By electrostatic induction, a charge of 10^-9 is induced on an insulated metal shpere. If this amount of charge takes 10^-3 s to flow through a galvanometer(a device for detecting and measuring a small current), calculate
(a) the average electric current indicated by galvanometer - ans : 10^-6 A
(b) the number of electrons that pass through the galvanometer per second. (take the charge carried by each electron as 1.6 X 10^-19
The method is 10^-6 C / 1.6 X 10^-19 C = 6.25 X 10^12
Does 10^6 C ^=10^6 A? If yes, alright. Otherwise, why did the question use 10^6 instead of 10^-9?
Thanks.
No. NO. NOOOOO
Use formula Q=It pls. where Q = charge, I = current, t = time.
Q = It
10^-9 = I x 10^-3
I = 10^-9 / 10^-3 = (using simple indices) = 10^-6 A
Is this your O level year btw? If so, you are in serious danger of getting screwed physics. Try memorising forumlae to the best of the ability. All the best.
EDIT: for the second part, use Q = Ne where Q = charge, N = number of electrons, e = electron charge.
So N = Q / e
Ok?
Originally posted by Garrick_3658:No. NO. NOOOOO
Use formula Q=It pls. where Q = charge, I = current, t = time.
Q = It
10^-9 = I x 10^-3
I = 10^-9 / 10^-3 = (using simple indices) = 10^-6 A
Is this your O level year btw? If so, you are in serious danger of getting screwed physics. Try memorising forumlae to the best of the ability. All the best.
EDIT: for the second part, use Q = Ne where Q = charge, N = number of electrons, e = electron charge.
So N = Q / e
Ok?
Eh no. The second solution is from the textbook. I thought there's something wrong with the explanation since it used 10^-6 and not 10^-9 (that's the main question i want to ask). The first question was merely there to guide you. (there's the answer just right beside the question if you didn't see)
Thanks anyway.
TS sounds right in his explanation. Anyway, my class stumbled upon this problem and we found something weird with this answer in the text. The text indeed said 10^-6 C passes through galvanometer in the question. Frankly, isn't 10^-6 referring to CURRENT in the first question? How can the explanation change it to charge in the second question?
Cheers.
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The SI unit for Charge is Coulomb (C)
The SI unit for Current is Ampere (A)
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Chapter 1 pls
EDIT: upon second look, maybe you are confused as in why an instrument used to measure current can measure charge. That's where your definitions come in (memorise as well. but i merely sort of "understand" it. i don't memorise science. pretty easy to "seep into brain" if you ask me)
Current is the flow of charge.
thanks Garrick for your help :D
allow me to put it in simpler terms
for part b, take note of the question
calculate the number of electrons that pass through the galvanometer per second.
Definition of ampere is amount of charges passing through per second.
So, 10^-6 A means 10^-6 C is passing through the galvanometer in 1 second.
That is why 10^-6 is used in the calculations :D
10^-6 C passes through per second
Means 10^-6 / (1.6 * 10^-19 C) electrons passes through per second
Hi everyone.
Your explanations prompted me to have this question in mind.
If charge is related to the current flow in the circuit. Then are we able to know how much current flows through a circuit by knowing the number of electrons flowing PER second? Take the value for number of electrons as 5 X 10^18 for example. Is it directly related to the charge?
Cheers! ^^
Originally posted by anpanman:Hi everyone.
Your explanations prompted me to have this question in mind.
If charge is related to the current flow in the circuit. Then are we able to know how much current flows through a circuit by knowing the number of electrons flowing PER second? Take the value for number of electrons as 5 X 10^18 for example. Is it directly related to the charge?
Cheers! ^^
Correct
You will see this quite often in A level physics
This is because the basic unit of charge is the charge of an electron: 1.602 * 10^-19 C
You cannot go any lower, and any charges you have will definitely be a multiple of the charge of an electron.
So I simply take 5 X 10^18 X 1.602 * 10^-19 to find the charge?
I find this unusual because we haven't been taught the value of charge of an electron before. Thank you.
The charge of an electron is a constant .
You need to use formula Q=IT.
Current is the movement of charges, and the charges are due to electrons.
=> the above is still part of O level physics