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A2 Physics - charge question

An electron beam carries a current of 1.5mA and scans a TV screen 25 times per second.
i) Calculate the charge transferred onto the screen during one complete scan.
Q = It = 1.5x10^-3A x 1/25s = 6 x 10^-5C

ii) If the screen has an area of 1220cm^2, calculate the number of electrons transferred to each mm^2 of the screen. The charge of the electron is 1.6 x 10^-19C

Charge per cm^2 = 6 x 10^-5/1220 = 4.918 x 10^-8 Ccm^-2
Charge per mm^2 = 4.918 x 10^-8 Ccm^-2/100 = 4.918 x 10^-10 Ccm^-2
Number of electrons per mm^2 = 4.918 x 10^-10 Ccm^-2/(1.6 x 10^-19C) = 3.07 x 10^9 electrons per mm^2

However the answer in the book is 3.07 x 10^6

Can someone see if i've gone wrong anywhere?
Reply 1
Avatar for tomtheone
tomtheone
2
Wouldn't you have a better chance of someone answering if you were to put it in the physics section.
Reply 2
Avatar for BCHL85
BCHL85
12
I don't find any mistake :smile:
tomtheone
Wouldn't you have a better chance of someone answering if you were to put it in the physics section.

You'd be surprised actually. :rolleyes:

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