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Cheak Yin 發問於 科學及數學其他 - 科學 · 1 十年前

# 天同師兄,有關dc.motor,請回答

q:當coil既angular velocity等於V/BAN既時候, current會等於零.

### 1 個解答

• ?
Lv 7
1 十年前
最愛解答

Q: 個motor冇current都可以郁,power=i V,咁iput power除左starting motor果陣之外咪唔洗再input power?

Yes, you are right. This is really the case for an ideal motor under a "no load" condition. At starting, the motor acquires energy from the power source (e.g. battery), it retains that energy in rotation, because there is no dissipative force (such as friction). At this stage, the power source no long supplies any additional energy for the rotation of the coil. The coil rotates merely because of inertia. This is just like you push an object on a frictionless surface. Once you give it a push, the object goes at a constant speed withou the need

of any additional force.

Of course, such situation cannot occur in reality. No motor is ideal. At least, there is some frictional force on the axis of the motor that would dissipate the rotational energy of the motor coil. Hence, for a practical motor under a "no load" condition, there is a small current flowing through the coil providing a torque to balance the frctional force. The power source therefore needs to supply energy to keep the coil in rotation at a constant speed.

When there is a load applied to the motor, the resistance force acting on the coil increases. Under such condition, the current through the coil has to increase further in order to provide a larger torque to do mechanical work. Consequently, the power source needs to supply a larger current, hence a higher power, to keep the motor running.