Calculate binding energy & compare to Electrostatic Repulsion

Smythe

4He2 has size of ~ 2 x 10^-15 m and a mass of 4.0015u. Calculate the binding energy of this nucleus, and compare it to the electrostatic repulsion of its constituents

For the first part I have calculated B.E. = 4.5 x 10^-12 J This agrees with my notes.

For the second part do I use the equation E = (q1 x q2) / [4∏(ε0)r^2]

Which would be;

(1.6 x 10^-19)^2 / [4∏ x 8.85 x 10^-12 x (1 x 10^-15)^2]

= 230 J

The reason I ask is because in the notes I have the r = 1 x 10^-15 value is not squared in the same calculation therefore giving an answer of 2.3 x 10^-13 J.

So I wasn't sure which is correct. Thanks for any advice!

Delphi91

Smythe wrote: »

For the first part I have calculated B.E. = 4.5 x 10^-12 J This agrees with my notes.

For the second part do I use the equation E = (q1 x q2) / [4∏(ε0)r^2]

Which would be;

(1.6 x 10^-19)^2 / [4∏ x 8.85 x 10^-12 x (1 x 10^-15)^2]

= 230 J

The reason I ask is because in the notes I have the r = 1 x 10^-15 value is not squared in the same calculation therefore giving an answer of 2.3 x 10^-13 J.

So I wasn't sure which is correct. Thanks for any advice!

The first answer is correct.

The equation in which r is not squared is the equation for the potential energy between the two charged particles.