Physics: Post your doubts here!

[ZaqZainab]

Please help Usama321 & ZaqZainab and others
The electric power consumed by a device may be calculated by using either of the two expressions P=I2R or P=V2/R.
The first expression indicates that it is directly proportional to R whereas the second expression indicates inverse proportionality.
How can the seemingly different dependence of P or R in these expressions can be explained?

It depends on whether you have constant voltage or constant current if you have a constant voltage, increasing the resistance decreases the current flowing in the system by Ohm's law and hence decreases the power consumption P = IV - decrease I, decrease V.However, if you have a constant current source, increasing the resistance increases the voltage dropped across the resistor and hence increases the power consumption.
So in one case increasing R decreases power (P=V^2/R) and in the other increasing R increases power (P=I^2R)

 

[NinjaInPyjamas]

Q: A number of identical springs, each having the same spring constant, are joined in four arrangements. A different load is applied to each arrangement.
Which arrangement has the largest extension?

A: 2 springs in series; 2N
B: 3 springs in series; 1N
C: 2 springs parallel; 6N
D: 3 springs parallel; 8N

 

[Sam Ivashkov]

it cnt show the reading of 6A for two resistors...
here we r assumng 6A as I... for option A when S1 is closed then the current won't pass through the second resistor becuz current always chooses low resistance path... so for A our answer will be 12/2=6A i.e. I
n for C it is 3A i.e. I/2

got it! thank you so much

 

[mehria]

got it! thank you so much

my pleasure

 

[Snow Angel]

question 1 b) from oct nov 2007 paper 2 as level physics: why do they halve the percentage uncertainty from 3.8 to 1.9?

question 2 d) ii) from the same paper: why do they add the resistive force and the accelerating force instead of finding the difference?

please reply as soon as possible. thanks in advance

 

[mehria]

question 1 b) from oct nov 2007 paper 2 as level physics: why do they halve the percentage uncertainty from 3.8 to 1.9?

question 2 d) ii) from the same paper: why do they add the resistive force and the accelerating force instead of finding the difference?

please reply as soon as possible. thanks in advance

for Q1 (b) :- it is R(squared) n we r supposed to find the uncertainty in R not in R(squared) that's y we divide it by 2

 

[mehria]

I like them .have you made them for other topics if so please post it would be really helpful
Thanks in advance

i would luv to post them but they r nt neat at all.... my frnds has written stuff on them which i dnt want anyone to read
still if i get tym then i'll take the snapshots of the neat ones n post them

 

[ZaqZainab]

i would luv to post them but they r nt neat at all.... my frnds has written stuff on them which i dnt want anyone to read
still if i get tym then i'll take the snapshots of the neat ones n post them

please do

 

[hope4thebest]

How are currents in primary & secondary coils of transformer 180 out of phase? Anybody?

 

[Thought blocker]

How are currents in primary & secondary coils of transformer 180 out of phase? Anybody?

http://www.answerl.com/q/how-are-primary-and-secondary-coils-180-out-of-phase-in-a-transformer

 

[Snow Angel]

for Q1 (b) :- it is R(squared) n we r supposed to find the uncertainty in R not in R(squared) that's y we divide it by 2

thanks wat abt question 2 d ii)?

 

[Snow Angel]

what is meant by lamp is shorted ?

 

[Snow Angel]

can someone please explain question 7 a) and b) from may june 2006 paper 2 as level physics. thanks in advance.

 

[ashcull14]

help plzzz

 

[ashcull14]

what is meant by lamp is shorted ?

maybe...related to short circuit..if lamp goes out

 

[Thought blocker]

maybe...related to short circuit..if lamp goes out

Its a standing wave, so the 33cm is the distance between two nodes. The wavelength thus becomes .66m. F = 330/. = 500. T = 1/500 = 0.002s = 2ms. B is the right answer
usama321 thank you

 

[ashcull14]

explain fully plx...i know its ez bt i guess im doin smethin wrong getting a as the ans though its b

 

[ashcull14]

Its a standing wave, so the 33cm is the distance between two nodes. The wavelength thus becomes .66m. F = 330/. = 500. T = 1/500 = 0.002s = 2ms. B is the right answer
usama321 thank you

igot the same calculated results bt how did u conclude tht its b ..cn u explain fully plx?

 

[Thought blocker]

igot the same calculated results bt how did u conclude tht its b ..cn u explain fully plx?

usama321 help her.

 

[NinjaInPyjamas]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w12_qp_13.pdf

q24

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w12_qp_11.pdf

q23