The type of field generated by a DC tacho-generator is A: pulsating magnetic field B: static field C: rotating field D: do not need field

What can be said about the field A: The field is left unplanted. B: The field is lying waste. C: The field is left open to playing. D: The field is played with this year,

The curl equation [img=154x44]1803a2a153c85f5.png[/img]shows that : A: The time-varying magnetic field can generate an electric field, in which the elecric field lines is closed around the magnetic field line. B: The time-varying magnetic field can generate a magneitc field, in which the magnetic field lines is closed around the electric field line. C: The magnetic field lines is closed themselves. D: Flux continuity

The difference in depth of field produced by between 85mm lens of the medium camera and of 135 camera is ______. A: no difference B: The depth of field by 135 camera is shallower. C: The depth of field by the medium camera is shallower. D: The depth of field by 135 camera is deeper.

The Biot-Savart Law is used to（ ） A: determine the magnetic field created by an electric current B: determine the electric field created by an electric current C: determine the force field created by an electric current D: determine the magnetic field created by individual point charges E: determine the electric field created by individual point charges

The<br/>magnetic field lines are used to visually describe the distribution<br/>of the magnetic field around the magnet. For the following<br/>statement,( <br/>) is wrong. A: Each<br/>magnetic field line is a closed loop curve B: No<br/>two magnetic field lines can cross each other C: The<br/>length of the magnetic field line reflects the strength of the<br/>magnetic field D: The<br/>tangential direction of any point on any of the magnetic lines is the<br/>direction of the magnetic field at that point

A circular loop of wire is held in a uniform magnetic field, with the plane of the loop perpendicular to the field lines. Which of the following will not cause a current to be induced in the loop? A: crushing the loop B: rotating the loop about an axis perpendicular to the field lines C: keeping the orientation of the loop fixed and moving it along the field lines D: pulling the loop out of the field

In the vector field, the vector line is such a curve where ( ) A: The tangent direction at each point on it is orthogonal to the direction of the vector field at that point. B: The tangent direction at each point on it is parallel to the direction of the vector field at that point. C: The value of each point on it is equal to the value of the vector field at that point. D: The vector line is the geometric curve of the vector field function.

场论可以分为classic field theory和quantum field theory

There is no magnetic field in an ideal conductor, but there is a magnetic field inside because of the surface current。