Physics: Post your doubts here!

[confused123]

Accuracy and Precision?

?
Accuracy is when the measured value is closer to the actual value such as speed of sound in air is 330 m/s. if you come up with a measurement closer to it then its accurate. if u draw a graph there should be sharp peak closer to actual value.
precision is when measurements are close enough to the mean of all the measurements taken. the graph is spread evenly around the mean value. all measurements have a very less difference from the mean value. if a measurement is precise it doesn't mean it has to be accurate as well.

correct me if m wrong. tnx

 

[hassam]

can somebody tell me..a situation where resonance is useful and one where its is harmful....pls write a expplained sentence....

 

[smzimran]

can somebody tell me..a situation where resonance is useful and one where its is harmful....pls write a expplained sentence....

Aoa wr wb,
Harmful:
The operation of the engine of a vehicle causes a periodic force on the parts of the vehicle, which can cause them to resonate. For example, at particular frequencies of rotation of the engine, the mirrors may resonate. To prevent excessive vibration, the mountings of the mirrors provide damping.

Useful:
Musical instruments rely on resonance to amplify the sound produced.The sound from a tuning fork is louder when it is held over a tube of just the right length, so that the column of air resonates.

 

[smartangel]

http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_w07_qp_4.pdf
Q11 a. why is a country divided into a number of cells?

 

[smartangel]

also, 11 a (ii) of this paper http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s08_qp_4.pdf

 

[smzimran]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w07_qp_4.pdf
Q11 a. why is a country divided into a number of cells?

Aoa,
See the application booklet page 41-42

 

[smzimran]

also, 11 a (ii) of this paper http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s08_qp_4.pdf

There is no 11(a)(ii) !
if u r talking abt part (b) i would advise you to learn the answer frm the m.s
this question has been repeated many times!

 

[smartangel]

There is no 11(a)(ii) !
if u r talking abt part (b) i would advise you to learn the answer frm the m.s
this question has been repeated many times!

there is Q11 a (ii) :S June 08 paper 4. http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s08_qp_4.pdf

 

[smzimran]

there is Q11 a (ii) :S June 08 paper 4. http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s08_qp_4.pdf

Oh, ok!
Here goes:
1. the amplitude:
In FM modulation, amplitude is unchanged and it will be the same amplitude of carrier wave, which is 6.0 V
So, variation of amplitude = 0

2. the frequency:
frequency variation = frequency deviation of the carrier wave * amplitude of information signal
frequency variation = 20 * 1.5 = 30 kHz

frequency of carrier wave was 500 kHz
Limits = (500 - 30)kHz and (500 + 30)kHz
= 470 kHz and 530 kHz

This change between frequencies (470 kHz and 530 kHz) happens 8000 times in one second [frequency of information signal = 8 kHz]

 

[smartangel]

in Q 11 b(ii)..how do we calculate the frequency of the information signal?
http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_w09_qp_42.pdf

 

[sweetiepie]

HOPE THIS HELPS EVRYONE

 

[hmlahori]

No, it isn't related to Centripetal force - you're not expected to know about it in an AS Level paper. B should be the answer, because that is the resultant of normal force and friction force on the tyre. Force of friction is in the same direction as car's motion because the tyre must be rotating in a clockwise direction.

Ohh ok i get it now thanks!

 

[XPFMember]

june 2002 q4b) at max displacement the p.e is maximum. and at mean position it is zero. so the graph will be at max at max displacement. but it will be all above xaxis because energy can not be negative.
c) t = 2pie * sqr root of mass / sqr root of 'k'
when mass decreases time period also decrease.
sorry i dont knw abt amplitude

aoa
is it like a full wave rectification graph..? right?

 

[XPFMember]

nov 2002) when 1/2 f0 is impressed then the time period will be 2T. so every impulse is after 2 oscillations. means alternate oscillations are energized. so there is continuous increase of amplitude at every impulse.

What exactly am I supposed to write? :s do i write this all ^

 

[raamish]

How do we do these questions?
Qs 24 and 27
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s06_qp_1.pdf

Qs 23, 26
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s07_qp_1.pdf

Qs 26,27,28
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s08_qp_1.pdf

Qs 27
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_w06_qp_1.pdf

Qs 23,24,25
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_w07_qp_1.pdf

 

[confused123]

How do we do these questions?
Qs 24 and 27
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s06_qp_1.pdf

Qs 23, 26
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s07_qp_1.pdf

Qs 26,27,28
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s08_qp_1.pdf

Qs 27
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w06_qp_1.pdf

Qs 23,24,25
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w07_qp_1.pdf

q.24) Intensity directly proporitonal to Amplitude sq. , so 2I direct propo to A^2 , put A^2 instead of I in the place of in 2I.

Now under root 2A^2 = A^2 = 1.4A , frequency halved means half the number of waves will be created. so B


27) more lines or slits per meter so diffraction will increase and the angle between 1st nd 2nd will increase but less numbers of orders will be visible as more diffraction taking place. distance increases between adjacent maximas and minimas. i am not so sure about this explanation.

 

[raamish]

q.24) Intensity directly proporitonal to Amplitude sq. , so 2I direct propo to A^2 , put A^2 instead of I in the place of in 2I.

Now under root 2A^2 = A^2 = 1.4A , frequency halved means half the number of waves will be created. so B


27) more lines or slits per meter so diffraction will increase and the angle between 1st nd 2nd will increase but less numbers of orders will be visible as more diffraction taking place. distance increases between adjacent maximas and minimas. i am not so sure about this explanation.

When u have time plzzz do the rest of the questions

 

[confused123]

How do we do these questions?
Qs 24 and 27
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s06_qp_1.pdf

Qs 23, 26
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s07_qp_1.pdf

Qs 26,27,28
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s08_qp_1.pdf

Qs 27
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w06_qp_1.pdf

Qs 23,24,25
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w07_qp_1.pdf

s07) 23) P is showing us the amplitude as it is a displacement time graph. the displacement at Q can't always be zero as the particle will oscillate upwards and downwards it will not stay stationary. Energy at point R also involves potential energy. so we are only left with option D which has to be CORRECT!

26) i think its D because decreasing wavelngth will result in increase in separation of fringes. Lambda = ax / d

s08) the distance is doubled so amplitude will be halved...rest later

 

[confused123]

s08 27) frequency = velocity over lambda , x is the distance from the wall where a antinode forms. 4 consecutive antinodes will make one wavelength so F = v/ 4x D ans.

28) d sin Q = n lambda , d= 1/N , sin Q = 3 lambda as its the 3rd order into lambda into N , i.e B option .

w06) 27) i don't know.

w07) 23. idk
24) lambda = ax /d , so increasing wavelength will increase the fringe separation as well. D option
25) idk

 

[unique840]

aoa
is it like a full wave rectification graph..? right?

yup