Edexcel PHYSICS Doubts

[studz]

This is because you made two readings before calculating the answer. I've not read the question but am pretty sure there was something like initial and final readings.

Since two readings were made, same uncertainty was carried out twice. That's why we multiply it by two

Hope it helps

i dont get it where did we take two readings 
we just had a table of values for time in secs.

[Nobody]

then shouldnt the uncertainty be 0.01 because the values they give are 18.66 and 18.46 they can only read it upto 0.01?
sorry by the way im just panicking here thats y im pressing on it so much

look, let's take random values from a meter rule
ALL in CENTIMETRE
56.7
43.6
34.6
1.7
09.7
99.9

now, have a look. 56 CM & 7 MM
so, the smallest value is "*.X"
so, that .X will be 0.1 and not any less.
you can't read "26.77" cm on a meter rule. that's impossible value to get.

[Deadly_king]

In order to measure the time taken, we need to take two readings.

!st reading : 0.00
2nd reading : 3.02

So we got the same uncertainty twice

Same applies for the other measurement

[Dangerous99]

look, let's take random values from a meter rule
ALL in CENTIMETRE
56.7
43.6
34.6
1.7
09.7
99.9

now, have a look. 56 CM & 7 MM
so, the smallest value is "*.X"
so, that .X will be 0.1 and not any less.
you can't read "26.77" cm on a meter rule. that's impossible value to get.

I get what u mean. 0.1 is the uncertainty on the meter rule rite?
but the question I was doing they give the values 18.66 and 18.64 so obviously they can can only read it upto 0.01 sig figures, what will the uncertainty be in this case?

[Nobody]

I get what u mean. 0.1 is the uncertainty on the meter rule rite?
but the question I was doing they give the values 18.66 and 18.64 so obviously they can can only read it upto 2 DECIMAL PLACES, what will the uncertainty be in this case?

yes!
yes! It will be 0.01.
boy, you're smart!  

significant figures & decimal place are two different things

[Nobody]

even i dint get where did they bring 0.5 from

anyway guys can you list out the uncertainties of measurement of the following apparatus?
1. metre rule
2. voltmeter (not digital)
3. ammeter (not digital)
4. voltmeter (digital)
5. ammeter (digital)
6. Digital stopwatch
by the way, is human error an uncertainty too? Is human error 0.01s?
If it is, then please consider this case:
when a ball is allowed to free fall for 2s, the distance is recorded. (different sizes of ball are used) the distance has an uncertainty, however the uncertainty is human error (0.01s+0.01s) or uncertainty of the metre rule (0.5mm+0.5mm)?

thanks 

1. metre rule > 1 millimeter
2. voltmeter (not digital) >
it depends on the instrument that you use.
here it will be 10V
here it will be 2V
just measure the smallest value in the instrument.
that's the uncertainty

3. ammeter (not digital) >
again depends..
here it will be 2 A


4. voltmeter (digital) > if you read "5.034" uncertainty is "0.001 A" if you read "50.34" uncertainty is "0.01 A" ans so on
5. ammeter (digital) > same a above. ^^
6. Digital stopwatch > 0.1 second

[Dangerous99]

yes!
yes! It will be 0.01.
boy, you're smart!  

significant figures & decimal place are two different things

okai u know what? im feeling really dumb rite now cos according to what u just said the uncertainty is 0.01 not 0.5 like the mark scheme says.

[Assi1993]

Uncertainties in some instruments:

    * Stopwatch: 0.2 secs
    * Metre rule: 1mm
    * Vernier caliper: 0.1mm
    * Micrometer: 0.01mm
0.1 for the voltmeter

[Assi1993]

okai u know what? im feeling really dumb rite now cos according to what u just said the uncertainty is 0.01 not 0.5 like the mark scheme says.

which question,paper?? i want to check what it is

[Romeesa-Chan]

Please help me with the last question part d!  

[Nobody]

Uncertainties in some instruments:

    * Stopwatch: 0.2 secs
    * Metre rule: 1mm
    * Vernier caliper: 0.1mm
    * Micrometer: 0.01mm
0.1 for the voltmeter

stop watch : 0.1 seconds. >>sure
Vernier caliper: 1mm
Micrometer: 0.1mm  

[Dangerous99]

which question,paper?? i want to check what it is

question 2c page 29

[Assi1993]

Please help me with the last question part d!  

u have 2 just find the gradient!!
rearranging the equation gives us,
lnA=-ux+lnAo
y   =mx+c

-u is the gradient ...which u can find...
take a larger gradient triangle always...
so take the 1st plotted value and the last 1...
In this, u can take the coordinates(0,6.869) and (31.74, 5.257)

[Romeesa-Chan]

u have 2 just find the gradient!!
rearranging the equation gives us,
lnA=-ux+lnAo
y   =mx+c

-u is the gradient ...which u can find...
take a larger gradient triangle always...
so take the 1st plotted value and the last 1...
In this, u can take the coordinates(0,6.869) and (31.74, 5.257)

I got it. I am not sure whether my graph is right. Can you lemme know if it's right if I post a picture of it? Please?

[Dangerous99]

omg i just asked this super genius guy who i feel like marrying rite now By the way, he says the uncertainty is in fact 0.01 but due the fact that reaction time is also involved we take uncertainty as 0.5 (due to human error and because 0.5 is greater than 0.01)
So its 0.5/18.64 x 100%