Physics: Post your doubts here!

[Saad the Paki]

Please someone explain this I have no idea how to do this.

 

[sj0007]

A standing wave is produced when two waves are moving in opposite direction to each other which have the same frequency, wavelength and speed. So when the two loudspeaker are positioned in opposite direction a standing wave is produced

Ummm okay........ But what I don't get is why isn't it B or C then?
Since B has two speakers in the opposite directions and C has a reflection (which in the question is set up).........

 

[sj0007]

View attachment 59612
Please someone explain this I have no idea how to do this.

I don't think I have the proper explanation behind it but how I did it was that x+y has to be 50 and x has to be the smaller one......... This leaves us with only option B.......... And I think the answer is B ?

 

[Saad the Paki]

I don't think I have the proper explanation behind it but how I did it was that x+y has to be 50 and x has to be the smaller one......... This leaves us with only option B.......... And I think the answer is B ?

So is C. X+Y is 50. And don't say that X is smaller in the diagram cuz it's not to scale and yes the ans is B

 

[sj0007]

So is C. X+Y is 50. And don't say that X is smaller in the diagram cuz it's not to scale and yes the ans is B

Oh I never noticed the Not to scale thing..........
Like I said, I don't think I have a proper explanation but I guess it has something to do with the excess pressure and stuff

 

[Maayee]

can someone pls help me with this..
http://papers.gceguide.com/A Levels/Physics (9702)/9702_w15_qp_43.pdf
Q10 a an b and also 12 c

 

[Marinaa1998]

http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_s09_qp_4.pdf
I need someone's help with Q10 (b) please!

 

[Maayee]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s09_qp_4.pdf
I need someone's help with Q10 (b) please!

this is a non inverting amplifier so the formula for the gain is G=1+R1/R2
so 25=1+120/R
24R=120
R=5

 

[Marinaa1998]

this is a non inverting amplifier so the formula for the gain is G=1+R1/R2
so 25=1+120/R
24R=120
R=5

Thanks a lot for your help! Can you please help me with (c)(i) as well?

 

[Maayee]

Thanks a lot for your help! Can you please help me with (c)(i) as well?

sure
ok so u need to find Vout so the formula is Gain=Vout/Vin
u already know ur gain 25 and Vin as -0.08 so Vout is 25x0.08=2V

 

[Marinaa1998]

sure
ok so u need to find Vout so the formula is Gain=Vout/Vin
u already know ur gain 25 and Vin as -0.08 so Vout is 25x0.08=2V

thank u so much

 

[Iris Dylan Lane]

What happens to the spring constant if the cross-sectional area is doubled?

 

[Muhammad Amer]

Can anyone help me with this?

"A power supply of e.m.f. E and internal resistance R is connected to a 10 kΩ resistor. The current drawn from the power supply is 0.91 mA. A voltmeter of internal resistance 10 kΩ is connected in parallel with the 10 kΩ resistor, and reads 8.3 V. Calculate the e.m.f. and the internal resistance of the power supply."

This question should be answered using Kirchhoff's laws.

 

[The Sarcastic Retard]

What happens to the spring constant if the cross-sectional area is doubled?

Doubled.

 

[muhammadali233]

Physicist http://physics-ref.blogspot.com/2015/05/physics-9702-doubts-help-page-158.html
Q-784 is done wrong
L = 1/2*gT² , if T--> T/2 => 1/2*g*(T/2)² = 1/2*g*T²/4 = L*1/4

Answer: 0.25 L (B)

 

[Maayee]

can someone pls help me with this..
http://papers.gceguide.com/A Levels/Physics (9702)/9702_w15_qp_43.pdf
Q10 a an b and also 12 c

 

[princess Anu]

Book says :

1.Back Emf seems to imply opposition, something not wanted, yet in a motor it is the induced emf that is responsible for the mechanical work output of the motor.
2.The workdone against the induced emf in a motor is the useful work output of the motor. Workdone against the resistance of the wires is wasted as thermal energy

Can someone explain please?
How is back emf responsible for the ouput of a motor? :S

 

[AnonymousX9]

Guys pls help, M/J 2009 P22 Questions 3(b), 4(b) and 7(a).. ??? Please

 

[Eugene99]

Which book should I chose for Physics?

 

[Muhammad Amer]

Which book should I chose for Physics?

Probably Cambridge International AS and A Level Physics Coursebook with CD-ROM