How many electrons would transfer 1 J of energy to a screen?

  • Thread starter CivilSigma
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  • #1
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An elecetron has a mass of 9.11 * 10^-31 kg. If it moves across a television picture tube at a speed of 5.0 * 10^5 m/s. Calculate:
a) it's kinetic energy
b)how many such electrons would transfer 1 J of energy to the screen.
My answer to a) is 1.14 * 10^-19 J, which is correct.
My answer to b) is 1.14 * 10^19, which is not correct. The correct answer is 8.8 * 10^18. How did they get that? because if 1 electron has 1.14 * 10^-19 J then wont we need 1.14 * 10^19 electrons for 1 J ?
 

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  • #2
gneill
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My answer to a) is 1.14 * 10^-19 J, which is correct.
My answer to b) is 1.14 * 10^19, which is not correct. The correct answer is 8.8 * 10^18. How did they get that? because if 1 electron has 1.14 * 10^-19 J then wont we need 1.14 * 10^19 electrons for 1 J ?
Changing the sign of the exponent is not the same as division... What about the mantissa of the number?
 
  • #3
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om >.< I know what i did wrong!!!!!!! Stupid mistake. Thanks for that comment.
 

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