# Homework Help: How to read this equation

1. Apr 13, 2012

### Alouette

Just having trouble determining what they mean by "The charge to mass ratio for a singly ionized benzene molecule is e/(78u)=1235712.07908557C/kg."

For this, what would be the charge and what would be the mass?

2. Apr 13, 2012

### Staff: Mentor

The single charge is a fundamental charge (equal to that on a proton, since 'singly ionized' means that the molecule has lost a single electron). The mass unit is an amu: atomic mass unit, also known as a dalton. Equivalent to 1.660538921 x 10-27 kg.

3. Apr 13, 2012

### Alouette

I see. So to clarify q = 1.602 x 10-19 & m = 78*u = 1.295 x 10-25?

4. Apr 13, 2012

### Staff: Mentor

Those are the numbers.

5. Apr 13, 2012

### Alouette

But where does that large given number come in?

6. Apr 13, 2012

### Staff: Mentor

I have no more information than what you stated in the first post. Where did you get the number, and in what context?

7. Apr 13, 2012

### Alouette

Ah well I figured it out, what they mean is e/m = charge to mass ratio. The context doesn't add much to figuring out what it means however, it just sets up the question.

As in every time e/m is encountered for the rest of the question, 1.26 x 106 (the long number of C/kg units) would be its value, which makes sense since it is asking for charge over mass. Kind of tricky too though...

I had initially thought we needed to find the individual values of q and m, which is why I asked where the large number came into play. Thanks for the info about amu though!

Last edited: Apr 13, 2012