Physics Test 2 part 1 Flashcards
How many volts does a diagnostic imaging department use?
440 volts or less
Transformer
is a device that increases or decreases the voltage without the use of any moving parts or any electrical contact between the two circuits and employs the principle of electromagnetic induction.
How many coils does a transformer consist of?
2
Primary coil
coil hooked up to the power source. A magnetic field is produced here through electromagnetism
Secondary coil
coil hooked up to whatever is using the power. Voltage is induced here through electromagnetism
Transformer Law Part 1
Deals with changes in voltage
Vs / Vp = Ns / Np
Vs = Secondary Voltage
Vp = Primary Voltage
Ns = Secondary number of coils (turns)
Np = Primary number of coils (turns)
Step up transformer
Any transformer that increases the voltage. Have a turns ratio greater than 1. There are more coils on the secondary side vs primary side.
Step down transformer
decreases the voltage
Transformer Law part 2
Deals with changes in current
Is / Ip = Vp /Vs
Why do transformers only operate on AC?
They are designed to work only with alternating currents
Air core transformer
The simplest type of transformer consisting of two insulated coils lying side by side with only air separating the coils
Open core transformer
An iron core is inserted into each coil of an air core transformer
Flux leakage
Magnetic lines are lost from an open core transformer
Closed core transformer
The coils are wrapped around an iron square.
Shell-type transformer
Both the primary and secondary coils are wrapped around the central section of the core to increase efficiency.
Most efficient but most expensive
Autotransformer
A transformer that works on the principle of self induction, because it only has one coil.
Also known as a variable transformer
Autotransformer Law
Deals with voltage produced
Vs / Vp = # of tapped turns/ total # of turns
What do x-ray machines contain?
at least an autotransformer, a step-up transformer and a step-down transformer.
How many possible causes of power loss is there?
4
flux leakage
Copper loss
Eddy current loss
Hysteresis loss
Copper loss
Since long lengths of copper wire are used in the construction of a transformer, resistance exists which causes heat.
This can be minimized by having an adequate diameter wire.
Eddy current loss
Will occur only when iron is used in the core.
Since iron is a conductor, it is in the changing magnetic field which creates a current within it.
The current will swirl around the iron core
Hysteresis loss
Since the magnetic field of the primary coil is continuously changing, the magnetic domains of the iron core must continuously rearrange themselves to the magnetic field.
This increases the motion of the atoms in the core, causing heat
How many possible devices are there for current regulation?
4
Rheostat
Choke coil
Saturable reactor
High frequency circuit
Rheostat
also called a potentiometer.
A variable resistor is added to the circuit that regulates resistance and therefore current according to Ohm’s Law.
These can be used as mA selectors and in electric timers.
Choke coil
Works on the principle of self induction and requires AC to work.
It consists of a coil of wire and an iron core.
Saturable reactor
Also known as magnetic amplifiers, saturable reactors use a DC control winding to control the flow of AC current in a circuit.
High frequency circuit
A computerized method of current regulation that requires advanced circuitry.
