How many electrons make up a charge of -90.0μC ?

[Orhan]

It says in question "Express your answer using three significant figures."

Now;
I know
1e = 1,6*10^-19C
-90μC=-9*10^-5C
N=q/e

so

(-9*10^-5C)/(1,6*10^-19C)
=-5,625E+14 or -5,625*10^14

but that's a computer program so i don't know what it really wants from me
i don't know my answer is true or not. i really need some help

 

[gneill]

Hello Orhan,
Welcome to Physics Forums.

In future, please use the formatting template provided to format your question. It's in the rules.

It says in question "Express your answer using three significant figures."

Now;
I know
1e = 1,6*10^-19C
-90μC=-9*10^-5C
N=q/e

so

(-9*10^-5C)/(1,6*10^-19C)
=-5,625E+14 or -5,625*10^14

but that's a computer program so i don't know what it really wants from me
i don't know my answer is true or not. i really need some help

Note that the charge on an electron is negative. The e you've used is just the magnitude of that charge, so be sure to include the correct sign! You should end up with a positive number for the number of electrons.

Note also that they are asking for three significant figures. The value of e that you've used contains only two! So find (look up) a better value for e.

 

[Orhan]

Hello Orhan,
Welcome to Physics Forums.

In future, please use the formatting template provided to format your question. It's in the rules.Note that the charge on an electron is negative. The e you've used is just the magnitude of that charge, so be sure to include the correct sign! You should end up with a positive number for the number of electrons.

Note also that they are asking for three significant figures. The value of e that you've used contains only two! So find (look up) a better value for e.

I searched from the net it says
1e = 1.60217646e-19C
so 1,60 is its 3 digit version and it equals 1,6. I thought that way. And yeah i fixed the -/+ problem but still not true

 

[gneill]

I searched from the net it says
1e = 1.60217646e-19C
so 1,60 is its 3 digit version and it equals 1,6. I thought that way. And yeah i fixed the -/+ problem but still not true

When you have constants in your calculations (like pi, or e, or the charge on an electron), it's always better to use values with more significant figures than the number of figures in your other data. Don't trim or round intermediate values n your calculation steps, otherwise rounding or truncation errors will creep into your significant digits.

Now, what do you mean by "still not true"? What is your current result?

 

[Orhan]

When you have constants in your calculations (like pi, or e, or the charge on an electron), it's always better to use values with more significant figures than the number of figures in your other data. Don't trim or round intermediate values n your calculation steps, otherwise rounding or truncation errors will creep into your significant digits.

Now, what do you mean by "still not true"? What is your current result?

Sorry for my bad English but i don't know if i understood true. u mean use "1e = 1.60217646e-19C" in your calculations and express your result after all the calculations finished, right ?
Edit : i just changed - to + nothing more :)

 

[gneill]

Sorry for my bad English but i don't know if i understood true. u mean use "1e = 1.60217646e-19C" in your calculations and express your result after all the calculations finished, right ?
Edit : i just changed - to + nothing more :)

Well, if you're going for 3 significant figures in your you might want to use 5 for your constants.

The numerical value that you presented initially (ignoring the sign) was not specified to three significant figures (it was specified to four, and they were not accurate to four!).

Also, Orhan, please note that text-speak abbreviations like "u" for "you" are not allowed on the Forums.

 

[Orhan]

Well, if you're going for 3 significant figures in your you might want to use 5 for your constants.

The numerical value that you presented initially (ignoring the sign) was not specified to three significant figures (it was specified to four, and they were not accurate to four!).

Also, Orhan, please note that text-speak abbreviations like "u" for "you" are not allowed on the Forums.

sorry for abbreviation.
I'm doing everything and finding the result = 5,62*10^14 or 5,62E+14
and i just want to be sure 1,23 has 3 significant figures right? or should it be 1,234?

 

[gneill]

sorry for abbreviation.
I'm doing everything and finding the result = 5,62*10^14 or 5,62E+14
and i just want to be sure 1,23 has 3 significant figures right? or should it be 1,234?

Three figures means three digits. So 1,23 has three significant digits.

Your value 5,62*10^14 looks good. Now, I don't know where the computer program that you're using was authored, but be sure to confirm that it accepts a comma as a decimal point for numeric values. You'll have to read its documentation to find out how to specify entries that require scientific notation.

 

[Orhan]

Three figures means three digits. So 1,23 has three significant digits.

Your value 5,62*10^14 looks good. Now, I don't know where the computer program that you're using was authored, but be sure to confirm that it accepts a comma as a decimal point for numeric values. You'll have to read its documentation to find out how to specify entries that require scientific notation.

Thanks for help i entered 999 times 5,62*10^14 because in lessons we use ",". But i changed with "." and it said to me correct.