举一反三
- A single phase ac induction motor has two windings, one is a run winding and the other is called a start winding. Strat winding can only work for a very short time to avoid overheated. A _____________ switch is installed inside motor to disconnect the strat winding when the motor speed reached 75% RPM.
- In typical induction motors, the stator winding is connected to the source and the rotor winding is short-circuited for many applications, or may be closed through external resistances. Herein, we can also call “stator winding” and “rotor winding” the ( ) respectively. A: field winding and armature winding B: armature winding and field winding C: armature winding D: field winding
- For 3-winding transformers, when we do the short circuit test, we can measure from winding 3, with winding 1 shorted and winding 2 open, then can get leakage impedance Z13 value. ( <br/>)
- 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
- What is the meaning of[img=31x25]17de809ba6b2a44.jpg[/img]?[img=362x202]17de809bb25fc43.jpg[/img] A: Permeability of the air gap B: Reluctance of the air gap C: Length of the air gap D: Length of the magnetic circuit
内容
- 0
A square current loop with length a on each side carries a current I. The loop is in a uniform magnetic field B. If the loop is in the stable equilibrium, the magnetic flux passing through the loop onlyby the uniform field is ( ). A: [img=30x22]1803a3748913c57.png[/img] B: 0 C: [img=44x24]1803a37490df0b1.png[/img] D: indeterminable
- 1
The title of the song “Everyday Is a Winding Road”is a metaphor.
- 2
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
- 3
Given that the magnetic circuit of DC electromagnet. The voltage U is constant . How will the Magnetic flux [img=13x19]1803a2fab6cb10e.png[/img] change when the air gap length increases ( ).[img=455x406]1803a2fac3677ca.jpg[/img] A: increase B: decrease C: remain unchanged D: not sure
- 4
Given that the magnetic circuit of AC electromagnet. The voltage U is constant . How will the Magnetic flux [img=13x19]1803a2fa8f20802.png[/img] change when the air gap length increases ( ).[img=455x406]1803a2fa9d5f73f.jpg[/img] A: increase B: decrease C: remain unchanged D: not sure