Physics, Chemistry and Biology: Post your doubts here!

[Iridescent]

i thought copper is a good conductor so the paper should turn Brown
Thanks

As it is a good conductor, the heat does not stay there but gets conducted away.

 

[fatima hussein]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_s11_qp_12.pdf
Q 1 - d = 330*0.4 = 132...but as the sound reflects back (echo) it covers 2 equal distances - one from bat to wall and the other from wall back to the person!..so divide the d by 2 to get the distance to wall.
Q 8 - 'some ice has melted'....the others still remains...also 'what is the temperature of the remaining ice' indicates that it should be A 0 C..ice cannot be present in 2 4 or 8 degree C
Q 10 - the best conductor of heat will conduct heat more efficiently and melt the more wax...hence less balls should be left!...ans opt A
Q 17 - work done = force * distance ...( niether the force nor the distance to lift the hays have changed)..so W = same but as P = W/T...so as the work done is same but time is less...hence power will increase!
Q 18 - ans should be B...all other methods use the speed of water(current)
Q 23 - should be D ....frequency doesnt change ever....in dispersion of light..the darker the colour the less they are refracted..refraction occurs because of the speed difference...
Q 24 - C as it is a fact...look out for the definition of wavefront
Q 27 - C or D...most probably C as i heard capacitors store energy...but it hence stores current as well..capacitors are used in time delay ...ex - light in weedings..goes on and off!
Q 29 - it is given that as temp increases R decreases..so R will decrease as well as V ( V proportional to R ...since I in series circuit is same everywhere!)
Q 31 - can be D...as I after flowing through Z can flow through Y and again through Z...but i am confused...as due to excess current the lamp should go off!
Q 34 - should be D...'step down transformer'....more turns in primary and less turns in secondary!
Q 35 - both circuit breakers and fuse have same function...so should be B
Q 37 - should be C...hl = initial amount * (1/2)^n.... where n =no. of half lives!
i am not sure about any of the ans!...i am from GCE o level...but still practising ur Qs as tomorrow i have physics...so r my ans correct!??

Thank you so much!!! you took the time to answer my questions with explanation and got them correct

 

[fatima hussein]

I keep asking questions but i really need help
Can someone explain question 38 in: http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_w08_qp_1.pdf

 

[princess sofia]

hey I have just started chem , after a whole year , can anyone tell me why is it ethanol , the mcq is
in which substance are the particals furthest apart at room temperature
a. ethanol
b. methane
c. salt
d. suger
, I know dat salt n sugar are solids so these r excluded but methane is gas so why not thx

 

[fatima hussein]

i remember this question in http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf its question 1

the answer is B methane. you must have read the mark scheme wrong.http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_ms_1.pdf

 

[sourov97]

I keep asking questions but i really need help
Can someone explain question 38 in: http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_w08_qp_1.pdf

Thanks!...but my physics didnt go as i expected!..
- half life is the time needed to time need to the radioactive substance to be halved!...so see..initially the reading was 140 counts...so half of it should be 70 counts.
now from the table...after 40 sec the count was 82 but after 60 sec the count was 61...which means that 70 counts must be in between 40 and 60 secs!..so B

 

[fatima hussein]

Thanks!...but my physics didnt go as i expected!..
- half life is the time needed to time need to the radioactive substance to be halved!...so see..initially the reading was 140 counts...so half of it should be 70 counts.
now from the table...after 40 sec the count was 82 but after 60 sec the count was 61...which means that 70 counts must be in between 40 and 60 secs!..so B

Thanks So Much. I'm Really Sorry To Hear About That. But You Know You Could Have Done Good But Your Not Sure Of Your Answers.

 

[kiara15]

can any1 guide me how to calculate absolute errors in gradient and y intercept? alsoow to how to draw worst fit line in graph? plzz

 

[princess sofia]

i remember this question in http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf its question 1

the answer is B methane. you must have read the mark scheme wrong.http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_ms_1.pdf

oopes thnx , cn u tell me how like the theory behind it ,

 

[Iridescent]

hey I have just started chem , after a whole year , can anyone tell me why is it ethanol , the mcq is
in which substance are the particals furthest apart at room temperature
a. ethanol
b. methane
c. salt
d. suger
, I know dat salt n sugar are solids so these r excluded but methane is gas so why not thx

Methane.

 

[Iridescent]

oopes thnx , cn u tell me how like the theory behind it ,

Methane is a gas, ethanol is a liquid while the other two are solids. In gases, the molecules are furthest apart compared to solids and liquids.

 

[sourov97]

Thanks So Much. I'm Really Sorry To Hear About That. But You Know You Could Have Done Good But Your Not Sure Of Your Answers.

i meant...i may loose 1-2 marks in paper 1(mcq) and max 8-10 marks in P2(theory)...just could confirm 2 marks loss in P2...maybe i still have an A but just miss the A*

 

[princess sofia]

Methane is a gas, ethanol is a liquid while the other two are solids. In gases, the molecules are furthest apart compared to solids and liquids.

o thnk I thought ethanol was a gas thnx for clearing it

 

[Iridescent]

o thnk I thought ethanol was a gas thnx for clearing it

Ethanol is ethyl alcohol which is a liquid.

 

[Sami Imran]

Thank you so much!!! you took the time to answer my questions with explanation and got them correct

hmmm!... Iridescent and ZaqZainab aslo helped...so dont u want to thanks them as well..specifically.

 

[fatima hussein]

w11:
Q11: This is because pressure and volume are inversely proportional if temperature is kept constant. If the volume is decreased, the pressure will increase....

Thanks Very Much For Explaining It and taking the time to answer

 

[fatima hussein]

hmmm!... Iridescent and ZaqZainab aslo helped...so dont u want to thanks them as well..specifically.

He was the first one i saw and i didnt have time to reply to them.... -___-

 

[fatima hussein]

Okay so firstly i would ask yo not to write with that many spaces my dear!!
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_w11_qp_12.pdf
11the less the volume the more the pressure so by time the volume increases , it increases in B and in C but they have said they measured the pressure in the starting which means 0 time the pressure is already what is in the cylinder.....

THANKS SO MUCH!! FOR THE LINK AS WELL. ITS OKAY, I'll Try to figure it out myself.

 

[ZaqZainab]

so you did find some time out?
you are welcome and figure out what?

 

[GorgeousEyes]

Please june1990 no.8 . 30 . 31 and 38 .