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[WARRIOR]

ans10b)
see if we want to change the temperature at which the lamp switches on, we have to change the value of resistance R1. if we increase the value of the resistance then more voltage will flow through the transistor and if we decrease the voltage then less voltage will flow through the transistor. therefore if we assume that the amount of heat falling on the thermistor is constant then when we increase or decrease the value of R1 so will the value of the voltage passing through the tranistor will change. so if we want to make the lamp switch on at a different temperature we change the value of R1 because if the heat is falling on the thermistor and thus its resistance decreasing then if the base voltage is enough to switch on the transistor it will light however decreasing the value of the resistor R1 will cause the voltage flowing through the transistor to be too less to switch it on (this is if we want to make the temperature at which the lamp lights more; just explain the opposite thing if u want the temperature at which the transistor lights lower than it is and also u dnt need to expalin all this, ive done this to help u understand it and if u want a shortened version ill be happy to help). therefore in short the temperature at which the lamp lights can be changed by changing the value of R1. (the lamp lights when the base voltage becomes enough for the lamp to switch on)

hmm llook how i thought of it and tell me if its right or wrong


When Temp is high n the thermistor its resistance  decreases... therefore the resistance accruse teh base and emittor is high enough  to switch on the transistor  and therfore lamp is on

If thermitor has low voltage thn  the normal resisor has high voltage.( lets say total voltage is 10 )  so if u increase the resistance  of the varable resistor from x to x ..it will get more voltage..and so there will be less voltage for the thermistor ..and so heat wil have to decrease it by less amount ! to get to a low resistance where low voltage 
makes sence? nope.

[WARRIOR]

wait a minute

why does the value of R1 affect the voltage of the transistor..? why not the theristor ?

crap im confused

[Ghost Of Highbury]

wait a minute

why does the value of R1 affect the voltage of the transistor..? why not the theristor ?

crap im confused

If we want the lamp to switch on at a different temperature, say higher temperature.

The normal heat on the transistor reduces the resistance of the thermistor, thus more voltage flows through the transistor and switches on the lamp.

HOWEVER, we dont want the lamp to switch on because of normal heat, wen need higher temp. to switch it on, what to do we do??

for this, we need to decrease the resistance of R1, which allows more voltage to flow through R1, thus reducing the voltage flowing through the transistor. For more voltage to flow through the transistor again, a higher temperature (more heat )  will be required which will reduce the resistance of the thermistor further, and thus the lamp will switch on again.

[WARRIOR]

If we want the lamp to switch on at a different temperature, say higher temperature.

The normal heat on the transistor reduces the resistance of the thermistor, thus more voltage flows through the transistor and switches on the lamp.

HOWEVER, we dont want the lamp to switch on because of normal heat, wen need higher temp. to switch it on, what to do we do??

for this, we need to decrease the resistance of R1, which allows more voltage to flow through R1, thus reducing the voltage flowing through the transistor. For more voltage to flow through the transistor again, a higher temperature (more heat )  will be required which will reduce the resistance of the thermistor further, and thus the lamp will switch on again.

i got i got it now
 but if teh resistance of R1 i low doesnt it mean less voltage goes to it?

[Ghost Of Highbury]

i got i got it now
 but if teh resistance of R1 i low doesnt it mean less voltage goes to it?

Decreasing the resistance will allow more current to pass through it thus decreasing the voltage at the thermistor.

[guMnam]

sry if i m repeating...but i m confused with potential divider...can some one explain its working...in tuning on a transistor...Thanks in advance:D

[astarmathsandphysics]

potential divider divides voltage in ratio of resistances.
eg 12V with an output resistance of 4ohm and circuit resistance of 2 ohm
output voltage=4/(4+2)*12=8V

[WARRIOR]

potential divider divides voltage in ratio of resistances.
eg 12V with an output resistance of 4ohm and circuit resistance of 2 ohm
output voltage=4/(4+2)*12=8V

does it matter where the lamp is?

to the right of the thermistor or to the right of the normal resistor?

[guMnam]

potential divider divides voltage in ratio of resistances.
eg 12V with an output resistance of 4ohm and circuit resistance of 2 ohm
output voltage=4/(4+2)*12=8V

sry i didnt get it...can u elaborate

[ambitious94]

Hi,
I'm new to the forum, and found this thread rlly helpful. Man, some of u r rlly smart and very helpful too!
I have a couple of questions that i found trouble with while solving in the past papers. All these questions are mainly from Nov 07 (Ppr 3)

1) How do u draw a diagram to represent a sound wave or a longitudinal wave? I usually draw vertical lines with spacings for compressions and rarefactions, is that correct? How would you mark the wavelength on it?

2) Secondly, in electromagnetic induction, wat is more appropriate to say: am e.m.f is induced, or a current, or a voltage? :S

3) How many cms of Al sheets would be required to completely block B-particles from a source?

4) In Nov 07, can anyone please explain how to draw the logic gates, and why!! I thought abt making it a NAND gate, but it was wrong. What's your theory abt this?

Thanks in advance

[guMnam]

Hi,
I'm new to the forum, and found this thread rlly helpful. Man, some of u r rlly smart and very helpful too!
I have a couple of questions that i found trouble with while solving in the past papers. All these questions are mainly from Nov 07 (Ppr 3)

1) How do u draw a diagram to represent a sound wave or a longitudinal wave? I usually draw vertical lines with spacings for compressions and rarefactions, is that correct? How would you mark the wavelength on it?

2) Secondly, in electromagnetic induction, wat is more appropriate to say: am e.m.f is induced, or a current, or a voltage? :S

3) How many cms of Al sheets would be required to completely block B-particles from a source?

4) In Nov 07, can anyone please explain how to draw the logic gates, and why!! I thought abt making it a NAND gate, but it was wrong. What's your theory abt this?

Thanks in advance

actually u can use both emf and voltage but voltage is beter

[Ghost Of Highbury]

Hi,
I'm new to the forum, and found this thread rlly helpful. Man, some of u r rlly smart and very helpful too!
I have a couple of questions that i found trouble with while solving in the past papers. All these questions are mainly from Nov 07 (Ppr 3)

1) How do u draw a diagram to represent a sound wave or a longitudinal wave? I usually draw vertical lines with spacings for compressions and rarefactions, is that correct? How would you mark the wavelength on it?

2) Secondly, in electromagnetic induction, wat is more appropriate to say: am e.m.f is induced, or a current, or a voltage? :S

3) How many cms of Al sheets would be required to completely block B-particles from a source?

4) In Nov 07, can anyone please explain how to draw the logic gates, and why!! I thought abt making it a NAND gate, but it was wrong. What's your theory abt this?

Thanks in advance

http://www.antonine-education.co.uk/Physics%20A%20level/Unit_2/Waves/Progressive_Waves/wav_9.gif

[WARRIOR]

If we want the lamp to switch on at a different temperature, say higher temperature.

The normal heat on the transistor reduces the resistance of the thermistor, thus more voltage flows through the transistor and switches on the lamp.

HOWEVER, we dont want the lamp to switch on because of normal heat, wen need higher temp. to switch it on, what to do we do??

for this, we need to decrease the resistance of R1, which allows more voltage to flow through R1, thus reducing the voltage flowing through the transistor. For more voltage to flow through the transistor again, a higher temperature (more heat )  will be required which will reduce the resistance of the thermistor further, and thus the lamp will switch on again.

oki doki thanks man ! i understood it ..my concept was wrogn but i used to goet right asnwers for some reason .. now that i understand it <3 cheers + rep !

[ambitious94]

actually u can use both emf and voltage but voltage is beter

thanks

[guMnam]

thanks

anetyme mate:D