Physics: Post your doubts here!

[aalmuhannadi]

I've attached the questions:
The question is c)ii, the mark scheme says that the wave is reflected off of other surfaces, which I understand, but it also says that the path difference decreases and that the amplitude decreases which I don't get. What do they mean by a decreasing path difference and amplitude and how does it relate to minima? Can it be explained by relating it to the scenario in the diagram (ie difference when the mic close to the speaker and as it moves away) and the minima-maxima graph?

 

[snowbrood]

View attachment 21350View attachment 21351
I've attached the questions:
The question is c)ii, the mark scheme says that the wave is reflected off of other surfaces, which I understand, but it also says that the path difference decreases and that the amplitude decreases which I don't get. What do they mean by a decreasing path difference and amplitude and how does it relate to minima? Can it be explained by relating it to the scenario in the diagram (ie difference when the mic close to the speaker and as it moves away) and the minima-maxima graph?

minima is formed by complete destructive interference and for that to occur it must be in phase and the amplitudes should such that it cancels each other hope i could help

 

[aalmuhannadi]

minima is formed by complete destructive interference and for that to occur it must be in phase and the amplitudes should such that it cancels each other hope i could help

I thought that in phase waves cause constructive interference? and I understand that but what does the amplitude and path difference have to do with it?

 

[aalmuhannadi]

minima is formed by complete destructive interference and for that to occur it must be in phase and the amplitudes should such that it cancels each other hope i could help

Plus, how could te amplitudes at the minima even decrease because I thought that it must always be 0?!

 

[snowbrood]

I thought that in phase waves cause constructive interference? and I understand that but what does the amplitude and path difference have to do with it?

sorry about the phase stuff i wanted to write there is a path difference which means they are out of phase and thus cant cancel each other completely i.e (destructive interference) and zero minima here means no sound is this possible??? when u are actually moving loud speaker towards microphone

 

[snowbrood]

Plus, how could te amplitudes at the minima even decrease because I thought that it must always be 0?!

this minima is not the point where destructive interference takes place minima is also referred as the lowest point of a wave

 

[L-Girl]

guys, does anyone know how the marks are calculated for AS levels to get a mark out of 130?

 

[S.Mashaal.N]

please helpp!! :/View attachment 20937

here u go

 

[S.Mashaal.N]

could someone please tell me if its okay to break both the x-axis and the y-axis for the graphs in P3 of physics? Or are we supposed to break the x-axis?
a quick reply would be highly appreciated! thanks.

p.s. kindly reply

 

[Khunkar]

help needed........ 9702/s10/51 question no. 2.b)

 

[Ali_00921]

A thermometer can be read to an accuracy of ± 0.5 °C. This thermometer is used to measure a
temperature rise from 40 °C to 100 °C.
What is the percentage uncertainty in the measurement of the temperature rise?
A 0.5 % B 0.8 % C 1.3 % D 1.7 %............. THANKS IN ADVANCE

 

[Dug]

A thermometer can be read to an accuracy of ± 0.5 °C. This thermometer is used to measure a
temperature rise from 40 °C to 100 °C.
What is the percentage uncertainty in the measurement of the temperature rise?
A 0.5 % B 0.8 % C 1.3 % D 1.7 %............. THANKS IN ADVANCE

Percentage Uncertainty = (0.5 + 0.5)/60 x 100 = 1.6666 = 1.7 (2s.f)

 

[mamoon123]

How do we solve questions 14, 19 and 20 in this paper:
http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_s09_qp_1.pdf

 

[A*(a*)]

Percentage Uncertainty = (0.5 + 0.5)/60 x 100 = 1.6666 = 1.7 (2s.f)

Can you please tell me the uncertainities of all instruments to be used in phy and chem labs? I have been searching for them and with no luck. Like stopwatch having typical uncertainity of 0.2 due to human error .

 

[redrecession]

Can you please tell me the uncertainities of all instruments to be used in phy and chem labs? I have been searching for them and with no luck. Like stopwatch having typical uncertainity of 0.2 due to human error .

uncertainities of all instruments in phy are taken as their least counts eg. 0.1 mm in vernier caliper
as for in chem n bio uncertainities are taken to b 'half' of least count

 

[Ali_00921]

Percentage Uncertainty = (0.5 + 0.5)/60 x 100 = 1.6666 = 1.7 (2s.f)

But why (0.5+0.5)

 

[A*(a*)]

uncertainities of all instruments in phy are taken as their least counts eg. 0.1 mm in vernier caliper
as for in chem n bio uncertainities are taken to b 'half' of least count

and the least counts of the instruments are? sorry if it takes your time but I am in desperate need for them

 

[Dug]

But why (0.5+0.5)

Whenever we add or subtract 2 quantities, their uncertainty is added.

Change in Temperature = Final Temp. - Initial Temp.
Total uncertainty = ΔFinalT + ΔInitialT

 

[attitudehed]

Hi can someone help me with question 26 Nov/10/v2?
http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w10_qp_12.pdf
A microwave transmitter emits waves towards a metal plate. The waves strike the plate and are
reflected back along their original path.

A microwave detector is moved along the line PT.
Points P, Q, R, S and T are the positions where minima of intensity are observed. These points
are found to be 15mm apart.
What is the frequency of the microwaves?
A 5.0GHz B 6.7GHz C 10GHz D 20GHz
The answer is C. Can someone please explain how to get it?

 

[snowbrood]

Hi can someone help me with question 26 Nov/10/v2?
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_12.pdf
A microwave transmitter emits waves towards a metal plate. The waves strike the plate and are
reflected back along their original path.

A microwave detector is moved along the line PT.
Points P, Q, R, S and T are the positions where minima of intensity are observed. These points
are found to be 15mm apart.
What is the frequency of the microwaves?
A 5.0GHz B 6.7GHz C 10GHz D 20GHz
The answer is C. Can someone please explain how to get it?

distance between one minima to the other is 0.5 wavelength
0.5 wavelength=15*10^-3
wavelength =0.03m
we speed of the light is 3*10^8
frequency= velocity/wavelength
3*10^8/0.03 = we get 1*10^10
1*10^3 is kil0
1*10^6 is mega
1*10^9 is gega
so it is 10GHZ