How is the electricity that flows from household outlets produced? Learn about electromagnetic induction, the mechanism that generates electricity.
Basic Knowledge
Electromagnetic induction is the phenomenon in which a changing magnetic field inside a coil causes current to flow in the coil. It was discovered by Faraday in 1831.
The current produced at this time is called induced current, and the voltage is called induced electromotive force. The current flows in a direction that opposes the change in the magnetic field (Lenz’s law).
Ways to increase induced current:
① Move the magnet quickly
② Use a strong magnet
③ Increase the number of turns in the coil
Conversely, if the magnet and coil do not move, no current flows. The key is change.
Electromagnetic induction (the phenomenon in which a change in a magnetic field produces current. Discovered by Faraday)
Induced current (current produced by electromagnetic induction)
Lenz’s law (induced current flows in a direction that opposes the change in the magnetic field)
Direct current (DC) (current flowing in a constant direction. Current produced by a dry cell)
Alternating current (AC) (current whose direction changes periodically. Household outlets)
Generator (a machine that produces electricity through electromagnetic induction)
Further Exploration (Background and Significance)
A generator is a machine that uses electromagnetic induction. It continuously produces current by rotating a coil in a magnetic field. Thermal, hydroelectric, nuclear, wind, and geothermal power generation all ultimately use a turbine to drive a generator.
Household outlets provide alternating current (AC). In Japan:
・Eastern Japan: 50Hz (the direction changes 50 times per second)
・Western Japan: 60Hz (the direction changes 60 times per second)
This difference remains from the machinery imported during the Meiji era.
AC was chosen because a transformer can easily change its voltage. At power plants, the voltage is increased to several hundred thousand V for transmission, then gradually reduced at substations before reaching homes at 100V. This reduces transmission loss ( I²R ).
Electric vehicles and solar power generation produce direct current (DC), so an inverter changes it into AC for household use.
- Electromagnetic induction: current is produced by a change in a magnetic field
- Discovered by Faraday in 1831
- To increase induced current: move the magnet faster, use a stronger magnet, and increase the number of turns
- Lenz’s law: current flows in a direction that opposes the change
- Direct current (DC): dry cells and batteries
- Alternating current (AC): outlets. Eastern Japan 50Hz, Western Japan 60Hz
- A transformer can change the voltage of AC
Points to Note (Easily Confused)
① Electromagnetic induction occurs only when the magnetic field changes. When the magnet stops, the current also becomes zero. ② Distinguish between direct current and alternating current. Household electricity is AC; batteries produce DC. ③ Japan’s AC frequencies are 50Hz in the east and 60Hz in the west. This often appears on tests. ④ Generators and motors have an opposite relationship. A generator changes rotation into electricity; a motor changes electricity into rotation.
Practice
- Who discovered electromagnetic induction?
- What is the frequency of AC in eastern Japan?
- Give one way to increase induced current.