yup more physics, electrons and charge etc

A polythene rod was negatively charged by rubbing it with a cloth. The rod was then stroked several times across the metal cap of a meter used for measuring charge.
The initial reading on the meter was zero.

After 3.8s the final reading was -6.4 x 10^-8C

Calculate the number of electrons that were transferred to the metal cap.

please in english describe and explain how to do this question pleas epleas epleas¬

Reply 1

BCHL85

Q = n.e where Q is -6.4x10^-8C
e is -1.6x10^-19 (charge of electron)
-> n = Q/e.

Reply 2

john !!

-6.4 x 10^-8 C of charge was passed through

one electron has a charge of -1.6*10^-19
n electrons have a combined charge of (n)(-1.6*10^-19)

put this equal to the charge difference over the 3.8s:

(n)(-1.6*10^-19) = (-6.4 x 10^-8)
n = (-6.4 x 10^-8)/(-1.6*10^-19)
n = I don't have a calculator, but somewhere in the order of 10^11 electrons

as an extension, can you calculate the current?

Reply 3

Alice2411

no i cant but thansk nayway

Reply 4

elpaw

Alice2411

no i cant but thansk nayway

I = Q/t

Reply 5

habosh

ok in english
the charge of one electron is -1.6*10^-19
the total charge gained by the metal cap is -6.4*10^-8
to find number of electrons logicly you devide the total charge over the charge of one electron like if you have a basket full of apples and you want to know how many apples are there in the basket and you have a balance you find the mass of the all apples and basket and find a mass of one apple and devide the small mass from the big mass (assume that the basket has zero mass and that the apples have equal masses)
so you get the answer 4*10^11 or 400000000000