Transcript Combustion Equation

Motors
Noadswood Science, 2013
Motors
Tuesday, March 29, 2016
To know how motors function and Fleming’s left hand rule
Magnetic Fields
• A magnetic field is a region where magnetic materials and also
wires carrying currents experience a force acting on them
• They can be represented using field diagrams (arrows from North
to South)
• Strengths of a magnetic field can be increased using a
magnetically “soft” iron core – these materials magnetise and
demagnetise easily (electromagnets)
Magnetic Field
• When a current flows through a wire a magnetic field is created
around the wire – the field is made up of concentric circles with the
wire in the centre – this is shown by the right-hand thumb rule
Magnetic Field
• The magnetic field inside a coil of wire (solenoid) is strong and
uniform, whilst outside the magnetic field is like that of a bar
magnet
Electromagnets
• When electricity is passed through a coil of wire, the coil has a
magnetic field around it – this is an electromagnet
• If the coil of wire is wrapped around a piece of iron, such as an
iron nail, the magnetic field gets stronger
Electromagnets
• A magnetic field is produced when an electric current flows
through a coil of wire - this is an electromagnet (a solenoid is a
long coil of wire)
• Electromagnets strength can be increased via
the following: – Wrapping the coil around an iron core
– Adding more turns to the coil
– Increasing the current flowing through the
coil
Electromagnets
• The magnetic field around an electromagnet is just the same as
the one around a bar magnet
• It can, however, be reversed by turning the battery around
• Unlike bar magnets, which are
permanent magnets, the
magnetism of electromagnets
can be turned on and off just
by closing or opening the
switch
Electromagnets
• More turns = stronger electromagnet
• More current = stronger electromagnet
• Iron core = stronger electromagnet as it increases the magnetic
field strength (plus iron is magnetically “soft” so it can be turned
on/off (steel is magnetically “hard”, retaining its magnetism (good
for permanent magnets))
Insulated wires
Core
Crocodile clips
Connecting wires
Power pack
The Motor Effect
• The motor effect is a force experienced by a current-carrying wire
in a magnetic field
• The force gets bigger if either the current or the magnetic field is
made bigger
• If the current of magnetic field direction is reversed then the
direction of the force is reversed too (this can be worked out using
Fleming’s left hand rule)
Fleming’s Left Hand Rule
• Fleming’s left hand rule shows which way a force will act: – Thumb shows motion
– First finger shows field
– Second finger shows current
Fleming’s Left Hand Rule
• For example, using Fleming’s left hand rule which direction is the
force on the wire…
Fleming’s Left Hand Rule
• Draw the current (+ve to –ve); apply the left hand rule and then
draw in the direction of force (motion)
Simple Electric Motors
• Simple electric motors are affected by current and the magnetic
field strength – if either of these is increased the speed of the
motor increases
• The forces are those found which act on any current in a magnetic
field, however as the coil is on a spindle the forces act one up and
one down (causing rotation)
Simple Electric Motors
• The split-ring commutator swaps the contacts every half turn
keeping the motor rotating in the same direction
• A simple motors direction can be reversed by swapping the
polarity of the direct current or swapping the magnetic poles
Simple Electric Motor
• Which way is the coil turning in this simple motor?
Simple Electric Motor
• Which way is the coil turning in this simple motor?
• Charged particle in a cathode ray tube
example.