Biology; Chemistry; Physics: Post your doubts here!

[Amnaa]

Background count = constant = 10 counts/min.
So, Radioactive source count = 400 counts/min.
After three half lives, the radioactive source count = 400/8 = 50 counts/min.
After 15 days, the count rate = 50 + 10 (b.c) = 60 counts/min. C.

400 ko 8 se kiu divide kiya??

 

[Saad Mughal]

400 ko 8 se kiu divide kiya??

This is kinda basic logic, but there is a formula behind it too; it is.
Radioactive substance remaining = Original amount of substance * (1/2) ^ n, where n = number of half lives.

 

[Amnaa]

http://papers.xtremepapers.com/CIE/Cambridge%20International%20O%20Level/Physics%20(5054)/5054_w12_qp_11.pdf

question no.7 why the answer is not C..
400*12=4800 and 300*16=4800

 

[farhan141]

http://papers.xtremepapers.com/CIE/Cambridge%20International%20O%20Level/Physics%20(5054)/5054_w12_qp_11.pdf

question no.7 why the answer is not C..
400*12=4800 and 300*16=4800

Should be C. Marking Scheme is wrong here.

 

[Saad Mughal]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w12_qp_11.pdf

question no.7 why the answer is not C..
400*12=4800 and 300*16=4800

It is C.

 

[Amnaa]

http://papers.xtremepapers.com/CIE/Cambridge%20International%20O%20Level/Physics%20(5054)/5054_w12_qp_11.pdf

please do question no. 9 for me..

 

[sourov97]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w12_qp_11.pdf

question no.7 why the answer is not C..
400*12=4800 and 300*16=4800

the answer is C!..in markscheme!

 

[Saad Mughal]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w12_qp_11.pdf

please do question no. 9 for me..

"length of 9cm WHEN loaded with a 200g mass".
So, original length of spring = 9 - 2 = 7 cm.
With 100g mass, length of spring = 7 + 1 = 8 cm.

 

[sourov97]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w12_qp_11.pdf

please do question no. 9 for me..

the graph shows when the load is 200 the extension is 2 cm....and the total length of spring is 9cm...so the length of spring should be 9-2 = 7cm
then from the graph the extension for 100g is 1 cm...therefore total length = 1 + 7 = 8

 

[Amnaa]

the answer is C!..in markscheme!

hahaha yes it is
my bad

 

[Amnaa]

"length of 9cm WHEN loaded with a 200g mass".
So, original length of spring = 9 - 2 = 7 cm.
With 100g mass, length of spring = 7 + 1 = 8 cm.

i was referring to the wrong marking scheme

 

[Saad Mughal]

i was referring to the wrong marking scheme

Oh.

 

[Zuhsid]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w12_qp_11.pdf

please do question no. 9 for me..

Looking at The graph, it means that at 200g load, the extension is 2cm, where as on the other drawing, the lenght is 9cm, this means that the spring's actual length is 7cm( as if we add 2cm of extension, it would be 9cm).......
So if 100g is placed, the extension is 1cm, hence the total length would be 7+1..... 8... so B is your answer...
Hope it helps...

 

[papajohn]

Any guess paper for Physics??

 

[Amnaa]

under which topic the sensitivity of thermometer is covered?

 

[Saad Mughal]

under which topic the sensitivity of thermometer is covered?

What do you mean? In the syllabus, it comes under Temperature.

 

[Amnaa]

What do you mean? In the syllabus, it comes under Temperature.

kya app ke pass notes hain... is topic se related.. like which one is better to use like .. thin bulb aur thicker one?

 

[Saad Mughal]

kya app ke pass notes hain... is topic se related.. like which one is better to use like .. thin bulb aur thicker one?

I don't have notes, but I'll tell you. There are 2 things to consider for thermometers, one is responsiveness and one is sensitivity.
-Responsiveness is how quickly the thermometer responds to a temperature range.
-The sensitivity is how big a change is there (for example in volume of mercury) for a change in temperature.
-A thin bulb conducts the heat from surroundings quickly so it is used to increase responsiveness.
-The volume of liquid should be less so that the liquid expands and reacts to the temperature change quickly.
-For sensitivity, a narrow bore (inner line) of thermometer is used so that the expanded liquid travels further for a little change in temperature.
-A liquid that expands quite a lot for a temperature change is used to increase sensitivity.
Other than that you need to know what linearity is; it is when a liquid expands UNIFORMLY for a change in temperature.
P.S. Keep in mind that increasing the sensitivity decreases the range of a thermometer.

 

[Amnaa]

When one radium nucleus decays, its mass decreases by 8.8 × 10–30 kg.
How much energy is equivalent to this loss in mass?
(speed of light c = 3.0 × 108
m/s)
A 6.8 × 10–42 J B 2.6 × 10–21 J C 4.0 × 10–13 J D 7.9 × 10–13 J

 

[passion hunter]

I don't have notes, but I'll tell you. There are 2 things to consider for thermometers, one is responsiveness and one is sensitivity.
-Responsiveness is how quickly the thermometer responds to a temperature range.
-The sensitivity is how big a change is there (for example in volume of mercury) for a change in temperature.
-A thin bulb conducts the heat from surroundings quickly so it is used to increase responsiveness.
-The volume of liquid should be less so that the liquid expands and reacts to the temperature change quickly.
-For sensitivity, a narrow bore (inner line) of thermometer is used so that the expanded liquid travels further for a little change in temperature.
-A liquid that expands quite a lot for a temperature change is used to increase sensitivity.
Other than that you need to know what linearity is; it is when a liquid expands UNIFORMLY for a change in temperature.
P.S. Keep in mind that increasing the sensitivity decreases the range of a thermometer.

wah kya summary thi....itna acha explain kisi book mein nahi....