Assignment 12- Electromagnetic Induction (2)

# Assignment 12- Electromagnetic Induction (2) - Basic...

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Picture 16 Basic Properties of Inductors Learning Goal: To understand the units of inductance, the potential energy stored in an inductor, and some of the consequences of having inductance in a circuit. After batteries, resistors, and capacitors, the most common elements in circuits are inductors. Inductors usually look like tightly wound coils of fine wire. Unlike capacitors, which produce a physical break in the circuit between the capacitor plates, the wire of an inductor provides an unbroken continuous path in which current can flow. When the current in a circuit is constant, an inductor acts essentially like a short circuit (i.e., a zero-resistance path). In reality, there is always at least a small amount of resistance in the windings of an inductor, a fact that is usually neglected in introductory discussions. Recall that current flowing through a wire generates a magnetic field in the vicinity of the wire. If the wire is coiled , such as in a solenoid or an inductor, the magnetic field is strongest within the coil parallel to its axis. The magnetic field associated with current flowing through an inductor takes time to create, and time to eliminate when the current is turned off. When the current changes, an EMF is generated in the inductor, according to Faraday's law, that opposes the change in current flow. Thus inductors provide electrical inertia to a circuit by reducing the rapidity of change in the current flow. Inductance is usually denoted by and is measured in SI units of henries (also written henrys, and abbreviated ), named after Joseph Henry, a contemporary of Michael Faraday. The EMF produced in a coil with inductance is, according to Faraday's law, given by . Here characterizes the rate at which the current through the inductor is changing with time . Part A Based on the equation given in the introduction, what are the units of inductance in terms of the units of , , and (respectively volts , seconds , and amperes )? ANSWER:

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Picture 18 Picture 20 Picture 2 Picture 24 Basic Properties of Inductors Part A Correct Part B What EMF is produced if a waffle iron that draws 2.5 amperes and has an inductance of 560 millihenries is suddenly unplugged, so the current drops to essentially zero in 0.015 seconds? Express your answer in volts to two significant figures. ANSWER: The elevated voltage does not last long, but it can sometimes be large enough to produce a potentially dangerous spark. Moral: Be very careful when opening switches carrying current, especially if they are part of an inductive circuit! Electrical potential energy is stored within an inductor in the form of a magnetic field when current is flowing through the inductor. In terms of the current and the inductance , the stored electrical potential energy is given by .
Picture 31 Picture 32 Picture 3 Picture 35 Picture 36 Basic Properties of Inductors Part C Which of the following changes would increase the potential energy stored in an inductor by a factor of 5? Check all that apply.

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Assignment 12- Electromagnetic Induction (2) - Basic...

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