Physics: Post your doubts here!

[biscuitbiscuit]

Someone please explain Q7 b (i) and (ii), link:

http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_w08_qp_2.pdf

 

[♫Prince Shah♫]

Someone please explain Q7 b (i) and (ii), link:

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w08_qp_2.pdf

bi)As temperature increases, Resistance of a thermistor decreases ...so, talking abut Potential diff of 2kohm voltage reading increases so u can also say that pd across 5kohm.. thermistor resistance decreases..!!!
bii) i am not sure

 

[boredome]

Can u

(a) 1. Alternating current will produce an magnetic field(Flux) in the core so due to this there wil be change in flux in secondary coil and then emf will be induced in the secondary coil.

2. the power is contant ..ie the input power given should be equal to the output power so if V is increased the I will be decreased to reduce the power losses.

(b)1.current I is directly proportional to Flux so the graph will have same shape as of the above graph shown in the question .
2. the shape of this graph will be of cosine graph ... when flux is zero emf is max and when flux max then the emf is 0.

Can u please write the equation or explain how Current is directly proportional to magnetic flux?

 

[!!..Purple Ghost..!!]

Can u


Can u please write the equation or explain how Current is directly proportional to magnetic flux?

The amount of current in a coil directly relates to magnetic field strength
Moving charges create magnetic fields. Each electron moving in a conductor creates its own magnetic field. As electrons move through the coil of wire, the magnetic field of one electron adds to the field of any others moving in the same direction. The faster a charge moves, the stronger the magnetic field it creates. For this reason alone, a higher current implies an electron is moving faster, and as a result, it would create a stronger magnetic field.

 

[BreakingBad]

A model is made of the crane, its load and the cable supporting the load.
The material used for each part of the model is the same as that in the full-size crane, cable and
load. The model is one tenth full-size in all linear dimensions.
What is the ratio
stress in the cable on the model crane
stress in the cable on the full s ize crane
- ?
A 100 B 101 C 102 D 103

Stress is force per unit area. The area is a hundred times smaller so A probably. Besides, options B,C and D are absurd. It would make more sense if those numbers were more like 1000 times, 10 times etc.

Someone please explain Q7 b (i) and (ii), link:

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w08_qp_2.pdf

i) Already been answered.
ii)
P.d. across the thermistor and the 5000 ohms resistor combined is 6-3.6 = 2.4V
The current in the circuit is V/R = 3.6/2000 = 0.0018A

Therefore, combined resistance for the thermistor and the 5000 ohms resistor is V/I = 2.4/0.0018 = 1333.333 ohms

1/RT = 1/Rt + 1/Rr
1/1333.333 = 1/Rt + 1/5000
Rt = 1820 ohms
Sorry but I haven't been looking at most of the convos lately.

 

[!!..Purple Ghost..!!]

h3lp me in electronics part.. i cant understand it at all As level..

 

[Cute Angella]

can someone pls help me out with this...
M/J/06 P4 q2 b(ii)

and O/N/07 P4 q3 b(ii) 2
how can we use the graph in this question...i got the answer by using the formula KE=1/2mw2 A2...but i dont know how to use the graph..???

 

[Cute Angella]

O/N 06 P4 q7 b (phy A2)
what i know is that frequency of light hv no effect on the rate of emission of electrons.... rate only depends on the intensity of light.... n here light intensity is constant.... so how does the rate decreases..???? n how the photons r fewer per second at higher frequency ???????

 

[Cute Angella]

M/J/09 P4 q9 b
can someone pls explain why the source must decay by 8% ???

 

[mahabaloch]

anyone can help me with nov 07 q5 part c plz

 

[Cute Angella]

anyone can help me with nov 07 q5 part c plz

first find the initial energy stored in the capacitor using the initial voltage...
E=1/2 CV^2
E=1/2 x 220 x 10^-6 x 15^2
E=0.02475 J
since half of this energy is lost so only half is left behind
so divide this energy by 2 to get half of it
E=0.012375 J
now with this left over energy find the voltage using the same above formula
E=1/2 CV^2
0.012375=1/2 x 220 10^-6 x V^2
V=10.6 V ...
hope u get it ..

 

[shaheerrn]

Stress is force per unit area. The area is a hundred times smaller so A probably. Besides, options B,C and D are absurd. It would make more sense if those numbers were more like 1000 times, 10 times etc.


i) Already been answered.
ii)
P.d. across the thermistor and the 5000 ohms resistor combined is 6-3.6 = 2.4V
The current in the circuit is V/R = 3.6/2000 = 0.0018A

Therefore, combined resistance for the thermistor and the 5000 ohms resistor is V/I = 2.4/0.0018 = 1333.333 ohms

1/RT = 1/Rt + 1/Rr
1/1333.333 = 1/Rt + 1/5000
Rt = 1820 ohms
Sorry but I haven't been looking at most of the convos lately.[/quote

no these are powers A.10^0 B.10^1 C 10^2 D. 10^3
and the answer is B

 

[shaheerrn]

explain how the collisions in an ideal gas are elastic

 

[shaheerrn]

i solved it myself
thanks anyways

 

[BreakingBad]

explain how the collisions in an ideal gas are elastic

You solved this?

 

[shaheerrn]

You solved this?

no the other one
in which we had to find the ratio

 

[Salman917]

how will we understand wen to use mv^2/r=GMm/r^2 N wen 2 use 0.5mv^2/r=GMm/r^2???????????????????

 

[Cute Angella]

how will we understand wen to use mv^2/r=GMm/r^2 N wen 2 use 0.5mv^2/r=GMm/r^2???????????????????

i don't think we ever use the second equation..!!!!
we always use the first one where centripetal force is provided by the gravitational force.....

 

[BreakingBad]

how will we understand wen to use mv^2/r=GMm/r^2 N wen 2 use 0.5mv^2/r=GMm/r^2???????????????????

When you are relating forces, you use mv^2/r because centripetal F = mv^2/r and Gravitational F = GMm/r^2
When you are relating energies, you use 1/2mv^2 because (K)E = 1/2mv^2 and GPE = -GMm/r (You don't equate the 2 though, usually)

 

[Cute Angella]

can someone pls help me out with a few questions of phy A2.....
1. M/J/06 P4 q2 b(ii)
link =http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_s06_qp_4.pdf

2. O/N/07 P4 q3 b(ii) 2
how can we use the graph in this question...i got the answer by using the formula KE=1/2mw2 A2...but i dont know how to use the graph..???
link =http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_w07_qp_4.pdf

3. O/N 06 P4 q7 b
what i know is that frequency of light hv no effect on the rate of emission of electrons.... rate only depends on the intensity of light.... n here light intensity is constant.... so how does the rate decreases..???? n how the photons r fewer per second at higher frequency ???????
link =http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_w06_qp_4.pdf

4. M/J/09 P4 q9 b
can someone pls explain why the source must decay by 8% ???
link =http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_s09_qp_4.pdf

pls someone do help..!!!