Electromagnets & EM induction Flashcards
(19 cards)
Rules for magnetic field lines
- they never touch or cross
* goes from north to south outside the device
Methods of magnetizing and demagnetizing steel
can be magnetized with stroking method and an electrical method, is ‘hard’ and therefore doesn’t demagnetize
what is the domain theory
When the domains(tiny cells) in a material are all lined up in the same direction the material is magnetized, they are pointing different directions in an unmagnetised material.
uses of permanent magnets
-automobiles
-
What was oersted’s discovery
He discovered that around a wire carrying a current there is a magnetic field. He found this by holding a wire over and parallel to a compass needle which is pointing N and S, the needle moves when the current is switched on. Reversing the current reversed the way the needle went.
what is an electromagnet
Coil wrapped around a shot iron core
How can you increase the strength of an electromagnet
- increasing current
- increasing the number of turns
- inserting a soft iron core
Uses of electromagnets
- Junk yard crane
- Circuit breaker
- Some motors
- generators
- loudspeakers
What is the motor effect
When a current carrying wire is placed in an external magnetic field, experiences a force and interacts with each other.
How does a dc motor work
The rotating magnetic fields interact with the magnetic fields of the magnets in the stationary part of the motor (stator) to create a force on the armature which causes it to rotate
How to induce electromagnetic current
Current will be generated in a closed loop of conductor moving through magnetic field lines.
How does an ac generator work
dd
Characteristics of ac
- Direction of current changes periodically with time
- has a changing magnetic field
- When a conductor is placed this changing field and emf is induced in it.
what are the two types of transformers
- step-up
- step-down
Transformer formula
Vs/Vp=Ns/Np
What does a transformer consist of
primary coil and a secondary coil mounted on a core(loop) of laminated cost iron.
How does the transformer work
Alternating current flowing in the primary coil produces an alternating field which is conducted around the core causing an alternating e.m.f to be induced in the secondary coil.
What are ideal transformers + formula
100% efficient
- power delivered by the transformer= power consumed
- Vp x Ip = Vs x Is
What is the use of transformers in the national grid
The national grid supplies power to houses and factories, which have drastically different needs in terms of amount of voltage. To have the high voltage a factory may require in a house would be very dangerous. In addition when transporting a lower voltage we loose less energy.
