A DC motor converts electrical energy into mechanical energy. It works on the principle that when a current carrying wire is placed in a magnetic field, it experiences a mechanical force. Construction: A simple DC motor consists of magnets, a loop, a split ring, and brushes. The magnets inside the motor generate a magnetic field. A loop is kept within the magnetic field. The two ends of the loop are connected to the two halves of the split ring. These halves touch two conducting stationary brushes. It is through these brushes that the external circuit is connected. Working: When the current passes through the loop, its arms experience a mechanical force and hence the loop starts rotating. The more the current passing through the loop or the magnetic field strength, the more is the rotational speed of the loop. The direction of rotation of the loop can be reversed by changing the polarity of the magnetic field or by reversing the current through the loop. The left hand rule is used to find the direction of rotation of the loop of an electric motor, provided the directions of magnetic field and current are known. According to this rule, the first finger, second finger, and the thumb of the left hand are held in such a manner, that they are mutually perpendicular. Then, if the first and the middle finger point in the directions of field and current respectively, the direction of the erect thumb gives the direction of force on the arm. Objectives To know different parts of a DC motor To determine the direction of force acting on the arms of the loop using Fleming's left hand rule In this 3D simulation of a DC motor, you are given two parameters: current passing through the loop and strength of the magnetic field. Set their values using the respective sliders and observe the corresponding effect on the rotational speed of the loop. Check the effect of changing the polarity of the magnetic field and reversing the current within the loop. Determine the direction of force at both the arms (perpendicular to magnetic field) by clicking on 'Left Hand Rule'. Select the arm first. Then using the sliders orient the first and second finger of the left hand correctly to find the direction of force on the arm. Click on 'Check' to check whether you have applied the left hand rule correctly. Find the direction of force on the other arm in the same way. Click on ‘Show labels’ to know different parts of a simple DC motor. Change the values of current and magnetic field using the respective sliders and observe the change in rotational speed of the loop. Change the polarity of magnetic field and reverse the current in the loop by clicking on the respective button. Observe the change in motion. Select the arm first. Use the sliders to orient the first and second finger of the left hand correctly and then click on ‘Check’. Well done. You have applied the left hand rule correctly. Now select the other arm and find the direction of force on it in the same way. Oops! You made a mistake. Try again.Oops！ Conclusions The rotational speed of a loop in DC motor increases with increase in current and magnetic field strength. The direction of rotation of the loop reverses either by changing the polarity of magnetic field or by reversing the current within the loop. At every half rotation, the current in the loop gets reversed, and hence the direction of force also. Therefore, the loop continues to rotate in the same direction. S37700134_202 Fundamentals of DC Motor, motor, A.C. current, alternate current, mechanical work, direct current motor, current, magnetic field, conductor, mechanical force, Lorentz force, Fleming's left hand rule, stator, armature, rotor, shaft, field magnets, split rings, commutator, direct current, torque on a current loop, current carrying coil in a magnetic field, inertia of motion, maximum torque position
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