# Homework Help: Please help me,, Mastering physic rounding number

1. Mar 30, 2009

### cupcake

A photon of wavelength 4.38×10^−2 nm strikes a free electron and is scattered at an angle of 38.0 degree from its original direction.

Find the wavelength of the scattered light.
and my answer is this 4.43×10−2 nm (correct answer)

Find the change in energy of the photon.

E= hc / lambda1 = 1.24*10^-6 / (0.0438*10^-9) = 28310.50 eV

E= hc/ lambda2 = 1.24*10^-6 / (0.0443*10^-9) = 27990.97

and the change in energy is 319.529..
i have tried to enter 319 or 320 but mastering physic gave me

"Not quite. Check through your calculations; you may have made a rounding error or used the wrong number of significant figures."

***hate mastering physics...

2. Mar 30, 2009

### Redbelly98

Staff Emeritus

Since the wavelength was given to 3 significant figures, the energies are each known to 3 significant figures.

This makes the two energies accurate to the nearest ___ eV.

Does that help?

3. Mar 30, 2009

### cupcake

what did you mean by the nearest ____ eV??

so, what number should i enter?
320 and 319 don't help much...

i already lost some points because of it.. :(

4. Mar 31, 2009