Electrodynamics Flashcards
where does a magnetic field exist
It exists around a permanent magnet or a current carrying conductor
What are the factors that affect the magnitude of a current carrying conductor (increase) f=ILBSin0
1-increase the length of the conductor between magnetic field ( add loops)
2-increase the current
3-increase the emf of the conductor
4-strength of the magnetic field
What do motors convert
electrical energy to mechanical energy
why will current carrying coil placed in an magnetic field turn
When a current flows through the coil windings in a magnetic field it will experience a turning force
Why does a dc motor have split rings
without split rings the dc motor will not rotate continuously and will get stuck in a vertical position. The split ring commutator will reverse the direction of the current in the armature every half rotation allowing the motor to rotate continuously in one direction.
State Faradays law
The emf induced is directly proportional to the rate of change of magnetics flux
State Lenzs law
The induced current flows in a direction so as to set up a magnetic field to oppose the change in magnetic flux
What do Ac Generators convert
Mechanical to electrical energy
Why are slip rings used in an AC generator
reverse the current every half turn
State Magnetic flux density
A representation of the magnitude and direction of the magnetic field.
State magnetic flux linkage
The product of the number of turns on the coil and the flux through the coil.
Explain the basic principle of the AC generator
Converts Mechanical energy to electrical energy
When a coil is rotated through a magnetic field there is a chnage in flux. According to Faradays law, if threes a change in flux an emf will be induced in the coil which induces a current. A slip ring is used in the AC generator, the current is revered every half turn
What is the principle of a Transformer
They are used to step up or step down the voltage of alternating current
- When alternating current flows through the primary coil, a changing magnetic field is induced therefore change in magnetic flux
- The changing magnetic flux is transferred through the iron core to the secondary coil
- The is creates a changing electric filed in the secondary coil. According to Faradays law, this change in flux is due the changing magnetics filed will induce a changing emf and current in the secondary coil
What is an ideal transformer
input power=output power
What are the advantages of having high voltage low currents for transmission
The power transmitted at a high voltage and low current to minimise power loss on the transmission line
When current flows in the transmission it heats up the wire and the power is converted to heat energy .
for the equation p=(i)2R, power is directly porportinal to the square of the cureent. This means the greater the current in the line the more power is lost in transmitting it
