Ampere's law, Biot-Savart law and E-field questions

[gambit1414]

Hi,
1. Generally when using Gauss's law to e-field, I'm aware that the the surface you chose must be symmetrical and E-field is constant therefore you would only use Gauss's law for infinite sheets of charge, spherical distribution of charge and infinite line charge am i right?

2. Regarding ampere's law, I'm aware that we use this when the B-field is constant does this only the direction is not changing? (eg. for a circular loop it will always point in the (phi) direction). A follow up on this question, for a square loop how does the b-field look like.

3. Lastly, we would use biot-savart law over amperes law in any case we aren't dealing with a current carrying wire, am i right?

I have an exam next week on this stuff, and i just want to make sure i have the theory right because that's what I'm confused about, the calculus bit will easily fall in place once the theory is clear. Thank you for any help.

 

[NateD]

1. Yes, you are correct. Gauss's law can be used to calculate the electric field in situations such as those you mentioned. 2. Yes, Ampere's law is used when the magnetic field is constant in direction. For a square loop, the B-field points in the same direction around the loop; this direction is perpendicular to the plane of the loop, and the magnitude of the B-field is proportional to the net current through the loop.3. Yes, Biot-Savart law is used when we are dealing with currents that are not in the form of a wire.