4.5 electromagnetic effects Flashcards
how can an emf in the conductor be induced?
by moving a conductor across a magnetic field or changing magnetic field linking with a conductor
factors that affect the magnitude of an induced emf
- the speed at which the wire, coil or magnet is moved
- the number of turns on the coils of the wire
- the size of the coils (bigger area = bigger field)
- the strength of the magnetic field
construction of a simple transformer
soft iron core used for voltage transformations
step up transformer
increases the potential difference of a power source
- has more turns on secondary than primary coil
step down transformer
decreases the potential difference of a power source
- fewer turns on secondary coil than primary
transformer roles in high voltage transmission
- used to increase the voltage of electricity before it is transmitted across the national grid
- used to lower the high voltage electricity used in power lines to lower voltages used in houses
- used in adapters to lower mains voltage to lower voltages used by many electronic devices
advantages of high voltage transmission
When electricity is transmitted over large distances the current in the wires heat them, resulting in energy loss
To transmit the same amount of power as the input power the voltage should be increased
- results in a smaller current being transmitted bcs P = IV
Smaller current flowing through the power lines result in less heat being produced
simple d.c motor consists of:
a coil of wire (that is free to rotate) positioned in a uniform magnetic field
how does a d.c motor work? (without split ring first)
When a d.c current is passed through the wires it creates a magnetic field.
This mag field interacts with the mag field of the magnets, resulting in a force being exerted on the coil (direction determined by flemings right hand rule)
As current flows in opposite direction on each side of coil the force will be exerted on different sides (up/down) causing the coil to rotate.
The coil will continue rotating until the vertical position.
what does a split ring commutator do in a d.c motor?
reverses the direction of the current in the coil every half turn
- keeping the coil rotating continuously as long as current is flowing
how to increase the speed the coil rotates (d.c motor)
- increasing the current
- using a stronger magnet
how to change the direction of rotation of coil (d.c motor)
- reversing the direction of current
- reversing the poles of the magnet
how to increase the force supplied (d.c motor)
- increasing the current in the coil
- increasing the strength of the mag field
- adding more turns to the coil
transformer
an electrical device that can be used to incresae or decrease the pd of an ac
- by the generator effect
what does a basic transformer consist of
primary coil
secondary coil
soft iron core
why is a iron used in transformers
because iron is easily magnetised (its a soft magnetic material)
operation of a transformer
- ac supplied to PC
- ac produces a changing mag field around PC
- mag field passes through iron core
- changing mag field inside SC
- induces an alternating pd on the SC
- (if SC is part of complete circuit an ac will flow)
generator effect
the induction of EMF, therefore producing an induced current when a wire experiences a changing magnetic field
equation for 100% efficiency in a transformer
IpVp = IsVs
p (primary coil)
s (secondary coil)
Power equation with current and resistance
current^2 x resistance
why is power loss in cables smaller when the voltage is greater?
the higher the voltage, the lower the current (P=IV) through the wire. since I^2 is directly proportional to power, for a small current power loss is also small.
