Physics: Post your doubts here!

[usama321]

The Fly wheel has a small magnet of mass M mounted on it. Each time the magnet passes the coil, a voltage pulse is generated , which is passes to the c.r.o the display of the c.r.o is 10 cm wide . The flywheel is rotating at a rate of about 3000 revolutions per minute . Which time-base setting will display clearly separate pulses onscreen.

(some one please answer this question with explanation and from where can i learn about c.r.o as i can not find anything useful in book )

6000 revs per minute, that is 250 rev per second. As each revolution causes one pulse, just calculate the time for one pulse by 1/250 that is .004s. I can't give an exact answer but a time base of around 1 to 2ms should work.

 

[mehria]

MCQ QUESTIONS
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s08_qp_1.pdf

Q2,7,14,16,22,23,25,26,27,28,29,31,32

Please help with even one of these questions

22) from the end point of the limit of proportionality to Y we have elastic limit...after Y it'll be permanently deformed so frm X to Y it'll be elastic but not plastic

25) it is a very simple n easy question... as d is not the maximum displacement frm the mean position so it won't be the amplitude. it's just a displacement frm the mean position... for h-t graph one wavelength represents a time period while for s-d graph it will be a wavelength...

26) intensity is directly proportional to (amplitude)2 and inversely proportional to (distance)2 so in this question we will take (amplitude)2 inversely proportional to (distance)2... so by increasing r, A will decrease i.e. 1/r=8 so 1/2r=4 by doubling the r, Amplitude will be halved.

27) f=V/2l
V= speed and l= wavelength (x)
as from the node to antinode it is a half wavelength so full wavelength will be 2l
AND f=c/(2x2)l = c/4l

28) sinθ=nλ/d
for the third order of diffraction, wavelength = 3λ
d=1/N where N is the number of lines
so: sinθ=3λ / 1/N => sinθ=3λN

31) F=eV/d
as it's gaining 5 electrons so; e= (5) x (1.6 x 10^-19) = 8 x 10^-19
so F= (8 x 10^-19) x (5000) / (0.8 x 10^-2)= 5 x 10^-13 N
it is negatively charged so it will move upwards
remember to chnge cm into m........

 

[sudeep1097]

2) I upload a file watch page 4
7) accn of free fall on moon is aboutt 1/6 that of earth so, accn of free fall on moon is 1.6 m/s
so W=mass * accn of free fall
= 30 * 1.6 = 48 so about 49 N
14,16,22 Suchal Riaz ZaqZainab midha.ch usama321
23) Energy = 0.5*F*change in length..
=0.5*6*(40-70) (Convert it to meter) that is 0.03 = 0.09 J
25,26,27,28,31 Suchal Riaz ZaqZainab midha.ch usama321

29) Sin(θ) (which is basically the spacing divided by the distance)

So since sin(θ) = nλ/d

If λ is 1/2 and d is doubled the sin(θ) is reduced by 1/4

So 3.0mm/4 = 0.75mm

32) P=I^2*R

Power in Y = 0.5^2 * 2 = 1/2
Power in X= 1

1/2/1 = 1/2

16 is A:
because R is moving upwards and rightwards, we only need to consider rightwards as that makes the difference, because force is experienced towards right by the positive charge so moving upwards at 90 degrees doesn't make any difference in a uniform magnetic field. As positive charge moves towards direction of force the potential decreases as charges attract each other ( farther charges are more potential energy is present).

25 is B as p is not amplitude but just displacement and q is time period because graph is height against time.

26: D
We have I is directly proportional to A^2 and inversely proportional to x^2 so A^2 is inversely proportional to x ^ 2.
Hence, at P 8^2 is directly proportional to 1 / x^2 at Q A^2 is directly proportional to 1 / (2x)^2
Solving and removing proportionality sign we get (64/A^2) = 4 so A is 4.0 at Q.

31 is C :
E=V/D = 5000 / (0.8/100)
Now, electrostatic force (F) = q x E where q is charge of one electron.
But since the oil droplet has gained 5 electrons F = 5 x 1.6 x 10^-19 x E
and since it is negatively charged it is attracted towards positive that is upwards.

 

[Thought blocker]

16 is A:
because R is moving upwards and rightwards, we only need to consider rightwards as that makes the difference, because force is experienced towards right by the positive charge so moving upwards at 90 degrees doesn't make any difference in a uniform magnetic field. As positive charge moves towards direction of force the potential decreases as charges attract each other ( farther charges are more potential energy is present).

25 is B as p is not amplitude but just displacement and q is time period because graph is height against time.

26: D
We have I is directly proportional to A^2 and inversely proportional to x^2 so A^2 is inversely proportional to x ^ 2.
Hence, at P 8^2 is directly proportional to 1 / x^2 at Q A^2 is directly proportional to 1 / (2x)^2
Solving and removing proportionality sign we get (64/A^2) = 4 so A is 4.0 at Q.

31 is C :
E=V/D = 5000 / (0.8/100)
Now, electrostatic force (F) = q x E where q is charge of one electron.
But since the oil droplet has gained 5 electrons F = 5 x 1.6 x 10^-19 x E
and since it is negatively charged it is attracted towards positive that is upwards.

Genius mode activated ?

 

[yousef]

Hi ,
mass of gamma to be used is mass of electron , but how ? it should be as i guess 2* mass of electron as there are 2 moles

 

[Thought blocker]

The Fly wheel has a small magnet of mass M mounted on it. Each time the magnet passes the coil, a voltage pulse is generated , which is passes to the c.r.o the display of the c.r.o is 10 cm wide . The flywheel is rotating at a rate of about 3000 revolutions per minute . Which time-base setting will display clearly separate pulses onscreen.

It is been replied.

6000 revs per minute, that is 250 rev per second. As each revolution causes one pulse, just calculate the time for one pulse by 1/250 that is .004s. I can't give an exact answer but a time base of around 1 to 2ms should work.

 

[talha-_-khan]

6000 revs per minute, that is 250 rev per second. As each revolution causes one pulse, just calculate the time for one pulse by 1/250 that is .004s. I can't give an exact answer but a time base of around 1 to 2ms should work.

ITS 3000 Rev per min not 6000 and the answer in book is 10ms /cm

 

[Thought blocker]

ITS 3000 Rev per min not 6000 and the answer in book is 10ms /cm

usama321

 

[sudeep1097]

Genius mode activated ?

Haha did which i already knew!

 

[ZohaKhan]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s10_qp_41.pdf
Q.3 ...anyone?

 

[Thought blocker]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s10_qp_41.pdf
Q4 a)i and a)ii ???

usama321

 

[sitooon]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s10_qp_41.pdf
Q4 a)i and a)ii ???

Which paper is this !

 

[Thought blocker]

Which paper is this !

paper 4 A2

 

[sitooon]

paper 4 A2

No its not !

 

[Thought blocker]

No its not !

Yes its 5054 ??

 

[Thought blocker]

is it an alevel thread ?

Yes, check the heading. You are at wrong address

 

[mai jinn hun 2]

I cant understand the wording of this question.Is there anyone who can explain me the answer of this question?

 

[Hassan Ali Abid]

View attachment 38682I cant understand the wording of this question.Is there anyone who can explain me the answer of this question?

In a line spectrum you can see the lines ...each line shows an energy level which is infact a discrete energy level ie having a particular value.When an electron moves from the lower shell to a higher or vice virsa there's a change in energy and the energy change is also discrete, so these discrete energy changes provides the evidence that energy levels were discrete hence we came to know about the existence of discrete electron energy levels in the atom.

 

[sudeep1097]

B is in the wron

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s10_qp_41.pdf
Q.3 ...anyone?

I haven't studied O levels but i think these are the answers.
(i and ii) B is in the wrong drawer. As B has resistance 221 ohm.
I am hoping you can draw the circuit.
All the resistors have different values since they have tolerance and the voltmeter doesn't have infinite resistance while ammeter has some resistance.

 

[sudeep1097]

Hi ,
mass of gamma to be used is mass of electron , but how ? it should be as i guess 2* mass of electron as there are 2 moles

Gamma particles have no mass and that 2 means 2 gamma particles not 2 moles gamma particles like in a a chemical equation. Gamma particles are electromagnetic waves (photons) hence have no rest mass like other electromagnetic waves. You cannot use stoichiometrice ratio like in chemistry and electrons and gamma particles are different. Electrons exhibit wave-particle duality unlike gamma particles.