Qualification > Sciences
Physics Help HERE ONLY !!
annie_angel:
--- Quote from: Shogun on May 26, 2009, 04:01:23 pm ---
--- Quote from: annie_angel on May 26, 2009, 03:41:33 pm ---can anyone help wid the time base control ; base emitter collector and how the resistance works?? ??? ???
--- End quote ---
the time base system works for the x plates on the cathode ray osclliscope(CRO), the thing is tht, dpending on time the voltage goes zero between the plates then after acertan period of time say 0.5 secs the voltage gose up to its original value, how does this help? the x plate is ment to let the beams of electrons move horizonataly (left and right) so it hits the screen (on both the left and right side). so to do this, lets say abeam of elctrones in an CRO is coming and as it passes through the x plates(which is charged with postive and negative charge) the beam of electron (which is negative in charge) deflects towards the postive charge plates.
lets say the positive plate is aranged on the right, so when thier is voltage the beam deflects to the right after CERTAIN SET TIME the voltage goes zero (so no charged plate) and the beam returns to its original path (i.e the left side) then again after a certain set time the voltage goes up and the beam of electrons deflects to the right again.. so this is how the beam moves right and left with the help of x plates whic is TIME BASE system.
base emiter stuff...
the base and emmiter and collector wires are used in a transistor. the for the lamp to work (which is uually placed on the path of colletor emitter path) there must be a current on the base current and there must be a suitable potential difference of 0.6v across the base emitter path.
these conditions are needed for the transistor to work which acts as an automatic switch to switch on the lamp (which is usually placed in the collector -emitter path)
resistance stuff,
they say to the current "get the hell outta here" , u see they act as aopposition to the flow of current in the circuit, it does not let the current to pass through. it blocks the path of the current. with variable resistor u can change the amount of blockage, which means u can allow certain ammount of current to pass and flow through.
any more help or confusion or difficulties,plz do ask me.
--- End quote ---
THANK U SO MUCH!!!these r actually da simplest meaning for me...:D...+rep
Shogun:
ure welcome
zara:
hi eveyone...
i need help with CRO....
esp the calibration part....n ven they ask how these graphs are produced by the CRO...
i hv no clue to it ???
sweetsh:
A particular question would be great zara.
Shogun:
hey this is how cro works i explained it throughly
cathode ray oscillascope. has 6 parts.
the filament: it goes through thermionic emiision(where a substance is heated it releases electrons) this filament is heated and releases electorns with negative charge.
the anode grid: it has a positve charge. this controls the nrightness (ill tell u how later)
the cathode grid: it has a negative charge, this allows the beam of electron (the electrons emitted when tht filament was heated)
the y plates:hese have plates with (+) and (-) charge and are attached vertically to each other on the tube of the CRO. this helps the beam of electrons move up and down so the beam of electrons spread evenly (up and down) on the screen.
the x plate: these have plates with (+) and (-) charge and are attached horizontilly to each other on the tube of the CRO. these help the electrons move (left and right) as it hits the screen.
the screen: at the end of the CRO is the screen (made of fluroscent usually) when electorns hit this screen it glows.
without x plate and y plates u will see the beam of electrons hitting one point of the screen only (so only tht part glows) for eg:on TV (just an example) , if with out x plates and y plates, picture can only be seen as a spot of light (picture) on the screen. but with x and y plates the electrons are able to reach both (up and down) and (right and left) with the help of y plates and x plates respectively. (ill tell u how they work later))
how does the OCR work?
first the filament is heated, beams of electrons are emitted (this is callerd thermionic emission). they go throu the cathode. what does cathod do? Cathode are negatively charge (-) and so are the beam of electrons, so repulsion take place due to similar charges allowing some beams of electrons to "stay back". This control the brightness cuz "the more number of electrons hittin the screen, the brighter the pic comes on the screen". ok, then the beams pass through the anode. what does the anode do? Anode is positively charged (+) and the beam of electrons are oppesitely charged. this anode atracts the beam of electron giving the "boost" or "acceleration" and to travel in a straight line (beam). then it reaches the Y plates. as i told u the help the electrons move up and down . they are plates with voltages (charged with (+) and (-))). they are GIVEN WITH A.C VLTAGE because if it was D.C then the elctrons would only move up OR down depending on the position of the positively charged plate ( as beam of electron is negatively charged). u see, A.C current changes its direction so the plates change their charges, whic means (+) become (-) then later (-) becomes (+). so (+) charge changes its positon and so does the beam of electron which changes its direction of deflection. this helps the electrons to touch both up and down of the screen.
the X plate are same, except they help the electrons to move right and left they are also charged except tht they are aranged horizontally. they are time base. the work with time, how? by letting the voltage between these plates go 0 then after sometime go to a certain value. how tghis helps? as the voltage has acertain value thts not 0 the beam deflects to towards positively charged plate. then when after a certain time it the voltage goes 0 immediately. this all ows the beam of electrons to GO BACK its old path (which was before deflection at X PLATE), then vise versa. this helps the electrons go left and right on the screen.
U might ask what in x plate there is time base and in y plates are AC current? why cant the put AC on the xplates too? This is because i think tht the time base system helps beam to go in the REQUIRED or aprropriate horizontal path.
then finally the electrons reaches the screen in every direction (with the help of x and y plates) which causes the whole fluroscent screen to glow or lit.
however i donthink we have any calibrations or how does it show them as graph explainations in our syllabus..
any help needed or any confusion im all here m8....
i hope this helpd
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