P15 - Magnetism Flashcards
What is a magnetic field?
The space around a magnet
or the space around a current-carrying wire
What is induced magnetism?
• the magnetism of an unmagnetised material by placing it in a magnetic field
How does induced magnetism work?
• an unmagnetised iron rod placed in line with a bar magnet becomes magnetic with poles as each end
• the nearest poles of the rod and the bar magnet have opposite polarity
• induced magnetism will cause a force of attraction between any unmagnetised magnetic material placed near one end of a magnet
• the force is always attractive
What is the direction of a magnetic field?
Always points from North to south
The Earth’s magnetism
• magnetic compasses point to the Earth’s pole due to the Earth’s magnetic field
• magnetic compass contains a small bar magnet
• compass needle points in direction of the magnetic field
• our compasses point to North because our compasses point to geographic North (not bar magnet North)
Magnetic materials
• iron, steel, nickel and cobalt
not all metals are magnetic - aluminium is not magnetic, nothing will happen if it is placed in a magnetic field
What are permenant magnets?
• made of steel because magnetised steel does not lose its magnetism easily
What is electromagnetism?
You can make it magnetic
• an insulated wire wrapped around an iron bar that becomes magnetic when there is a current in the wire
What is electromagnetic induction?
• process of inducing a potential difference in a wire by moving the wire so it cuts across the lines of force of a magnetic field
What is an alternator?
• an alternating current generator
What is a dynamo?
• a direct current generator
What is Fleming’s left hand rule?
• a rule that gives the direction of the force on a current-carrying wire in a magnetic field according to the directions of the current and the field
What is the generator effect?
• the production of a potential difference using a magnetic field
What is a magnetic field line?
Line in a magnetic field along which a magnetic compass points - also called a line of force
What is magnetic flux density?
A measure of the strength of the magnetic field defined in terms of the force on a current-carrying conductor at right angles to the field lines
What is the motor effect?
When a current is passed along a wire in a magnetic field, and the wire is not parallel to the lines of the magnetic field, a force is exerted on the wire by the magnetic field
What is a solenoid?
A long coil of wire that produces a magnetic field in and around the coil when there is a current in the coil
What is a split ring commutator?
• metal contacts on the coil of a direct current motor that connects the rotating coil continuously to its electric power supply
What is a step down transformer?
Electrical device used to step-down the size of an alternating potential difference
What is a step up transformer?
• electrical device that is used to step up the size of an alternating potential difference
What causes simple motors to rotate?
• when an electric current flows through a wire, it creates a magnetic field around the wire
• if this wire is placed within another magnetic field (created by a permanent magnet or electromagnet) the interaction between these two magnetic fields results in a force being exerted on the wire
• the forces act on the sides of the coil in opposite directions, causing the coil to rotate
How does an ignition circuit work?
closing the (ignition) switch causes a current to pass through the electromagnet
the iron core becomes magnetised
the electromagnet attracts the iron arm
the iron arm pushes the starter motor contacts together
the starter motor circuit is complete
a current flows through the starter motor (which then turns)
