Magnetism And Electro Magnetism Flashcards
What are the most common magnetic materials?
Iron
Steel - alloy of iron and carbon
Cobalt
Nickel
What are magnetic fields
A bar magnet and the earth are surrounded by magnetic fields
These fields allow magnets to exert forces on other magnets
On a bar magnet the poles are the regions where the field is strongest
A freely hanging bar magnet will align north to south
North Pole of magnetic points to geographic north
- used for compass for navigation or plotting compass to find magnetic field around a magnet
What are magnetic field lines
They show the movement, direction or shape of a magnetic field
They never cross or touch
Outside the magnet the direction of magnetic field lines are north to south
A plotting compass aligns to point along the magnetic field towards the South Pole of bar magnets
Where field lines are closest the field is strongest
What is a uniform magnet field
The strength and direction of the field do not change
Field lines are parallel and evenly spaced
What are the key rules about magnetic forces
2 bar magnets close to each other will attract or repel
Like poles repel
Opposite poles attract
How are materials magnetised
Magnetically soft materials eg iron easy to magnetise and demagnetise
Magnetically hard materials eg steel are difficult magnetise and keep their magnetism for a long time
A permanent magnet eg a bar magnet can temporarily magnetise a magnetically soft object eg a nail.
Explain temporary magnetism
a magnetic field of a permanent magnet eg bar magnet can temporarily magnetise a magnetically soft object
The end of an object near to the North Pole of the bar magnet becomes a South Pole
The object is attracted to the bar magnet
Eg So a magnet could pick up several paper clips or nails
How do you predict the direction of a magnetic field - straight wire
Right hand grip rule
Point your thumb in the direction of current
Your fingers wrap in the direction of the magnetic field
How do you predict the direction of the magnetic field - coil wire
Right hand thumb rule
Wrap fingers in direction of the current
Your thumb points to the North Pole of electromagnet
How do you predict the direction of the field - solenoid
Right hand thumb rule
Wrap fingers in direction of current
Thumb points to North Pole of electromagnet
What are solenoids
A cylindrical coil of wire carrying electrical current
Around a short coil there is a magnetic field similar to that around a bar magnet
Use right hand thumb to find north
Outside solenoid field runs from north to south
Field lines pass through inside of coil from south to north
Reverse direction causes reverse of magnetic field direction
How can a solenoid become an electromagnet
Place piece of soft iron inside the coil
The magnetic field of the coil magnetises the iron nail
Magnetised iron increases strength of the electromagnet
Use a magnetically soft material so it demagnetises quickly when current switched off
Why should the wire be insulated
To prevent current flowing through the nail
Or passing from coil to coil and creating eddy current which would stop solenoid acting as electromagnet
How do you increase strength of the electromagnet
Increasing current
Increasing number of cells
What are common uses of electromagnets
Electric bells
Door locks
