How dc motor starts?

Answer 1

You mean how does it start spinning from a stop? When electricity is applied to it there is a magnetic field created in the copper windings and iron or steel they are wound around which are located in the center of the motor. If you've ever played with magnets you know they attract or repel depending on their relation to each other. There are magnets in the outer edge of the body of the motor too, so by creating one magnetic field using electricity in the core, it will react with the magnets on the outer edge of the case and they will push and/or pull against each other. They're set up or timed so the electric magnetic field will react with the magnet on the outside thus turning the core closer or away from the outer magnet, then the power is cut and applied to another winding in the core that is at a different angle but since the core has moved now the that next winding is in position to react with the outer magnet and repeat the process. So using these magnetic fields powered by electricity and timed to react with each other you'll get a steady spin out of it which is the whole point. The more powerful the outer magnets and the more powerful the electromagnets in the core will result in a more powerful motor. Btw, the electro magents can be on the outside and regular magnets on the inside, but it's just easier to make with the elect mags in the core. You can even make both sets electromagnets if you like, this is how alternators on cars are made except an alternator or generator makes electricity from a spinning power source rather than a motor which uses electricity to make spinning power. They're very similar in design and many electric motors can be used as generators with no modification at all! A toy car for example that goes when a battery is attached could also charge the battery if you pushed the car along yourself.

I hope this makes sense.