# Physics: Post your doubts here!

#### hellodjfos;s'ff

And plz tell me how will the intensity be calculated from the amplitude. Amplitude² is proportional to intensity but how will the value be calculated as we don't know of any constant in this equation.
P.s should't the microphone be placed beside the speaker with a barrier in between? And to measure the amplitude of incident wave a cro should also be connected to speaker. Is it so?
This one may sound silly but that's okay Don't we need to give any electricity supply to the microphone?
Yes we would use the relation for intensity and amplitude(intensity is directly proportional to amplitude squared). You need not explain how to calculate k(intensity in terms of k should be fine).
Yes the microphone will be placed besides the speaker but in a side-view diagram, that is impossible to show hence I have shown them infront of each other.
You are measuring the amplitude of the wave that get reflected from the wall and foam, so you would connect CRO to microphone, not the speaker.
Yes we need to give a supply to the microphone but that's not really important to the question here - it would be a waste of space on the diagram and would make the diagram messy. You could mention it in the space below.

#### A*****

Yes we would use the relation for intensity and amplitude(intensity is directly proportional to amplitude squared). You need not explain how to calculate k(intensity in terms of k should be fine).
Yes the microphone will be placed besides the speaker but in a side-view diagram, that is impossible to show hence I have shown them infront of each other.
You are measuring the amplitude of the wave that get reflected from the wall and foam, so you would connect CRO to microphone, not the speaker.
Yes we need to give a supply to the microphone but that's not really important to the question here - it would be a waste of space on the diagram and would make the diagram messy. You could mention it in the space below.
Ok thank u so much! Just a little thing, we need the intensity of sound wave before reflection as well as mentioned in the formula so I think that needs to be measured as well

• hellodjfos;s'ff

#### Ebrahim12

Yes, that would be determined by removing the foam and measuring the intensity of reflected wave with wall only.
You are talking about I₀ here? it would be the incident wave, ie the wave produced by the speaker not the one reflected by the wall

• A*****

#### hellodjfos;s'ff

You are talking about I₀ here? it would be the incident wave, ie the wave produced by the speaker not the one reflected by the wall
Oh yeah alright. Didn't read the question properly. Yeah Io would be the intensity of wave with no reflection so in that case you would place the microphone really close to speaker and facing it and measure the intensity.

• A*****

#### A*****

What was the error in T?

#### hellodjfos;s'ff

What was the error in T?
It varied depending on the values of t for example one set of values were 9.0 and 9.8s. Here the period would be 9.4/20 but the uncertainty would be ( (9.8/20)-9/20)/2 - basically the max and min value method of finding uncertainty: max value-min value/2

• A*****

#### blymphocytes

It varied depending on the values of t for example one set of values were 9.0 and 9.8s. Here the period would be 9.4/20 but the uncertainty would be ( (9.8/20)-9/20)/2 - basically the max and min value method of finding uncertainty: max value-min value/2
What variant is this?

Did anyone do variant 1 (51)? The paper was really easy.

#### blymphocytes

Did anyone do variant 1 (51)? The paper was really easy.
Yes it was...

#### A*****

It varied depending on the values of t for example one set of values were 9.0 and 9.8s. Here the period would be 9.4/20 but the uncertainty would be ( (9.8/20)-9/20)/2 - basically the max and min value method of finding uncertainty: max value-min value/2
So if you do by this method, the mean time is 9.4±0.1s so isn't max value 9.41 and min 9.39? Error in T will then be 0.005
And if we apply the other rule that if a quantity is being multiplied or divided by a number, then the error in the calculated quantity is error in previous quantity times the number. In this case it would have been 0.1/20 = 0.005 for all values of T

#### hellodjfos;s'ff

So if you do by this method, the mean time is 9.4±0.1s so isn't max value 9.41 and min 9.39? Error in T will then be 0.005
And if we apply the other rule that if a quantity is being multiplied or divided by a number, then the error in the calculated quantity is error in previous quantity times the number. In this case it would have been 0.1/20 = 0.005 for all values of T
What? Mean time would be 9.4s but with an uncertainty of 0.4s. Mean period would be 0.47 with an uncertainty of 0.02s.
And if we apply the other rule that if a quantity is being multiplied or divided by a number, then the error in the calculated quantity is error in previous quantity times the number. In this case it would have been 0.1/20 = 0.005 for all values of T
Oh we can't use the multiplied or divided rule in this because the calculations only involved one variable that had one uncertainty. So we had to use max-min values/2 - really the only method.

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#### Maiday Holsey

Hi guys. For those who took Paper 21 in AS Level Physics today, which formula should have been used to calculate the charge of the oil drop in the electric field question?

#### Hamza Umair

How do I study for physics practical

#### hellodjfos;s'ff

How do I study for physics practical
Look over mark schemes for question 2's last part and also just read the ECR for P3 - example candidate responses.

#### FarGang

Any idea regarding the grade boundary for A? I did AS and A level separately?

#### FarGang

Any idea regarding the grade boundary for A? I did AS and A level separately?

#### Maiday Holsey

Hi. Has anyone done Paper 11 today? How hard did you find it?

#### Samatar011

It was pretty good, just a couple questions I found hard.
What did you think of it?

#### Maiday Holsey

It was pretty good, just a couple questions I found hard.
What did you think of it?
Same