plz, can u help in jun.08 Q4(c), and Jun.07 Q10 (b) need explanation for these questions. thanks.
okay so first june 07 q10 b--
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)
hope it helps
p.s. i think ive explained a bit too much though
okay now the second q--
see if the temperature increases so will the kinetic energy of the particles. therefore they will exert more pressure in the tube and therefore if the pressure increases the switch will switch on. this is because when we pressed the rubber cover the same thing was achieved but when there is a higher temperature it comes to the same thing
Note--when the transistor switches on it will in turn switch on the lamp
