eV to joule Conversion

Here an examples how to convert the unit of energy in eV to joule. Some questions do need this conversion to get the result.

5 MeV = .... joule

You knew already that M mean Mega = 10⁶ , and eV is electronvolt.

Take an attention that
1 eV = 1,6 x 10⁻¹⁹ joule

So then we have

5 MeV = 5 x 10⁶ x 1,6 x 10⁻¹⁹ joule
5 MeV = 8 x 10⁻¹³ joule
 

Converting kWh to joule

How we convert the unit of kWh to joule?
For instance a lamp uses 6 kWh of electric energy. How we convert it in joule?
kWh means kilo watt hour and 1 kilo watt means 1.000 watt and 1 hour means (60x60) second. So then
5 kWh = 5 x 1.000 x 3.600 = 18.000.000 joule
or for simplicity just multiply with 3.600.000
another
12 kWh = ...... joule
the answer
12 kWh = 12 x 3.600.000 = 43.200.000 joule

How about joule to kWh?
72 MJ = ..... kWh

Answer
MJ means mega joule, where 1 MJ = 1.000.000 joule
so then we have
72 MJ = (72 x 1.000.000) : 3.600.000
= 20 kWh

Calorie or Calories

Teacher : Today we'll learn energy, do you know what is the unit of energy?
Student : joule sir!
Teacher : Another possible unit?
Student : Calorie sir?
Teacher : You have 5 joule of energy. Could you convert in calorie?
Student : Yes sir, 1 joule = 0.24 calorie or 1 calorie = 4.2 joule so then I have 5 x 0.24 = 1.2 calorie of energy.
Teacher : 1.2 calorie or 1.2 calories ?
Student : 1.2 calorie sir, if we use 1.2 calories for expressing that, the "s" in physics mean second sir, so I think its better to use 1.2 calorie than 1.2 calories to avoid wrong interpreting.
Teacher : Ok, enough for today see you tomorrow, don't forget to bring your homeworks!