Electromagnetic Induction In this chapter we will explore; Describe the law of electromagnetic induction and use Lenz’s law to predict the direction of induced current. Describe alternating current (AC) and the operation of an AC generator. Describe how transformers step-up and step-down voltage. Describe how generators, transformers, and the electrical work to provide electricity.

13.1 Electromagnetic Induction In Chapter 12 we learned that an electric current in a conductor can produce a magnetic field. Is the opposite true? Can a magnetic field produce an electric current? In 1831, British physicist Michael Faraday proved that it could. Recall that a constant electric current produces a magnetic field, so it is reasonable to assume that a constant magnetic field produces an electric current…however, it does not. Faraday discovered that the magnetic field must be continuously changing in order to produce an electric current.

13.1 Law of Electromagnetic Induction Electromagnetic Induction is the production of electric current in a conductor moving through a magnetic field. Induction implies that one action causes another action to happen, without direct contact. Faraday brought a permanent magnet near a conductor and induced a current in the conductor. Electric current was produced only when the magnet was moving in the vicinity of the conductor. The Law of Electromagnetic Induction states any change in the magnetic field in the region of a conductor induces a voltage in the conductor, causing an induced electric current in the conductor.

13.1 Faraday’s Ring Faraday demonstrated electromagnetic induction using a device known as Faraday’s Ring. Closing the switch in the primary coil causes current to flow through the primary circuit conductor, producing a magnetic around the primary coil. As the magnetic field grows around the soft-iron ring from zero to maximum strength, it induces a voltage and current in the secondary coil, until the magnetic field becomes stable. Once stable, no current is induced. When the switch is opened, current stops flowing in the primary coil, collapsing the magnetic field from maximum strength to zero; once again inducing a current in the secondary coil, however in the opposite direction.

13.1 Factors Affecting EM Induction Several factors determine the amount of current that can be produced by electromagnetic induction: A coiled conductor has more induced current than a straight conductor. The greater the number of loops in a coil, the more electric current can be induced. A higher rate of change of the magnetic field; For a coiled conductor and permanent magnet, the more quickly you move the magnet into and out of the coil, the greater the induced current. The stronger the inducing magnetic field, the greater the induced current.

13.1 Applications of EM Induction Induction Cooking Cooking using an induction stove involves a rapidly changing magnetic field in the stove element, which induces an electric current in a metal pot. The pot heats up due to its internal electrical resistance. Iron pots work better than aluminum or copper because of its higher resistance. Glass pots will not work because they are insulating materials. Induction cooking is more efficient because there is a more direct thermal energy transfer to the food. Cooking surfaces do not get hot, so spilled food will not burn

13.1 Applications of EM Induction Metal Detectors Metal detectors use a coil that produces a rapidly changing magnetic field. This magnetic field induces a current in any metal near it. The induced current induces its own magnetic field which is read by sensitive measuring instruments. Metal detectors have many practical uses including: Locating buried bombs called land mines Security purposes at airports, special events Hobbyists searching for valuable buried metals

13.1 Implications of Faraday’s Discovery The implications of Faraday’s discovery were extraordinary because electricity was generated for the first time using only a magnet. Before Faraday’s experiments, the only way to produce electrical energy was to use an electric cell or battery. Batteries were could only operate for a limited amount of time, were heavy and bulky, and could only produce a small amount of electric potential. With Faraday’s discovery, all that was required was a method to keep a magnet moving continuously in order to produce electrical energy on a large scale without the limitations of batteries.

13.1 Homework Questions # 1-5 p.591