Identical charges A, B, C, and D, each with a charge of magnitude 1.5 micro Coulomb, are situated at the corners of a square whose sides are 21 cm long. Two diagonally opposite charges are positive, the other two negative.
Calculate the net force acting on each of the four spheres.

Modern physics a photon emitted from an excited hydrogen atom has an energy of 3.02 electron volts. which electron energy-level transition would produce this photon? a. n=1 to n=6 b. n=2 to n=6 c. n=6 to n=1 d. n=6 to n=2 i chose b but the correct answer is d can someone tell me why? and what's the difference?

Which is a substance that can be separated by physical means and is not the same throughout

What about a rubber band, can it change its shape? is it a solid?