# Having trouble understand the Mass-to-Charge Ratio

1. Oct 2, 2008

### Carlos508

I'm having trouble understanding how you would divide the charge of an object by its mass. How can you divide a charge - I mean isn't it either positive or negative? I understand that the charge is equal to the 6.25 × 1018 so an electron would have a charge of −1.602 x 10-19.

I guess my question is, how can you divide a charge by mass - isn't that like dividing apples and oranges? I understand that mass and energy are related, but I don't understand how you can divide a charge with a mass.

2. Oct 2, 2008

### tiny-tim

Welcome to PF!

Hi Carlos508! Welcome to PF!

In maths, you can divide anything by anything else, so long as you make it clear that the result is in "quotient units" …

for example, you can divide miles by hours, to get mph …

you can even divide money by minutes, to work out how fast you're spending …

and you can divide apples by oranges, so long as you make it clear that the result is not a dimensionless number, but is a number with dimensions apple.orange-1.

3. Oct 3, 2008

### Carlos508

Ah, of course. I can't believe I overlooked that, it makes sense to me now...so when you're dividing the charge by the mass, you're not necessarily trying to divide one into another (?), but determining the ratio between the two. Got it!

Thanks for your help, and the welcoming :)