<img src="https://d5nxst8fruw4z.cloudfront.net/atrk.gif?account=iA1Pi1a8Dy00ym" style="display:none" height="1" width="1" alt="" />
Skip Navigation
Our Terms of Use (click here to view) have changed. By continuing to use this site, you are agreeing to our new Terms of Use.

Generators and Motors

Electrical or kinetic energy can be generated using principles of magnetism.

Atoms Practice
Estimated3 minsto complete
Practice Generators and Motors
This indicates how strong in your memory this concept is
Estimated3 minsto complete
Practice Now
Turn In
Faraday Flashlight

Faraday Flashlight

Credit: Chetvorno
Source: http://en.wikipedia.org/wiki/File:Linear_induction_flashlight.jpg
License: CC BY-NC 3.0

Rather than using batteries, a Faraday flashlight is powered by mechanical means. The flashlight is shaken by the users hand, and this energy is used to create a stored charge. It operates by the laws of induction and stores the current that is created in a capacitor.

News You Can Use

  • Mechanically powered flashlights rely on an external source such as human muscle to generate the electricity needed to power the light bulb. These types of flashlights do not need any batteries or external electrical connections. Faraday flashlights or ?shake flashlights? generate electricity based on Faraday's law. This law states that an induced emf is equal to the rate change of the magnetic flux.
  • Mathematically this is represented as:

\begin{align*}\epsilon=\oint - \frac{d\phi_m}{dt}\end{align*}

The right hand side of the equal sign is the time rate of change of the magnetic flux.

  • The shake weights in the flashlight consist of an electrical generator, a component to store the electricity (usually a capacitor and an LED lamp). The electrical generator consists of a very strong magnet that is able to slide back and forth through the center of a solenoid (a slinky shaped wire). As the magnet moves through the solenoid, a current is created and that current charges the capacitor. When an operator pushes the button to connect the circuit between the capacitor and the LED lamp, light is produced.
  • Watch this simple video which demonstrates Faraday's Law: 


Explore More

Using the information provided above, answer the following questions.

  1. Why does a stationary magnet in a coil not produce a current?
  2. What is the magnetic flux?
  3. Does the current change direction depending on which way the magnet is moving with respect to the coil?

Notes/Highlights Having trouble? Report an issue.

Color Highlighted Text Notes
Please to create your own Highlights / Notes
Show More

Image Attributions

  1. [1]^ Credit: Chetvorno; Source: http://en.wikipedia.org/wiki/File:Linear_induction_flashlight.jpg; License: CC BY-NC 3.0

Explore More

Sign in to explore more, including practice questions and solutions for Generators and Motors.
Please wait...
Please wait...