Magnetism & Electromagnetism Flashcards
Name three Ferri magnetic materials
Iron steel nickel cobalt
What are the two proven characteristics of flux linea
- It acts in a definite direction
2. It appears endless
What are the five properties of magnetic fields?
- They always form a complete loop.
- The never cross one another.
- They have a definitive direction north to south.
- They try to contract.
- They repel one another when lying side by side in the same direction.
How may as magnet lose it magnetism ?
- A sharp shock from a fall
2. Heat
What are keepers ?
Soft iron plates placed at the ends of magnets to help keep their magnetism
What are magnets that resist demagnetisation called ?
Hard magnets (alnico & permalloy)
How does a magnetic field react with a non magnetic material?
It has no reaction
How does a magnetic field react to a magnetic material ?
Flux line become concentrated in the material.
What occurs when a conductor Carrys a current ?
It forms a magnetic field around the conductor.
If the current is flowing away from you in what direction is the magnetic field flowing ?
Clockwise
If the current is flowing towards you what direction is the magnetic field flowing ?
Counter clockwise
What is the symbol for current flowing away from you ?
Cross
What is the symbol for current flowing towards you ?
Dot
What is the right hand grip rule ?
Thumb points of right hand points in direction of current.
Finger curl in direction of magnetic field.
What force is induced in to cables side by side one with current flowing away and one with current flowing towards you ?
They will repel each other
What force is induced in two cables side by side when they are both running towarda or away from you ?
They will attract eack other.
What is a solenoid ?
It is a insulated conductor wound into many circular coils or turns.
What determans the strength of the magnetic field of a solenoid ?
- Value of current flowing through it.
2. Number of coils in the soleniod.
What happens when a solenoid is wrapped aroud a conductor and current is passed through the solenoid ?
It cause the conductor to become magnetised as long as the solenoid in carry current
Name three examples of a electromagnet ?
Bell, MCB , RCD
What is Flemming right hand rule uses for ?
Motors.
Explain Flemming’s right hand rule ?
Thumb is movement of conductor
Index finger is magnetic field direction
Second finger is current direction
What does faradays law state ?
If a coil is placed in the region of a changing magnetic flux an EMF will be induced in the coil.
Explain dynamic induction ?
Dynamic Induction is movement of a flexible conductor through a permanent magnet thus inducing a EMF(electro magnetic force)
Exp. Generator
What are the factors effecting the value of a EMF (E) induced in a coil ?
Strength of magnetic flux (B)
The length of the conductor (L)
The velocity of the conductor passing through the magnetic field (V)
E=B x L x V
What is Flemming right hand rule uses for ?
Generators.
Explain Flemming’s right hand rule ?
Thumb= movement of conductor
Index finger = magnetic field direction
Second finger = current direction
What does lenzs law state ?
The direction of the induced EMF is always such that it opposes the motion producing it.
What is inductance ?
Inductance is the opposing force to the changing current in a circuit/coil
What is the unit of inductance ?
Henry (H) symbol (L)
What are the Factors that determine the Inductance of a coil ?
The number of turns forming the coil .
The diameter of the coil.
The core material.
Explain static Induction ?
Static Induction is when a current is passed through a coil to induce a magnetic force large enough to interact with another coil close by thus inducing a EMF in the second coil.
ie. Shaver sockets
