phy P4 help

[princesszahra]

1 can some one explain question number 6 in june 2004.
2 in june 2005 question number 3 part b
the values of specific heat capacity has unit Jkg^-1K-1
but mark scheme solved this without changing the temperature into kelvin
so how do we know when to change and when not to?
3 in nov 2008 Q 8 , can someone explain why the answer is magnetic field for the last part?
4. june 2008 Q11 aii part 2
june 2008 Q6 part c
for some of these i know the answes but i need someone to explain
it will really kind if anyone can answer even one of these
thanx alot for ur time!

 

[Zohaib Sherazi]

1- First of all we need to know the definition of Ideal gas: " An Ideal gas is a hypothetical gas with molecules of negligible size that exert no intermolecular forces"

Next, you've got too see the definition of internal energy: "Internal energy is defined as the energy associated with the random, disordered motion of molecules."

Am quite sure you must have understood the solution to the first row by these definitions. Still, i'll state it here: There's no change in Internal Energy as the molecules do not anyway apply an intermolecular force. Compression causes a loss of heat. Work is done as a force is applied to compress it. Therefore, 0, -, +

Heating supplies the energy to molecules. Hence, an increase in internal energy. Next, obviously the thermal energy will increase as heat is being supplied. And supplying thermal energy alone does no work. Therefore, +, +, 0

This one is pretty straightforward. Ice melts...heat is supplied...thermal energy increases...supplying heat alone does no work. (why heat? the heat is used to change the state of ice). So, +,+, 0.

2-By definition specific heat capacity: "is the amount of energy in joules required to increase the temperature of 1 kg of a substance by 1 K (equivalent to 1 °C)"

Got it? I hope.

3-By definition, frequency modulation will vary the frequency of the carrier signal.

The maximum amplitude of the signal of interest is Vsignal, and the frequency conversion of signal voltage amplitude is vconf (V convert to f...this is the 20 kHz/Volt value).

Thus, the frequency variation amplitude will be :
f_amp = Vsignal*vconf

And with frequency modulation, our carrier wave will vary in frequency from:
fmin = fcarrier - f_amp
fmax = fcarrier + f_amp

Thus:
fmin = fcarrier - Vsignal*vconf
fmax = fcarrier + Vsignal*vconf

Data:
Vsignal:=1.5 Volts; vconf:=20 kHz/Volt; fcarrier:=500 kHz;

Results:
fmin = 470 kHz
fmax = 530 kHz See below for an idea



Conclusion: our output wave will vary in frequency from 470 kHz to 530 kHz (Ok, am not a telecom engineer but that detail was to provide some evidence behind that

4-Just keep in mind that magnetic field is a phenomena that is a result of charges moving with respect to a location of interest.

This is a simple application of Magnitude of F = BIL sinθ where θ is the angle made between conductor and B.
(OR F = BIL where B and L are 90° to one another.) And that m stands for 10^-3 i.e. Milli.

 

[princesszahra]

sorry ppl but i got more doubts
1 june 2006 Q6 part a
2 june 2006 Q7 part a
3 june 2007 Q2 part C i and ii
4 june 2007 Q7 part b

@ zohaib
thanx bhaiya for helping so much!
really really kind of u for taking out some time and helping me!
thanx again!

 

[princesszahra]

some more doubts comming in
1 june 2007 Q3 part a and b
2 nov 2002 Q2 part b
3 nov 2003 Q2 part b ii
what is the significance of the -ve sign

 

[Zohaib Sherazi]

1- When the current is in the same direction the wires attract each other (by the right hand rule).

The force is towards the left due to attraction. The direction of the magnetic field can be identified by the right hand rule.

2-A particle is any object that will move in a straight line. A beam is a bundle of rays, all of them will hit the screen in straight line. Hence, they will be 'uniformly' distributed.

3- 160/1000 = 0.16 kg water in the ice 365-160 =205 205/1000 =0.205kg

Energy used to melt ice = Loss of thermal energy.

thermal energy loss => 0.16 × 4.2 x 100= 67.2 kJ

67.2 = 0.205 X L

Therefore, L = 328 KJ/Kg.

4- The only major factor here is to see that damping decreases as resistance increases.

....Replied some random ones. Will do the rest later today.

 

[princesszahra]

thanx
how to chnage a number into binary form?

 

[Zohaib Sherazi]

Use this http://www.ieeeghn.org/wiki/index.php/B ... inary_Math

 

[princesszahra]

they dont explainn abt binary in the above link
can u see where exactly it is and give the link again

 

[Zohaib Sherazi]

This is more precise i think, see if it helps. If it doesn't then lemme know, i'll explain myself.

http://wiki.answers.com/Q/How_to_conver ... inary_form

 

[princesszahra]

i need the thing changing a number only into 4 bits not more than that

 

[Zohaib Sherazi]

For the 4 bit binary value:

Place: 0 0 0 0

Value: 8 4 2 1

Any number up to 15 will fit, and there are 16 combinations (including 0).
Start at the left and subtract each quantity if you can. If you can, it's a 1.

Example: 11
You can subtract 8 from 11, so the first digit is a 1.
3 remains, you cannot subtract 4 from 3, so #2 is a 0.
you can subtract 2 from 3, so the next digit is a 1.
You can subtract 1 from 1, so the last digit is a 1.

Therefore, 11 in binary is: 1011

 

[princesszahra]

thanx
nov 2003 Q4 ii 2
nov 06 Q6 a ii
nov 06 Q8 c
nov 2007 Q1 part b
nov 07 Q10 c
most imp june 07 Q3 part b how to find the area ?
use integration?

 

[princesszahra]

nov 03 Q2 b ii
significance of -ve sign????????????????????

 

[princesszahra]

june 2008 Q2 c
nov 2007 Q10 part c

 

[mariam]

need help in jun 08/ question 12 part (b) :?

 

[Vnza]

Binary Conversion:

Write:

8 4 2 1

These are the powers 3,2,1 and 0 respectively of 2. Now if you want to covert 5 into binary:

8 4 2 1
0 1 0 1

Write 1 under 4 and 1 under 1 as 4 + 1 + 5. Write 0 under the column of 8 and 2. Now 5 in binary is 0101. The first bit (0) is the MSB while the last bit (1) is the LSB.

I am a computing student. Anymore questions? Fire away!

 

[Vnza]

Does anyone have 01-99 marking schemes for phy p1 and p2?

 

[princesszahra]

i think u dont need to go through such old papers!
syllabus has changed so its better u do latest papers!

 

[PlanetMaster]

In old papers, AS & A2 was combined.
Attempting to solve those paper's will worsen your concepts.:!:

 

[princesszahra]

thats very true u can solve old papers for maths and the practicals
but not theory