when the speed of a dc motor increase the armature current

A motor has an armature resistance of 4 ohm. On a 240 V supply and a light load, the motor speed is 200 rpm and the armature current is 5 A Calculate the motor speed at a full load. When armature current is 20 A.

The ratio of speeds of a motor boat to that of the current of water is 36:5. The motor along with the current in 5 hours 10 minutes.The time required to come back of motor boat is equal to

The speed of a motor-boat is that of the current of water as 36:5. The boat goes along with the current in 5 hours 10 minutes. It will come back in

(a) Suppose the windings og the armature in the d.c. motor or Example 4 connot tolerate a current of more than 20 amp. WhaT do you think will happen if the armature gets jammed and cannot rotate when the motor is connected to the supply ? (b) If the supply connection of the d.c. motor in Ex. are removed and the motor is used as a generated by connecting the shaft of its armature to an external mechanical rotor of speed 3000 r.p.m., how much e.m.f. will be generated ?

The armature of a shunt wound motor can with stand current up to 8 A before it overheats and it damaged. If the armature resistance is 0.5 Omega ,minimum back emf that must be motor is connected to a 120 V line is

A : When the frequency of the AC is increased, the displacement current increases. R : The sum of the conduction current and displacement current is constant.

A voltage V is applied to a dc electric motor. The armature winding resistance is equal to R . At what value of current flowing through the winding resistance is equal to R . At what value of current flowing through the winding will the useful power of the motor be the highest ? What is it equal to? What is the motor efficiency in this case ?