### Correct Option: A. To increase the voltage while decreasing the current #### Detailed Explanation: A transformer is an electrical device that operates on the principle of electromagnetic induction to transfer electrical energy between two or more circuits. Its primary function is to change the voltage level of alternating current (AC) while maintaining the power (minus losses due to inefficiency). 1. **How Transformers Work**: - A transformer consists of two coils of wire, known as the primary coil and the secondary coil, wound around a magnetic core. - When an alternating current flows through the primary coil, it creates a changing magnetic field around it. - This changing magnetic field induces a voltage in the secondary coil through electromagnetic induction. - The ratio of the number of turns in the primary coil (N₁) to the number of turns in the secondary coil (N₂) determines whether the transformer increases or decreases voltage. 2. **Voltage and Current Relationship**: - The relationship between the primary voltage (V₁), secondary voltage (V₂), primary current (I₁), and secondary current (I₂) can be described by the following equations: - \( \frac{V₂}{V₁} = \frac{N₂}{N₁} \) (Voltage Ratio) - \( \frac{I₂}{I₁} = \frac{N₁}{N₂} \) (Current Ratio) - From these equations, if the transformer increases the voltage (V₂ > V₁), the current in the secondary coil will decrease (I₂ < I₁), and vice versa. This is a direct consequence of the conservation of energy, where the power input (P₁ = V₁ * I₁) equals the power output (P₂ = V₂ * I₂) in an ideal transformer (ignoring losses). 3. **Applications**: - Transformers are widely used in power distribution systems to step up voltage for efficient long-distance transmission and then step down voltage for safe use in homes and businesses. #### Why Other Options Are Incorrect: - **Option B: To store electrical energy for later use**: - This option is incorrect because transformers do not store energy; they merely transfer energy from one circuit to another. Devices that store electrical energy include capacitors and batteries. - **Option C: To convert alternating current (AC) to direct current (DC)**: - This option is also incorrect. Transformers only work with AC. To convert AC to DC, a rectifier is used, which is a different type of device that allows current to flow in one direction only. - **Option D: To measure the resistance in the circuit**: - This option is incorrect as well. Transformers do not measure resistance; they are used to change voltage levels. Measuring resistance is typically done with an ohmmeter or multimeter. ### Summary of Key Points: - A transformer increases or decreases voltage while conserving power in AC circuits. - The voltage and current relationship is governed by the turns ratio of the coils. - Transformers are essential for efficient power transmission and distribution. - They do not store energy, convert AC to DC, or measure resistance. This understanding of transformers is crucial for anyone studying electrical engineering or physics, as it lays the foundation for more advanced concepts in electrical systems.