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Author Topic: ALL PHYSICS DOUBTS - POST HERE !!  (Read 228981 times)

Offline Ghost Of Highbury

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1050 on: May 24, 2010, 03:29:30 pm »
Quote from: Mr.DitD on May 24, 2010, 03:17:21 pm
Hello everyone!!

If there is only one things i do not understand in the whole school syllabus it's the TRANSISTOR. So can someone please explain the transister in detail and say how it works exactly. If you use a diagram or example it would really help.

In the book I have it only says: If there is a current in the base and collecter then there is a current in emitter. HOWEVER, my teacher says it has nothing to do with current, and if the potential difference between the base and emitter is more than 0.7 then there is a current in collecter.  ??? ??? ???

Please help!!!!!!!


Its best if u understand the transistor circuits with thermistors and varying resistance...wait for 5 minutes..ill draw the diagrams and write the explanation.
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Offline Ghost Of Highbury

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1051 on: May 24, 2010, 03:43:20 pm »
Quote from: A@di on May 24, 2010, 03:29:30 pm

Its best if u understand the transistor circuits with thermistors and varying resistance...wait for 5 minutes..ill draw the diagrams and write the explanation.

Ok attached.

EDIT : "0.6V" not "06V"
« Last Edit: May 24, 2010, 03:52:44 pm by A@di »
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Offline WARRIOR

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1052 on: May 24, 2010, 03:47:09 pm »
Quote from: A@di on May 24, 2010, 03:43:20 pm
Ok attached.

umm i think its wrong

THE VOLATAGE ACCROSS THE VARIABLE RESISTOR SHOULD BE HIGH SO THE VOLTAGE ACCORSE B-E HIGH TOO RIGHT?
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Offline Ghost Of Highbury

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1053 on: May 24, 2010, 03:52:02 pm »
Thats exactly wat i said. My IGCSE book says the same thing, im pretty sure this isnt wrong.
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Offline Mr.DitD

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1054 on: May 24, 2010, 03:58:26 pm »
Quote from: A@di on May 24, 2010, 03:43:20 pm
Ok attached.

EDIT : "0.6V" not "06V"

Thanks. But im still confused. The resistance of thermistor decreases when there is heat*.
I didnt understand what u mean by share of Voltage, does it mean the voltage across it.

So in this case when there is low temp, resistance of thermistor increases. As a result, will there be higher OR lower voltage across thermistor?!?!
And if the voltage across thermistor increases, will there be a lower voltage in the variable resistor, which means Vbe will be high??!?!
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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1055 on: May 24, 2010, 03:59:06 pm »
Quote from: A@di on May 24, 2010, 03:52:02 pm
Thats exactly wat i said. My IGCSE book says the same thing, im pretty sure this isnt wrong.

when resistance of teh thermistor decreases..doesnt it get less voltage???

and therefore the variable resistor gets more voltage

and therefore the voltage accors teh base emiitor is high?
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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1056 on: May 24, 2010, 04:00:19 pm »
Quote from: Mr.DitD on May 24, 2010, 03:58:26 pm
Thanks. But im still confused. The resistance of thermistor decreases when there is heat*.
I didnt understand what u mean by share of Voltage, does it mean the voltage across it.

So in this case when there is low temp, resistance of thermistor increases. As a result, will there be higher OR lower voltage across thermistor?!?!
And if the voltage across thermistor increases, will there be a lower voltage in the variable resistor, which means Vbe will be high??!?!

thats exactly what im asking !! By the way HIGH TEMP DECREASES THE RESISTANCE OF THERMISTOR
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holtadit

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1057 on: May 24, 2010, 04:00:32 pm »
R1 should be LESS than R2 for the Voltage output to BE HIGH.


Hence, the thermistor should have a lower resistance (example when heated) than the VARIABLE resistor in order for the V output to the transistor to EXCEED 0.6 V and hence trigger the transistor.
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Offline Ghost Of Highbury

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1058 on: May 24, 2010, 04:02:59 pm »
Quote from: Kimo Jesus on May 24, 2010, 03:59:06 pm
when resistance of teh thermistor decreases..doesnt it get less voltage???

and therefore the variable resistor gets more voltage

and therefore the voltage accors teh base emiitor is high?

High temperature - Less resistance k? V = I*R. when R decreases, V decreases. Thus, it gets less voltage and the Variable resistor side gets more voltage.
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holtadit

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1059 on: May 24, 2010, 04:03:56 pm »
@   A@di


What I said does it make sense ??
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Offline Ghost Of Highbury

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1060 on: May 24, 2010, 04:05:43 pm »
Quote from: Ari Ben Canaan on May 24, 2010, 04:00:32 pm
R1 should be LESS than R2 for the Voltage output to BE HIGH.


Hence, the thermistor should have a lower resistance (example when heated) than the VARIABLE resistor in order for the V output to the transistor to EXCEED 0.6 V and hence trigger the transistor.

Yes, thats exactly wat i said. Whats the confusion about?

applying V-I*R, when R decreases (thermistor), the Voltage decreases. So, the other part, Vbe , the variable resistor part gets more voltage, and if V>0.6V is flowing throught the emitter of the transistor, the transistor switches on.
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Offline Mr.DitD

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1061 on: May 24, 2010, 04:06:07 pm »
Quote from: Ari Ben Canaan on May 24, 2010, 04:00:32 pm
R1 should be LESS than R2 for the Voltage output to BE HIGH.


Hence, the thermistor should have a lower resistance (example when heated) than the VARIABLE resistor in order for the V output to the transistor to EXCEED 0.6 V and hence trigger the transistor.

I think u're right. But what is exactly "voltage output"!?!?

I have a very big issue with voltage!!!  ???

By the way can someone please explain the general functioning of the transistors!?!?!
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Offline Ghost Of Highbury

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1062 on: May 24, 2010, 04:07:05 pm »
Quote from: Mr.DitD on May 24, 2010, 04:06:07 pm
I think u're right. But what is exactly "voltage output"!?!?

I have a very big issue with voltage!!!  ???

By the way can someone please explain the general functioning of the transistors!?!?!

The voltage in the emitter part of the transistor?
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holtadit

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1063 on: May 24, 2010, 04:07:56 pm »
Quote from: Mr.DitD on May 24, 2010, 04:06:07 pm
I think u're right. But what is exactly "voltage output"!?!?

I have a very big issue with voltage!!!  ???

By the way can someone please explain the general functioning of the transistors!?!?!

Dude, such questions are for three marks.

The MS gives three points - just memorise them; few days left to the exam and you have no other choice.
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Offline Malak

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Re: ALL PHYSICS DOUBTS - POST HERE !!
« Reply #1064 on: May 24, 2010, 04:08:15 pm »
http://www.freeexampapers.us/IGCSE/Physics/CIE/2006%20Nov/0625_w06_qp_1.pdf

Q15 Why is it D?

Q18 ans and Explaination

Q31 ans and Explaination

Thx :)

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