Electromagnetism Flashcards
Define magnetic field
A region of space within which a magnet experiences a force
Define plotting compass
A small compass used to find shape of a magnetic field
What are magnetic field lines
Lines drawn to represent a magnetic field
Where are the strongest points if the magnets
The poles (north and south)
Define solenoid
A coil of wire carrying an electrical current
Name the magnetic materials
Nickel, steel, iron and cobalt
In what direction do field lines always travel in
Flow from north to south
Properties of field lines
Never touch or cross
Crowd together in regions where field is strongest.
What is the right hand grip rule
When we wrap our right hand around the solenoid, fingers in direction of current, the thumb points to the North Pole.
How is an electromagnet effected by and increase in current, the amount of turns and the core?
These all increase magnetism
Method of practical to investigate effect on magnetism if current is increased in a solenoid
Construct an electromagnet
Connect to circuit with a battery, an ammeter and a rheostat. Have the same number of turns and increase the amps and count number of paper clips lifted by electromagnet.
We can do this to measure the effect of number of coils and the material of the core.
What does the thumb direction represent in Flemings left hand rule?
Force
What does the first finger represent in Flemings left hand rule
The magnetism direction
What does the second finger represent in Flemings left hand rule
The current direction
How does a simple dc motor work?
Applying Flemings left hand rule. Split ring commutator provide contact with power supply. Allows for positive and negative sides to not change when motor spins.
See page 12 of book or watch cognito vid
What instrument is used to demonstrate differences between A.C and D.C
Cathode Ray Oscilloscope
What is a d.c current
One that always flows in the same direction, from a fixed positive terminal to a fixed negative terminal.
What is an A.C current
One in which the voltage and hence current changes size and direction in a regular and repetitive way.
When is force in a current carrying conductor in a magnetic field strongest
When current, and field directions are perpendicular
Define electromagnetic induction (EMI)
Electromagnetic induction is the production of a voltage across an electrical conductor when the strength of the magnetic field around it changes.
Which factors affect the current that flows in an EMI
Moving the magnet faster
Using a stronger magnet
Using a coil with a greater number of turns
How is a current induced in a conductor by changing current in a neighbouring conductor
As the conductors are linked magnetically, if an increased magnetic field occurs due to a change in current there will be a small deflection witnessed in the other neighbouring conductor. See Farradays iron ring experiment on pg 121
What does a transformer do
They are devices which change the voltage of an a.c supply
What is the structure of a transformer
A primary voltage, flows into a primary coil wrapped around a soft iron core which also has another secondary coil wrapped around it which produces a secondary output voltage
What is the transformer equation
Vs➗Vp=Ns➗Np
Define a step-up transformer
A transformer in which the output voltage is greater than the input voltage (as output coil had more turns than input coil)
Define a step-down transformer
A transformer in which the output voltage is smaller than the input voltage (as output coil has fewer turns than input coil).
Why are a.c generators used in electrical generators.
Transformers are used in the process of transporting electricity around the country in order to save energy. Therefore D.C supply cannot be used as it creates a steady magnetic field which does not induce a current to flow just like a magnet held stationary beside a coil.
What does a simple a.c generator consist of
A coil rotating between the poles of a magnet
What are the main parts of the national grid system
Cooling towers, boilers, Steam turbine, generator, step up transformer, power lines, step down transformer
How are step-up and step-down transformers used in transmission?
A step-up transformer boots the voltage up, automatically reducing current value. This conserves power as a smaller current results in less heat energy/power lost from the cables
A step down transformer will then bring the voltage back down to around 240 volts for households
