Physics: Post your doubts here!

[TheJDOG]

who knows how to hack an email ?? urgently needed and for sure can hack the email not i think or ill try... for AS

Why would you even want to hack an email?

 

[Suchal Riaz]

m/j /2005/paper4/q7 last part please explain me properly

initially mass was 1.4x10-6 g. when one nucleus of Mg decays it produces one nucleus of Fe. that means mass of Mg that has decayed = mass of Fe produced. that means total mass will always be equal to 1.4x10-6 g
Mfe/Mmg=9 but mfe+mmg=1.4x10-6
substitution of one equation into another gives 9Mmg+Mmg=1.4x10-6 that gives 10Mmg=1.4x10-6 or Mmg=1.4x10-6 / 10 which means 1/10 th of the initial value. got it?
in one half life mass is 1/2 in two half lives mass is 1/4 so if there are n half lives mass is (1/2)^n
1/2^n = 1/10
find n using log properties as n=3.32
so total time = half life * n = 3.32*2.6 = 8.63 hours

 

[NIM]

Hey I attached them for you.
For Q6 a) use right hand rule, thumb along current direction and other fingers along magnetic flux direction.
b) i) use Flemings left hand rule, thumb is direction of force, first finger direction of flux and second finger direction of current, then, do this to both magnetic field of earth and magnetic field due to wire, you'll see forces at Point P will be equal and opposite.
ii) just use given equation and substitute


Yes, my sketches are very bad , I'm sorry :/
Also, I just checked the ms, why am I not allowed to say increase R for more smoothing, only larger capacitor, anyone could explain this to me please? This is Q7 c)ii)1)
Also, tell me if I have any mistake and thanks

Thankyou so much for help but can u plz show me the exact position of P in Q#6 ii
And question 7 b, question # 10 also

 

[Zash Riyash]

The answer is: D

 

[Zash Riyash]

R+[1/(1/R+1/R)]+[1/(1/R+1/R+1/R)]=66000

Then:
R+[R/2]+[R/3]=66000

Solve this and you get the answer.

 

[nehaoscar]

http://www.cie.org.uk/images/157397-november-2012-question-paper-22.pdf

Question 5 part B please explain!
I know that p.d
AC = 4.8V
BC = 7.2V
AD = 8V
BD = 4V

Now it's asking pd between CD so wouldn't CD be either CB + BD
or CA + AD

But the answer is 3.2V which means they are subtracting... why??

 

[Zash Riyash]

http://www.cie.org.uk/images/157397-november-2012-question-paper-22.pdf

Question 5 part B please explain!
I know that p.d
AC = 4.8V
BC = 7.2V
AD = 8V
BD = 4V

Now it's asking pd between CD so wouldn't CD be either CB + BD
or CA + AD

But the answer is 3.2V which means they are subtracting... why??

They are subtracting it because they have said calculate the potential difference, which generally means that the difference in voltage. Hence, we must subtract. I hope you understood!

 

[yasoob_shah]

http://qualifications.pearson.com/c...2013/Exam materials/6PH07_01_que_20130509.pdf
question 2 4 and 5...help needed ASAP

 

[Zash Riyash]

Question 2 is D

 

[yasoob_shah]

Question 2 is D

dada why and how?

 

[Zash Riyash]

dada why and how?

Huh? We first convert mm to metres and then chose the median value which is .71 and addition of .1 would give .72 and subtraction of .1 from .7 would in turn give .69

 

[yasoob_shah]

Huh? We first convert mm to metres and then chose the median value which is .71 and addition of .1 would give .72 and subtraction of .1 from .7 would in turn give .69

ok tysm....got it...thnx one again

 

[nehaoscar]

They are subtracting it because they have said calculate the potential difference, which generally means that the difference in voltage. Hence, we must subtract. I hope you understood!

But then say they would've asked you the pd between A and B, then you would add the pd's right?
How do you know when to subtract and when to add?

And also say if they would've used 'voltage' instead of 'potential difference' then would you add?

 

[nehaoscar]

http://qualifications.pearson.com/content/dam/pdf/A Level/Physics/2013/Exam materials/6PH07_01_que_20130509.pdf
question 2 4 and 5...help needed ASAP

Question 4 is B
Frequency = 1/time period
Time period for one complete oscillation = 4 boxes = 4ms = (4 x 10^-3) seconds.
SO
Frequency = 1/(4 x 10^-3)
which = 250 Hz

 

[yasoob_shah]

Question 4 is B
Frequency = 1/time period
Time period for one complete oscillation = 4 boxes = 4ms = (4 x 10^-3) seconds.
SO
Frequency = 1/(4 x 10^-3)
which = 250 Hz

ohkayy thnxx alot

 

[Zash Riyash]

I just don't get it... Why would you ever add unless they ask the sum of the p.d, also if they had used the term voltage, then they would've certainly used the word, 'difference'.

 

[amal sharkawi]

Why the answer is B
Can anyone answer plz

 

[nehaoscar]

I just don't get it... Why would you ever add unless they ask the sum of the p.d, also if they had used the term voltage, then they would've certainly used the word, 'difference'.

So whenever they mention just pd, I subtract
and when they mention sum of pd, I add right?

So if in that question they said sum of pd accross CD then I would add the pd's right?

 

[Zash Riyash]

So whenever they mention just pd, I subtract
and when they mention sum of pd, I add right?

So if in that question they said sum of pd accross CD then I would add the pd's right?

Yup, but still google it, you might get a better idea.

 

[Lyfroker]

http://freeexampapers.com/A-Level/Physics/CIE/2002-Jun/9702_s02_qp_2.pdf

Q#1(b) & (d)