the resistance of the core.
   4. D) To decrease the inductance of the coils.
6. A coil with 200 turns is placed in a magnetic field. If the magnetic flux through the coil changes from 0.2 Wb to 0.6 Wb in 0.5 seconds, what is the magnitude of the induced EMF?
   1. A) 40 V
   2. B) 80 V
   3. C) 160 V
   4. D) 320 V
7. If the primary current in an ideal transformer is 2 A and the secondary current is 10 A, what is the ratio of the number of turns in the primary coil to the number of turns in the secondary coil ($N_p/N_s$)?
   1. A) 1/5
   2. B) 5
   3. C) 1/25
   4. D) 25