Video Transcript
What is 30 kiloelectron volts in
joules?
In this exercise then, we’re
converting an amount of energy from one unit, kiloelectron volts, into another,
joules. To get started doing this, we can
recall just how many joules of energy are in one electron volt. A single electron volt is equal, to
three decimal places, to 1.602 times 10 to the negative 19th joules. In our given energy value though,
we see that we’re not only working with electron volts but rather kiloelectron
volts. This letter k is what’s called a
unit prefix. And we can recall that it
represents a kilo of whatever unit is involved, which means 10 to the third or 1000
times that unit. So then a kiloelectron volt is 1000
volts.
Knowing this, we can rewrite our
energy value in units simply of electron volts. It’s 30 times 10 to the third
eV. In doing this, we’ve accounted for
our unit prefix kilo-. And now we have a straight line of
sight into converting our energy from electron volts into joules. The way we’ll do this is we’ll
multiply our energy by a fraction. The denominator of that fraction
will be one electron volt. We do this so that when we multiply
through, the units of electron volts cancel out. And the value we’ll use in our
numerator is 1.602 times 10 to the negative 19th joules. Note that this is equal to one
electron volt.
When we carry out this
multiplication, we’ll get a result in units of joules. And in doing this, if we keep two
significant figures in our final answer because we were given an energy originally
with two significant figures, then we find a result of 4.8 times 10 to the negative
15th joules. That’s 30 kiloelectron volts in
joules.
