# Number of electrons leaving crystal surface. any help ?

1. Apr 7, 2009

### CharS

number of electrons leaving crystal surface. any help :)?

1. A scanning tunnelling electron microscope (STM) measures a tiny electrical current tunnelling out of the surface of a crystal. The current is 0.30 pA (0.30 x 10-12 A).

Calculate the number of electrons per second leaving the surface of the crystal.

2. mass of an electron = 9.11 x 10-31 kg
charge of an electron = -1.6 x 100-19 C

3. I have no idea how to answer this. Thanks to anyone who has any tips or pointers :) or can show me how to work it out correctly! x

2. Apr 7, 2009

### LowlyPion

Re: number of electrons leaving crystal surface. any help :)?

Welcome to PF.

Neither the mass nor the charge is that useful for this. You need to look at the definition of an Ampere, which is 1 Coulomb/sec.

A Coulomb relates to a quantity of charges. Just look it up and calculate the rest.

3. Apr 7, 2009

### CharS

Re: number of electrons leaving crystal surface. any help :)?

thank you for your help :)

I looked it up before with little success!

so would the answer be = (0.30 x 10^-12) x (6.241 509 629 152 65 × 10^18)

??

i must look incredibly stupid! just never been taught this before, finding it really hard to learn myself x

4. Apr 7, 2009

### CharS

Re: number of electrons leaving crystal surface. any help :)?

oh wait.

i think it's 0.30 x 10^-12/ 6.24150948×10^18

before was wrong. is that the correct calculation?x

5. Apr 7, 2009

### LowlyPion

Re: number of electrons leaving crystal surface. any help :)?

When you do the math it will be.

You can simplify the number of digits needed however:

(0.30 x 10-12) x (6.24 × 1018)

6. Apr 7, 2009

### CharS

Re: number of electrons leaving crystal surface. any help :)?