Physics: Post your doubts here!

[hm12]

Can anyone explain me Q no. 38
Question: O/N 2011 Paper 12
Ans is A according to marking scheme.[/quote

combined resistance of voltmeter + 200kilo ohm resistor =100 kilo ohm total resistance = 400+100=500 kilo ohm total current across the whole circuit =60/500000=1.2 multiply by 10^-4 so now reading across the voltmeter = 1.2 into 10^-4 multiply by 100000=12V so the answer is A

 

[unique840]

Hey can anyone help me with this question? It's from O/N 11 52.. It says I should be varying the frequency of current in one coil to see
how the emf induced in the other coil varies. Now, a solution I suggested was to use a DC supply, and a switch attached to it. For a constant
time period say 10 seconds, I turned the switch on and off say 5 times for the first experiment. The frequency can thus be calculated by 5/10.
The same procedure is repeated with however greater number of times the switch is turned off and on for the same time period.
However, this particular solution was not suggested in the markscheme. Can anyone tell me if I will still be considered correct?View attachment 7088

i dun knw the ans to this ques but the emf is only induced when there is a change in magnetic flux. and that happens only when the current is alternating. not in dc

 

[abcde]

Q. Describe an experiment to determine the acceleration of free fall using a falling body.

 

[Rabib_69]

i dun knw the ans to this ques but the emf is only induced when there is a change in magnetic flux. and that happens only when the current is alternating. not in dc

yes, but u can also use a DC circuit to give altrenating current if u turn the switch on and off constantly.. and that's how i had explained it..

 

[Rabib_69]

D=-4cos 120=2 cm so the piston will be 2cm above AB and moving upwards as it is +2cm

So u just put the angle in that equation.. Can u explain the logic behind this.. Moreover, the second question says the phase difference is 240 degrees..
but d= -4cos240 = +2 which means this should also be in the +ve dir, whereas it is negative..

 

[namename]

How do you effectively find the area under the curves? I knw counting full squares and half-squres... but I always don't get the answer within the range (not problem of reading axis, units)

 

[histephenson007]

How do you effectively find the area under the curves? I knw counting full squares and half-squres... but I always don't get the answer within the range (not problem of reading axis, units)View attachment 7123

I guess counting squares is the best option available. If not that, you may try using Calculus, but you will need the f(x) of the curve to do that. I kinda suck at counting squares too - -

 

[elbeyon]

combined resistance of voltmeter + 200kilo ohm resistor =100 kilo ohm total resistance = 400+100=500 kilo ohm total current across the whole circuit =60/500000=1.2 multiply by 10^-4 so now reading across the voltmeter = 1.2 into 10^-4 multiply by 100000=12V so the answer is A

Thank you for solving but I din't get it properly. Aren't we supposed to use the equation:
Vout=(R2/R1+R2)*Vin

Can you please clearly mention the formula that you used and moreover where did that 100 kilo ohm came from ?

 

[elbeyon]

Q. Describe an experiment to determine the acceleration of free fall using a falling body.

Check this out:
http://mypages.iit.edu/~smart/martcar/lesson2/free-fall-experiment.html

It might seem quite boring but this really helps.

 

[Aahliya]

N=N knot e ^-lemda t
where Nknot = original number of undecayed nuclides at time t=0 so here N knot= 10 because original number was 10 out of which 9 decayed into iron and one was left
N=number of undecayed nuclides after time t so here N=1 as one manganese was left out of the 10 so 1=10e^-lemda t
lemda=0.693/2.6=0.2665 so overall t=ln10/0.2665=0.864hours

Thanks for replying.. but can u plss tell me how did u find the original no. of undecayed nulei and how can u say 9 decayedinto Iron and 1 was left as manganese ?? if u dun mind then can u plss explain me in detail..

 

[namename]

emf is the negative gradient of the given graph

thank you! so negative gradient of B graph is induced E (similar to electric field strength being negative potential gradient huh?) how about the one i posted earlier than that?? (in the same page (75th)

 

[hm12]

So u just put the angle in that equation.. Can u explain the logic behind this.. Moreover, the second question says the phase difference is 240 degrees..
but d= -4cos240 = +2 which means this should also be in the +ve dir, whereas it is negative..

the equation is d=-4cos220t where 220t is equal to omega multiply by t and u know teeta is equal to omega multiply by t so here theeta value is 120 so u simply put it in the place of omega multiply by t in the equation and in the second question d= 2 cm so the piston will be 2 cm above AB but in this case it has travelled all the way to CD and back towards AB

 

[hm12]

Thank you for solving but I din't get it properly. Aren't we supposed to use the equation:
Vout=(R2/R1+R2)*Vin

Can you please clearly mention the formula that you used and moreover where did that 100 kilo ohm came from ?

voltmeter and resistor is in parallel so resistance would be 1/R= 1/200 + 1/200=1/100 so R= 100 kilo ohm and i just simply used the formula V=IR

 

[hm12]

thank you! so negative gradient of B graph is induced E (similar to electric field strength being negative potential gradient huh?) how about the one i posted earlier than that?? (in the same page (75th)

Emf is the negative gradient of a flux time graph, magnetic flux density time graph and current time graph. Follow this and u can draw the other graphs too

 

[hm12]

Thanks for replying.. but can u plss tell me how did u find the original no. of undecayed nulei and how can u say 9 decayedinto Iron and 1 was left as manganese ?? if u dun mind then can u plss explain me in detail..

because the question says the ratio of iron/manganese is 9/1 so 9 decayed into iron and one was left total 9+1=10

 

[namename]

Emf is the negative gradient of a flux time graph, magnetic flux density time graph and current time graph. Follow this and u can draw the other graphs too

meaning that I/t,Φ/t and B/t are identical?
So does that give rise to phase difference of 90 degrees between I/t or Φ/t or B/t and Emf/t graph?

 

[m_tayyeb7]

hello can anyone help me out with (may/june 2007 Q3) how to find the area in this question???

 

[hm12]

meaning that I/t,Φ/t and B/t are identical?
So does that give rise to phase difference of 90 degrees between I/t or Φ/t or B/t and Emf/t graph?

yes they are all identical because emf=-delta Φ/t
yes there is a phase angle difference of 90 degrees

 

[Aahliya]

because the question says the ratio of iron/manganese is 9/1 so 9 decayed into iron and one was left total 9+1=10

Thanks for ur kind help..

 

[Aahliya]

CAN ANYONE SOLVE THIS ONE..

M/J 2006 (Paper 4)

Question (1)
b(i) Show that, for the rocket to travel from a height R to a height 2R above the planet’s
surface, the change ΔE(p.e) in the magnitude of the gravitational potential energy of
the rocket is given by the expression

ΔE(p.e) = GMm/6R