# A2 Physics | Post your doubts here

#### Zishi

ok a simple question distrubing me..
when the current is increasing from zero and moving towards the max. of curent aftr which the graph is still with no increase in current aftr it.

wel fr that time emf is increasing bt is increasing in in neagitve axis!!1
why nt in positive axis??

hope u gt what i am tryng to say
I guess you're talking about the third phase. The emf is zero in the second phase, after which it increase sharply to a positive constant value.

#### hassam

wel wat is the ans to this practise question ???
i have posted solution

I guess you're talking about the third phase. The emf is zero in the second phase, after which it increase sharply to a positive constant value.
I am talking abt the frst phase where the emf is increasing ...
can u explain why this is so??

i mean to say that why is it increasing from neagative value???
ehy nt frm positive value?

I am talking abt the frst phase where the emf is increasing ...
can u explain why this is so??
pease can u post the link??

#### SkyPilotage

I am talking abt the frst phase where the emf is increasing ...
can u explain why this is so??

i mean to say that why is it increasing from neagative value???
ehy nt frm positive value?
because E m f by lenz law is minus rate of change of flux!

#### hateexamz

Guyz i need help real bad my physics teacher has got mumps nd i have a lot ov past paper queries nd i mean it alot really does mean ALOT can anybody help...its a bit crowded here in this thread so anybody who is really gud in physics can help me in PM???

#### SkyPilotage

Guyz i need help real bad my physics teacher has got mumps nd i have a lot ov past paper queries nd i mean it alot really does mean ALOT can anybody help...its a bit crowded here in this thread so anybody who is really gud in physics can help me in PM???
just post it in here, much higher chance of answers in time and people can correct each other...
Dont worry , period of a day is 24 hours - 7 hours sleep - 2 hour food breaks - 3 hour fun breaks = 12 hours of pure study i.e 7 papers x 4 days = 28 papers ---> meaning you got time for finishing all the past papers and time for revision and relaxation !!! No need to Panic especially at this time !

#### SkyPilotage

Will start answering it in 30 minutes, hold on!

#### miss irfan

what are the factors which determine the frequency response and sharpness of the resonance.?
and the importance of critical damping in cases such as a car suspension system.

#### hassam

well car suspensions system are critcally damped to bring the car to equilibrium position in the shortest possible time without setting up oscillation which otherwise cud make it difficult to control the car

#### hassam

well thermocuple has a very small heat capacity as its temp. sensing probe is small so its very quick to respond and doesn't significantly alters the temp. of object being measured by absorbing heat......thermistor thermometer is very much sensitive bt over a short range.......thermocouple can be used to measure temp. difference between two points......variation of e.m.f with temp. is non linear so requires calibration.....range is very high......can be used to measure temp at small points cos of thin probe.....no power supply required ....well u myt have saw questions in AS in which thermistor is used in a potential divider circuit and by reading value on voltmetter we would give temp. of object.....so in those circuit diagrams ov corass there was a battery....bt in thermocouple no such thing

3ai)

we use the eq. x = Xo.sinwt fr calculating distance frm the mean position. when at time zero displace ment is zero.
means the initial co-ordinates of the graph should be (0,0) if we are using this formula.

similarly if the particle is at itx max. displacement frm mean position at time t=o

then we use x = Xo.coswt.

in the question the "x = Xo.coswt" is used. this shows that at amx. displacement (Xo) t is to be zero.

so put t = zero here u wil get d = 4.0 cos(220*o)

d = 4.0cm this is the max. displacement from mean position.
now fr finding total distance jxt multily it by 2 4.0 * 2 = 8.0 cm

as the particle is having 4.0 cm displacemnt above the mean and below the mean as well so the total dsitance it is traveling is 8cm

6a) power is calculated by p =I^2.R

so whatever the direction is of current it wil be squared to give a positive value so no effect is their for sinosidal curve
whether neagitve value or positve it wil be aquared as aaccording to frmula to give a positvie value

question 7 and 8 are a little more time taking (lendy) so skypilot wil surely tackle them.