Flashcards in Section 6 - Electric and Magnetic Fields Deck (40):
What causes a build-up of static?
Friction between two insulators.
What is the rule for the interactions between charges?
Opposite charges attract, like ones repel.
How do electrically charged objects attract uncharged objects? What is it called?
The charged object's charges repel or attract the electrons on the surface of the other object, this creates a charged surface that is attracted to. This is known as attraction by induction.
What are sparks? What causes them?
A large enough potential difference between an object and the earth. The spark is the electrons jumping from the object to the earth.
What are common uses of static electricity?
Photocopiers, paint and insecticide sprayers, industrial chimney protection.
What are the dangers of static electricity?
Static can build up when refueling and cause an explosion.
Static can build up in an airplane and disrupt communications.
How can electrostatic charge build-up be prevented and dissipated?
By earthing the object.
What is an electric field?
The region around a charged object where, if a second charged object were to be placed inside, a force on both of the charged objects would exerted.
What happens to electric field strength as you get closer to the object creating it?
How do electric fields explain sparking?
Statically charged objects create their own electric field, sparks are caused by a high enough potential difference that causes electrons to be removed from air particles, causing ionisation. ionized particles are often highly conductive and so current flows, this is the spark.
What is a magnetic field?
The region around a magnet where, if another magnetic or magnetic material were to be placed inside, a force would be placed on all the objects in the field, provided they were magnetic or magnets.
What is the rule between magnetic poles and their interactions with one another?
Like poles will repel one another where opposite poles attract.
How do compasses work?
The compass contains a tiny, free spinning bar magnet, it will always line up with whatever magnetic field it is in, this is most often Earth's.
What does the fact that the Earth produces its own magnetic field show about the earth's core?
That its core must be magnetic.
What are the three magnetic metal elements?
Iron, nickel and copper.
What must the magnetic force between a magnet and a magnetic material always be?
What are the two types of magnet?
Permanent and induced.
What types of magnetic material are there? What differentiates them?
Soft and hard, magnetically soft materials demagnetise very quickly and easily where magnetically hard materials are harder and take longer times to demagnetise.
What are some common uses of magnetic materials?
Fridge doors, cranes, doorbells, magnetic separators, maglev trains, MRI machines, speakers and microphones.
What happens when a current flows through a long, straight conductor?
A magnetic field is created around it, as a series of concentric rotating circles.
What happens to the magnetic field around a current carrying wire the closer you get, or the larger the current through the wire?
The field becomes stronger.
What technique can be used to find the direction of a field around a current carrying wire?
The right-hand thumb rule.
What is the motor effect?
Where a current carrying wire is put between magnetic poles, the magnets exert a force on the wire.
Describe the equation for the force acting on a conductor in a magnetic field.
F = Force
B = Magnetic flux density
I = Current
l = Length
What happens to a current carrying coil of wire in a magnetic field?
What is the structure of a motor?
A split-ring communicator
A coil of wire
What is a split-ring communicator?
A ring that is split in half so that the direction of the current changes every half turn.
What is a solenoid?
A long coil of wire.
How does a changing magnetic field affect a conductor?
It induces a potential difference.
How can an induced current in a conductor be increases?
By increasing the strength of the magnet, the number of coils and the speed that the magnet moves.
How do transformers work?
By using induction the size of the potential difference of an alternating current can be changed.
This is because the iron in the core is easily magnetised and demagnetised so as the current alternates, so does the magnetic field.
This causes a current with equal power in the secondary coil as in the primary coil.
The number of coils causes a change in potential difference and current between the coils.
Describe the formula for power either side of a transformer.
Vₚ = Voltage of the primary coil
Iₚ = Current of the primary coil
Vₛ = Voltage of the secondary coil
Iₛ = Current of the secondary coil
What are dynamos?
What are alternators?
What is the structure of a dynamo?
Split ring communicator
What is the structure of an alternator?
How do microphones work
Sound waves hit a flexible diaphragm, which is connected to a coil of wire.
The coil moves between two magnets causing an induced current.
How do speakers work?
A current is passed through a wire between two magnets, causing the coil to move.
The coil is connected to a cone which causes a sound wave.
How do power stations work?
By burning fuels, they heat water into steam which turns a turbine connected to a massive alternator.