How a transformers work: • TRANSFORMERS The primary coil is connected to an outside power line. AC (alternating current) in the primary coil creates a changing magnetic field in the primary coil. The changing magnetic field in the primary coil creates a changing magnetic field in the iron core which is connected to the secondary coil. This creates Primary coll N₁ Iron core Secondary coil N₂ V I R a changing magnetic field in the secondary coil. The changing magnetic field in the secondary coil induces a voltage in the secondary coil. The amount Voltage V₁ Magnetic V₁ field lines of voltage depends on the number of loops in the coils. Voltage The secondary coil is connected to the wiring of your device or appliance. Consider a simple transformer that has a 100-turns primary coil and a 1000-turn secondary coil. The primary coil is connected to a 120V AC source and the secondary is connected to an electrical device with a resistance of 1000 ohms. 1. What will be the voltage output of the secondary coil? 2. What current flows in the secondary circuit? Primary voltage (V) V₁- V2 Secondary voltage (V) Turns in primary coil N₁ N₂ Turns in secondary coil I = /R 100 TURNS PHYSICS V. A. (use Ohm's Law) PHYSICS P=IV 1000 TURNS 3. Now that you know the voltage and current, what is the power in the secondary coil? W. 4. Neglecting small heating losses, and knowing that energy is conserved, what is the power in the primary coil? W. 5. Now that you know the power and the voltage across the primary coil, what is the current drawn by the primary coil? A. 6. In England, the standard household voltage is 240V. If you brought your own hair dryer on a trip there, you would need a transformer to step down the voltage before you plug in the appliance. If the transformer steps down voltage from 240V to 120V, and the primary cold has 50 turns, how many turns does the secondary coil have? 7. You are planning a trip to Singapore. Your travel agent fives you the proper transformer to step down the voltage so you can use your electric devise there. Curious, you open the case and find that the primary coil has 46 turns, and the secondary has 24 turns. Assuming the output voltage is 120V, what is the standard household voltage in Singapore? 8. A family from Finland, where the standard household voltage is 220V, is planning a trip to Japan. The transformer they need to use their appliances in Japan has an input coil with 250 turns and an output coil with 550 turns. What is the standard household voltage in Japan? 9. While in Canada, an engineer buys a new electric toothbrush. When she returns home she designs another transformer so she can use the toothbrush in India. This transformer also has an input coil with 240 turns. How many turns should the output coil have?