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Physics Part II
motors, generators, transformers, autotransformers, rectification
| Question | Answer |
|---|---|
| What devices take advantage of the relationship between electricity and magnetism? | generator and motors |
| Generators utilize what law? | Faraday's law |
| What do motors convert? | electrical energy into mechanical energy |
| What does a generator convert? | mechanical energy into electrical energy |
| What are 2 components of a generator? | *magnet *an armature |
| What is an armature? | coil of wire rotated within a magnetic field. |
| What are the types of generators? | AC & DC |
| In generators, what is the relationship with the armature and magnetic field to produce a great induced current? | When the armature is perpendicular to the magnetic field the induced current is very strong. |
| Describe the components of an AC generator. | the conductors are slip rings connected to the armature. the slip rings have brushes on the outside made out of conductor. These brushes are connected to the AC power source. |
| What is the difference between an AC generator and a DC generator? | DC generator has commutator rings that have brushes on them instead of the slip rings. Commutators are like slip rings but separated into halves. |
| What happens when the armature is parallel to the magnetic field? | there is no induced current produced. |
| A conductor in motion inside a magnet produces what? | an induced current |
| Which generator has a commutator ring? | DC generator |
| Discuss how current is produced and moves through generators. | a coil of wire is placed in a strong magnetic field between 2 poles. the coil (armature) is rotated using mechanical E. Because the armature is in motion inside mag. field = induced current |
| T/F: DC motors use a rotating magnetic field. | False; AC induction motors do |
| What is the component that provides the rotating magnetic field in an induction motor? | stator |
| Which transformer causes voltage to increase & current to decrease? | step up transformer |
| What is the formula for turns ratio? | Ns/Np |
| A transformer has a turns ratio of 12:1. Is this a step down or up transformer? | step up transformers have more turns in the secondary than the primary. |
| In a step up transformer, what happens to the current/amperage in the secondary? | decrease |
| In what devices would you find commutators? | DC motors & DC generators |
| Transformers operate on the principle of what? | mutual induction |
| What kind of transformer will its voltage decrease and its current/amperage increase? | step down transformer |
| What are mutual induction devices which are used to change voltage & amperage/current? | transformers |
| How much the voltage & current changes in transformers depends on what? | the number of turns in the secondary divided by the number of turns in the primary. |
| What is the first form of the transformer law? | Ns/Np = Vs/Vp |
| If the turns ratio is 250:1, how do you put that in the turns ratio formula? | 250/1 |
| What is the second form of the transformer law? | Np/Ns = Is/Ip |
| If there is one turn on the primary and 10 turns on the secondary, which has more resistance? What happens to current? | secondary; because the longer the circuit = more resistance. the current decreases since resistance increase. |
| If an armature in an AC generator is turned counterclockwise, the induced current will flow which way? | clockwise |
| Which device converts mechanical energy into electrical energy? | generator |
| T/F: a side of an armature will switch its polarity from positive to negative and then from negative to positive according to whether it is going up or down in both AC and DC generators. | true |
| T/F: A current may flow directly from the stator to the rotor. | False; current can't flow if they are not touching |
| A device that includes a stator and a rotor is what? | an AC induction motor |
| Xray tubes use what kind of motor? | an AC induction motor |
| T/F: A DC generator uses 2 slip rings. | False; DC generators use commutators |
| T/F: In an AC generator, a slip ring will contact the positive side of the armature half of the time and it will contract the negative side half of the time. | true |
| T/F: There are 2 brushes used in both AC and DC generators. | true; the brushes are on the outside of either the slip rings or commutators and connect to the source voltage being used in the circuit connected. |
| T/F: Because the strength of the induced current in the armature of a DC generator increases to it greatest point and decreases to zero before repeating the same cycle, the current which flows out of the generator will be pulsed. | true. |
| T/F: Induction motors rely on the principle of self-induction in order to operate. | False: rely on mutual induction |
| T/F: the current which flows out from a DC generator will always flow the same direction. | true. |
| Current can only pass through the valve tube when what occurs? | when the cathode is negative and the anode is positive |
| what is the third form in the transformer law? | Is/Ip = Vp/Vs |
| how are the components different from an induction motor and a conventional motor? | in a conventional motor there is a armature and a magnet. In the induction motor, the magnet is replaced by the stator; and the armature is replaced by the rotor |
| What are the 3 types of transformers? | *open-core/air-core *closed core *shell |
| Which type of transformer is the highly efficient and is used in xray equipment? | shell type |
| What device has a single core surrounded by a single coil? | an autotransformer |
| For an autotransformer, if you use all the taps on the primary side but fewer on the secondary side what type of transformer are you using? | step down transformer |
| What device is used in xray equipment to maintain a steady source voltage, supply current to the high voltage transformer, provide voltage and current to filaments of the tube and time circuit? | an autotransformer |
| T/F: in autotransformers, no matter where the primary voltage is applied this is a magnetic field regardless and will still extend thru the core and induce a current in the secondary. | true |
| What type of transformer is high voltage and is currently used today? | shell type |
| The transformer that provides the high voltage required for xray exposures operates on what type of current? | AC |
| What is the process of rectification? | converting the AC signal from the high voltage that is supplied to make xray exposures into a pulsating DC signal for the tube to be useful. |
| What was used before valve tubes were used in the process of rectification? | the xray tube itself. this was self-rectification. however, it resulted in shorter tube life. |
| When valve tubes were used what was the result? | half wave rectification; it eliminated part of the AC pulse but only had half of the pulsating DC. |
| Autotransformers are what kind of device? | self-induction |
| Transformers are what kind of device? | mutual-induction |
| What were used after valve tubes? | solid state rectifiers |
| What are the 2 main types of semi-conductors in solid state rectifiers? | *N-type *P-type |
| What is on the N-type side? | loosely bound outershell e-; they can be easily moved |
| What is on the P-type side? | positive "traps" or "holes" that will accept e-; unfilled orbitals |
| What is the PN junction? | where the two materials are connected; works just like a valve tube. |
| What happens when a negative charge is applied to the N-type material? | the loosely bound e- will be attracted to the P-type side where the "holes" are and pass through the junction. Causing there to be an e- flow. |
| What happens when a positive charge is applied to the N-type material? | There will be no e- flow because the loosely bound e- will want to repel the P-type side because it is now negative and be more attracted to the N-type side which is now positive. |
| What is an example of a diode? | the xray tube |
| So after the discovery of solid state rectifiers, what was the end result of converting AC into pulsating DC current? | full wave rectification |
| Why is half wave rectification not efficient? | it wastes half of the electrical energy; if the other half of the AC current could be utilized, higher potential could be applied to the tube for longer periods of time. |
Created by:
mokapis
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