ALL PHYSICS DOUBTS - POST HERE !!

[holtadit]

Thanks Kimo.

Anyone with a DEFINITE answer as to whether my above answer is correct/wrong.

[guMnam]

Okay.

There is low heat on the thermistor.

SO  Its resistance RISES

P.D. across thermistor RISES

As the Resistance of R₁ is LESS THAN the resistance of the THERMISTOR  the Voltage output to the Transistor is LARGER than 0.6V.

So the transistor switches on and the lamp lights.

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Would this get me 3 marks ? Is the explanation correct ? Its from summer 2007 paper 3 Question 10

i dont effing get it....c the thing needed to switch on the transistor is...tht one of the resistors in the potenial divider has to be more and the other has to be less than tht of the pd of the circuit??? is it like tht

[Fastal]

i dont effing get it....c the thing needed to switch on the resistor is...tht one of the resistors in the potenial divider has to be more and the other has to be less than tht of the pd of the circuit??? is it like tht

i dont understand this either.

[NidZ- Hero]

can any one help me wid 2004 m/j p3 phy Q2 (c) can ny one tell me wats de rght answer 4 this  :)answer thanzed?:p

[WARRIOR]

i dont effing get it....c the thing needed to switch on the transistor is...tht one of the resistors in the potenial divider has to be more and the other has to be less than tht of the pd of the circuit??? is it like tht

My teacher was a examiner and used to correct  exams of igcse . she told me to rwright this any time it comes up ( transistor ) no matter The reading  resistance of LDR or thermister you say the following (  if its increase right increase if its dec right dec )
in this case an LDR WITH LIGHT . ( and it says the bulb switches on )
So light decreases ristance of thermistor . Voltage acros base and emimitor is high enough to swtich transistor on and bulb lights
another case:
thermistort without heat . ( and it says fire alarm is off )
so thermistor has high resistance , voltage acrose base and emmitor is nto hight enough to switch transistor on and bulb doesnt light


get my point?

[guMnam]

can any one help me wid 2004 m/j p3 phy Q2 (c) can ny one tell me wats de rght answer 4 this  :)answer thanzed?:p

the kinetic energy of the rok decreases...some of it is transformed into sound of splash...sum of it makes the water move ..and some of it is still there ans it is sink in the water..

[holtadit]

can any one help me wid 2004 m/j p3 phy Q2 (c) can ny one tell me wats de rght answer 4 this  :)answer thanzed?:p

Okay when you drop a rock in water what happens ? You HEAR a splash. So sound energy is one answer.

Next, all energy EVENTUALLY lands up as HEAT. SO ALWAYS write heat energy. That should be enough for 2 marks.

You remind me of Nid.  

[guMnam]

My teacher was a examiner and used to correct  exams of igcse . she told me to rwright this any time it comes up ( transistor ) no matter The reading  resistance of LDR or thermister you say the following (  if its increase right increase if its dec right dec )
in this case an LDR WITH LIGHT . ( and it says the bulb switches on )
So light decreases ristance of thermistor . Voltage acros base and emimitor is high enough to swtich transistor on and bulb lights
another case:
thermistort without heat . ( and it says fire alarm is off )
so thermistor has high resistance , voltage acrose base and emmitor is nto hight enough to switch transistor on and bulb doesnt light


get my point?

yea i get tht part the only thing i dont uderstand is the relation between th two resistor..one of the is thermistor in our case...yea just fill in this for me.. in order to turn on the transistor the resistance of the thermistor should be______ and the resistance of the2nd  resistor is ________. this makes the voltage across the base and emitor high enough to turn the transistor on..options ...high and low

[WARRIOR]

yea i get tht part the only thing i dont uderstand is the relation between th two resistor..one of the is thermistor in our case...yea just fill in this for me.. in order to turn on the transistor the resistance of the thermistor should be______ and the resistance of the2nd  resistor is ________. this makes the voltage across the base and emitor high enough to turn the transistor on..options ...high and low

it doesnt matter what it is..if the resistance of thermister r or high or low it doesnt matter. as logn as bulb is on ...that means there is enough voltage . and the resistance of teh second resstance does not affect anythign !! unless if tehre is a variable resistor !!
 check may june 2007  question 10 ..varible resistor part

man im gonna stop advising you about this topic caz i dunno anythin about it i jsut learnt it by heart!

[guMnam]

it doesnt matter what it is..if the resistance of thermister r or high or low it doesnt matter. as logn as bulb is on ...that means there is enough voltage . and the resistance of teh second resstance does not affect anythign !! unless if tehre is a variable resistor !!
 check may june 2007  question 10 ..varible resistor part

man im gonna stop advising you about this topic caz i dunno anythin about it i jsut learnt it by heart!

hmmm....okay can u tell me if in a series combined resistance of two resister is...r1+r2.....yani if r1 is 2o and r2 is 1o..the combined resistance would be 3..or 1

[holtadit]

See the picture.

Click on it to enlarge.

[WARRIOR]

hmmm....okay can u tell me if in a series combined resistance of two resister is...r1+r2.....yani if r1 is 2o and r2 is 1o..the combined resistance would be 3..or 1

3...in series you jsut add up all teh resistance


in parallel you always use the formula  1/tot. resitace = 1/r + 1/r and then invert the asnwer !

for example if resitos in apralel were 3 and 5

1/3 + 1/5  = 1/r

asnwer will be 15/8 ( invert )  and so 1.875 is the total resistance

[WARRIOR]

See the picture.

Click on it to enlarge.

caz when the water is being pumped up ! there is friction between the walls and water and so some energy will be lost and therrfore you need more kinetic enrgy to pump uup the water ( TO COMPENSATE FOR THE LOST ENERGY )

[NidZ- Hero]

Okay when you drop a rock in water what happens ? You HEAR a splash. So sound energy is one answer.

Next, all energy EVENTUALLY lands up as HEAT. SO ALWAYS write heat energy. That should be enough for 2 marks.

You remind me of Nid.  

oye but its 4 3 marks

[holtadit]

oye but its 4 3 marks

I suggest reading the MS.