Practical Devices That Use Electromagnetic Induction

All flashcards

What does Faraday’s law say about induced emf?

An emf is induced when magnetic flux through a circuit changes. For a coil with $N$ turns, $\varepsilon = -N\frac{d\Phi_m}{dt}$; the minus sign represents the opposition described by Lenz’s law.

What is giant magnetoresistance?

Giant magnetoresistance is a large change in electrical resistance caused by a magnetic field in thin films with alternating ferromagnetic and nonmagnetic layers. It is used to detect magnetic patterns in modern hard-drive readout.

How does a passive graphics tablet use induction?

A magnetic pen moves above wires beneath the screen. Its changing magnetic field induces signals in the wires, and the tablet uses those signals to determine the pen’s position.

How does a shake-powered flashlight store energy?

Moving a magnet through a coil changes magnetic flux and induces current. That current charges a capacitor, which stores energy to power the light.

What is regenerative braking?

Regenerative braking makes an electric or hybrid vehicle’s motor act as a generator while braking, converting some kinetic energy into electrical energy that can be stored in the battery.

Quiz questions

1. What physical change is required for Faraday’s law to produce an induced emf?Answer: The magnetic flux through a circuit must change.
2. How does giant magnetoresistance help modern hard-drive readout?Answer: A magnetic field changes layered films’ resistance, revealing magnetic data patterns.
3. How does a passive graphics tablet detect a moving pen?Answer: The pen’s changing magnetic field induces signals in wires beneath the screen.
4. What happens to energy during regenerative braking?Answer: The motor generates electricity from some vehicle kinetic energy for the battery.
5. A magnet remains motionless inside a coil, and the magnetic flux stays constant. What induced emf results?Answer: No emf is induced while the magnetic flux remains constant.