Physics: Post your doubts here!

[Suchal Riaz]

chocolate_girl
question number 7
the air resistance is zero. the only acceleration is of gravity. and on earth gravity is a constant which will be same for any points on that trajectory.
question numnber 20

 

[Suchal Riaz]

Is answer A ?

no it is C
according to the given information R3 gives 2 volt out of 5. which means R3/(R1+R2+R3) * 5
in C only this equation gives 2 volts as expected.
4/10 * 5 = 2V

 

[Suchal Riaz]

diff of pd across R1 is 2 then R2 is 1 nd R3 is 2 hence R1 nd R2 will hv same resistance

C is correct.

 

[chocolate_girl]

2) A and D must not be the answer, Its obvious.
the answer is C. because unit current is not like unit charge.
current is how many electrons in a second i.e. e/second, which has Amps as its unit.
Charge is Coulomb with a unit C. so both of them are NOT the same.
p.d.= work done/unit charge NOT work done/current SO Answer is not B

7) 20) Suchal Riaz ZaqZainab

31) Before we select an answer, let's review what each answer means.

A. The mathematical expression of this statement is F = E*q. Voltage (potential difference) is not a force, and the E here is an electric field not a difference in potential, so this answer cannot be correct.

B. Energy = V*q = d*E*q is the mathematical expression referred to here. Since I (current) = dq/dt, q = I*t (current is the derivative of charge with respect to time, thus total charge is current times total time passed). This means Energy = V*q (voltage times charge) = V*I*t (voltage times average current times time elapsed), which can be rearranged to say V = E/(I*t). This is not the ratio of energy to current, rather the ratio of energy to charge passed, so this answer cannot be correct.

C. Power = V*I. Thus V = P/I. This is a correct assessment of potential difference. Saying that potential difference in a wire is equal to the ratio of power to current is correct, since V = P/I, so this answer is acceptible.

D. P = V*I = V*dq/dt, which means V = P/(dq/dt). You can go one step further and integrate the top and bottom of this equation and say V = int(dE/dt)/int(dq/dt) = E/q. In neither case is the potential difference the ratio of power to charge moved, it is either the ratio of power to charge moved per second (current), or it is the ratio of the energy dissipated to the charge moved. So this answer is unacceptible.

Thus the answer is C.

thanks and in mcq 2 y is it obvious that A and D r incorrect?

 

[chocolate_girl]

chocolate_girl
question number 7
the air resistance is zero. the only acceleration is of gravity. and on earth gravity is a constant which will be same for any points on that trajectory.
question numnber 20
View attachment 39803
View attachment 39804

y did u take height for column q as x and not 2x?

 

[Thought blocker]

thanks and in mcq 2 y is it obvious that A and D r incorrect?

If A was true, then mass per cubic inch would not be density. If D was correct, then mile per hour would not be speed.

 

[talha-_-khan]

Is answer A ?

no The answer is c and this is how i got the answer

 

[Thought blocker]

no The answer is c and this is how i got the answer

Suchal Riaz Quoted me :
according to the given information R3 gives 2 volt out of 5. which means R3/(R1+R2+R3) * 5
in C only this equation gives 2 volts as expected.
4/10 * 5 = 2V

 

[talha-_-khan]

THE ANSWER SHOULD BE 1/3 V , BUT THE ANSWER IN BOOK IS 2/3 V

 

[Martee100]

Could someone help me with May/June 07 Paper 4 Q2 c

 

[Suchal Riaz]

y did u take height for column q as x and not 2x?

i am not taking the pressure on the bottom. you can't do that. i am taking pressure as where i pointed out in that picture. see it again.

 

[Suchal Riaz]

THE ANSWER SHOULD BE 1/3 V , BUT THE ANSWER IN BOOK IS 2/3 V

the answer is correct. its 2/3 V how did you do it?

 

[Suchal Riaz]

THE ANSWER SHOULD BE 1/3 V , BUT THE ANSWER IN BOOK IS 2/3 V

the potential on the first wire is 5/15 * 2 = 2/3 V
potential in the second wire is 10/15 * 2= 4/3 V
their difference is 2/3 V
which is potential difference.
i know why you are confused.
the place where the wire is joining is actually where there is a little dot. that is junction. where the wire pass straight through it is not a junction.
this might help

 

[chocolate_girl]

i am not taking the pressure on the bottom. you can't do that. i am taking pressure as where i pointed out in that picture. see it again.

U took 2x for height in Pp and x for height in Pq, i dont get y u dint take that x im so sorry for troubling so much but i dun ge it

 

[chocolate_girl]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w05_qp_1.pdf

Mcq 11
Y is the ans B wen both forces should be giving resultant?
Suchal Riaz

 

[hela]

% uncertainty
how to calculte it
http://freeexampapers.automaticpapers.com/as-a-level/physics-9702/9702_w13_qp_51.pdf
paper 51 Q 2 e) ii

 

[mahabaloch]

i need to sleep. i will answer in the noon today. if i forget please remind me.

Hey you didn't answer... Plz help me

 

[hela]

% uncertainty
how to calculte it
http://freeexampapers.automaticpapers.com/as-a-level/physics-9702/9702_w13_qp_51.pdf
paper 51 Q 2 e) ii

 

[talha-_-khan]

the potential on the first wire is 5/15 * 2 = 2/3 V
potential in the second wire is 10/15 * 2= 4/3 V
their difference is 2/3 V
which is potential difference.
i know why you are confused.
the place where the wire is joining is actually where there is a little dot. that is junction. where the wire pass straight through it is not a junction.
this might help

Now i got it thanks

 

[farhan141]

How is the potential of second wire 10/15 *2 i am confused shouldn't it be 5/15

Because of the resistors (4) being in parallel (2) and series (2)... The first wire has 2 resistors in parallel. I hope Im correct :3