Chapter 13 Electromagnetism Flashcards
What are permanent magnets
Magnets made of steels as magnetised steel doesn’t loose its magnetism easily
4 examples of magnetic metals
Iron
Cobalt
Nickel
Steel
What is a magnetic field
The region around the magnet. Any other magnetic material placed in this space experience a force cased by the first magnet
Steps to plot a magnetic field
- With magnet in the middle of paper, use a pencil and plot a dot on paper where needle is pointing from the compass in one the corners.
2.then place the compass so that the needle points to the dot you have made
- Draw a new dot at the other end of the needle
- Keep going until you go off the page or loop back around to the other side of the magnet
- Keep repeating this process completing many lines as possible using different starting points.
Features of the shape of a magnetic field (2 points)
-The strongest the field is by the poles
-The weakest the field is further away from the poles
What is induced magnetism
Magnetism created in an unmagnetised magnetic material when the material is placed in magnetic fireld
Why does the holder of an electromagnet be made of plastic
As its an insulator and doesn’t conduct electricity and doesn’t intervene with the magnetic field
What rule do you use to find the direction of the field around a straight wire and what is it
The right hand grip rule where your thumb points along the direction of the current and your other fingers give the direction of the field
What is a solenoid
A wire coiled into a spiral
Describe what happens inside and out the solenoid
Inside: magnetic field is much stronger than if the wire was straights. Field lines are parallel to the axis of the solenoid and are all in the same direction (uniform), the magnetic field inside a solenoid is strong and uniform
Outside: magnetic fields bend around from one end to the other. The magnetic field outside is like the field of a bar magnet except each field line is a complete loop
3 ways to make the field around a solenoid stronger
-increase current
-add more turns to the coil
-add an iron core(making an electromagnet)
What is an electromagnet
A solenoid in which the isolated wire is wrapped around an iron bar. When current is passed along a wire, a magnetic field is created around the wire, due to this the magnetic fields of wire magnetised the core(iron). An advantage is that it can be switched on and off the move heavy things
How to increase the magentic field strength on an electromagnet
-Increase size of current
-increase coil turns
What is the motor effect
When a conductor carrying a current is placed in a magnetic field the magnet producing the field and the conductor exert a force in each other. This is called the motor effect
What factors impact the size of the force produced on the current carrying wire
-increasing the current
-using a stronger magnet
What position is strongest and zero regarding the motor effect
Greatest when wire is perpendicular to the magnetic field and zero when wire is parallel to the magnetic field
What is Flemings left hand rule and what does the fingers represent
The relative orientation of the force, the current in the conductor and the magnetic field.
First finger = Field(north to south)
Second finger = Current(+ to -)
Thumb = Movement(force in or out of page)
Force on conductor and magnetic flux density equation
Force = magnetic flux density X current X length
F(newtons) = B(teslas) X I(amperes) X L(M)
How does a DC motor turn
When an electric current passed through a coil in a magnetic field, the magnetic forces produces a turning effect which turns a DC motor
How to change speed and direction of the motor
- Increase the current or strength of field to increase speed
- Reverse direction of the current to change direction
What is the problem with the motor effect
When the wire loop flips over the forced are reversed which wouldn’t create a continuous motion but this is solved with a split ring commutator
What is a split ring commutator
The brushes from the power supply contact the commutator meaning that the direction of current can he reversed whenever the ring swap sides so the motor always spins in the same direction
