# A2 Physics | Post your doubts here

#### smzimran

We have to clear this solution cz its a main point in the syllabus.
(b) Candidates should be able to recall that a carrier wave, amplitude modulated by a single audio
frequency, is equivalent to the carrier wave frequency together with two sideband frequencies.
Here's what the textbook says on this matter:

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#### ousamah112

AOA.. That two points mean that when reflected ultrasound is received by the probe the successive compression and rarefaction of ultrasound wave causes the crystal to vibrate. Such that the positive and negative no longer coincides and crystals vibrate, as a result a voltage is produced . which is thn amplified and fed to an c.r.o.
it is just like how a microphone works.

#### ali2012

can anybody explain Qs 3b/1 and 2 of p-43 oct/nov.plz .i think there is a problem with ms regarding this qs!

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#### ousamah112

work done= pressure x change in volume
change in volume= (2.1 x 10^3 x 10^-6)-(1.8 x 10^3 x 10^-6)
w.d= 1.o x 10^5 x change in volume..

dont forget to change cm(cube) to metre(cube)!

#### Mustehssun Iqbal

work done= pressure x change in volume
change in volume= (2.1 x 10^3 x 10^-6)-(1.8 x 10^3 x 10^-6)
w.d= 1.o x 10^5 x change in volume..

dont forget to change cm(cube) to metre(cube)!
how do you know the pressure?? Isn't the pressure going to be atmospheric pressure + pressure exerted on the gas??
thanks

#### hassam

how do you know the pressure?? Isn't the pressure going to be atmospheric pressure + pressure exerted on the gas??
thanks
well in derving work done = p delta v....we assumed the gas expanding or contracting against constant external pressure....chek chapter 4 chriss mee book for frther clarification

#### hassam

practice question LAST PART TOUGH ONE !!!

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#### ousamah112

how do you know the pressure?? Isn't the pressure going to be atmospheric pressure + pressure exerted on the gas??
thanks
yes..pressure is considered to be constant.

#### maybeitwasnoone

Its said that plate P is earthed which means its at zero volts. And The Gravitational Force is acting downwards on the Oil droplet, the opposite force therefore is upwards since its stationary. Since Plate P is at zero, Plate Q has to be positive and since there is an attractive force acting upwards to keep the oil droplet stationary, it has to be negative.

#### smartangel

Its said that plate P is earthed which means its at zero volts. And The Gravitational Force is acting downwards on the Oil droplet, the opposite force therefore is upwards since its stationary. Since Plate P is at zero, Plate Q has to be positive and since there is an attractive force acting upwards to keep the oil droplet stationary, it has to be negative.
thanks..could you help me with Q3 b ii part 1..how to find amplitude? http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w08_qp_4.pdf

#### ali2012

stuck in qs 3b/1,2 /nov 2010 p-43.help needed