Do electromagnets create electric fields?
If I use an electromagnet (let's say a solenoid) and turn the circuit on and off and on and off, does that change the B in the magnetic flux equation (Im=BAcos@) and thus changes the induced emf? (emf= change in magnetic flux/change in time). Would this change in emf then mean I'm creating an electric field?
Tell me if that is correct physics-wise please!! I need to know before a physics presentation tomorrow.
Update:Thanks so much RickB! Just to work off of that- does that mean that this electromagnet turning off and on would be emitting electromagnetic waves because the electric and magnetic fields are changing? If so, what kind of electromagnetic waves might they be? (radio, microwave, etc?)
Comments
Yes electromagnets create electric field, thats why its called ELECTROmagnet. However, an steady or constant electromagnetic field will not produce induced emf. Everytime you turn your solenoid on and off, the magnetic field (B) does the same thing but in slower rate. The faster you turn your solenoid on and off, the more induced emf you produced. Lets take a transformer for example. A common transformer have two windings, a primary and secondary, (winding means a wire being wrap around a core, windings is the same as coils.). This windings are in close proximity to each other but don't actually have a physical contact. The primary winding is conected to our electric outlet at home with 110V and 60hz. The primary winding will now act as an electromagnet. Since the primary winding is connected to 110V 60hz, that means that the B or the magnetic field changes or turn on and off 60 times per second. As a result, a voltage (emf) will be present at the secondory winding even the two wires or windings doesn't have a physical contact. The voltage that is produced in our secondary winding is the induced emf. If we change our outlet to 110V 0hz. No voltage or induced emf well be present at our secondary winding since the magnetic field (B) is not changing.
So you are right!! emf=change in magnetic flux/change in time.
For your additional question; yes! changing elecromagnetic field also emits electromagnetic waves. What RickB was talking about lighting a light bulb without contact is a form of electromagnetic induction same principle of how transformers work (we need some kind of a electromagnetic receiver circuit to light a light bulb with electromagnetic wave emision not just a coil). Electromagnetic induction is totaly defferent than electromagnetic wave emision. Electromagnetic induction only works at close proximity but electromanetic waves can travel at great distance. Back to the transformer example. The 110V 60hz electrical outlet we got at home is changing its electromagnetic field 60 time a second therefore emitting electromagnetic wave with a frequency of 60hz. Our outlet now acts as an electromagnetic transmetter. Our outllet however have a relatively low frequency to produce microwave or even radio wave. We need some kind of an ocillator to do so.
Good luck on your presentation tommorw. Don't worry, you'll be fine!
hope this helps a bit!
> Would this change in emf then mean I'm creating an electric field?
Yes. In fact, that's how transformers work. In a transformer, one coil of wire acts as an electromagnet. Its magnetic polarity is switched back and forth many times per second, and that induces an electric field (and current) in a second coil of wire (usually at a different voltage).
I've seen demonstrations in which a rapidly switching electromagnet is placed (wihtout touching) within a coil of wire that's connected to a small light bulb; and the induced field is strong enough to actually light up the light bulb. (You need a pretty powerful electromagnet to make this work.)