DC Motor DC Generator DC Machines Lab 2

DC Motor & DC Generator DC Machines Lab # 2 Arsalan A Rahim Abdur Rehman Kashif 1

Magnetic Field of Current The magnetic field lines around a long wire which carries an electric current form concentric circles around the wire. The direction of the magnetic field is perpendicular to the wire and is in the direction the fingers of your right hand would curl if you wrapped them around the wire with your thumb in the direction of the current. Arsalan A Rahim Abdur Rehman Kashif 2

DC Motor Arsalan A Rahim Abdur Rehman Kashif 3

Magnetic Interactions with Moving Charge Arsalan A Rahim Abdur Rehman Kashif 4

Magnetic Force on Moving Charge Arsalan A Rahim Abdur Rehman Kashif 5

Magnetic Force on a Current Arsalan A Rahim Abdur Rehman Kashif 6

Fleming’s Left Hand Rule Fleming's left hand rule (for electric motors) shows the direction of the thrust on a conductor carrying a current in a magnetic field. Arsalan A Rahim Abdur Rehman Kashif 7

Magnetic Force The characteristics of this equation are as follows 1. The force is perpendicular to both the velocity v of the charge q and the magnetic field B. 2. The magnitude of the force is F = qv. B sinθ where θ is the angle < 180 degrees between the velocity and the magnetic field. This implies that the magnetic force on a stationary charge or a charge moving parallel to the magnetic field is zero. 3. The direction of the force is given by the right hand rule. The force relationship above is in the form of a vector product. Arsalan A Rahim Abdur Rehman Kashif 8

Units of Magnetic Field, B From the force relationship above it can be deduced that the units of magnetic field are Newton seconds /(Coulomb meter) or Newton per Ampere meter. This unit is named the Tesla. It is a large unit, and the smaller unit Gauss is used for small fields like the Earth's magnetic field. 1 Tesla = 10, 000 Gauss The Earth's magnetic field is of the order of half a Gauss Arsalan A Rahim Abdur Rehman Kashif 9

Lorentz Force Law The electric force is straightforward, being in the direction of the electric field if the charge q is positive, The direction of the magnetic part of the force is given by the right hand rule. Arsalan A Rahim Abdur Rehman Kashif 10

Magnetic Field in DC Motor Arsalan A Rahim Abdur Rehman Kashif 11

Current in DC Motor Arsalan A Rahim Abdur Rehman Kashif 12

Motor Working Arsalan A Rahim Abdur Rehman Kashif 13

Force in DC Motor Arsalan A Rahim Abdur Rehman Kashif 14

DC Motor Operation Arsalan A Rahim Abdur Rehman Kashif 15

Commutator and Brushes on DC Motor To keep the torque on a DC motor from reversing every time the coil moves through the plane perpendicular to the magnetic field, a split-ring device called a commutator is used to reverse the current at that point. The electrical contacts to the rotating ring are called “carbon brushes" Arsalan A Rahim Abdur Rehman Kashif 16

DC Generator work on the same principle as that of the DC Motor but in the reverse direction, i. e. the prime mover is attached to the Shaft, thus the voltage generated is available at the commutator. Fleming’s Right Hand Rule is used to find out the direction of the current in the moving conductor placed in a magnetic field Arsalan A Rahim Abdur Rehman Kashif 17

Fleming's Right Hand Rule Fleming's right hand rule (for generators) shows the direction of induced current flow when a conductor moves in a magnetic field. Arsalan A Rahim Abdur Rehman Kashif 18

Voltage Generated in a Moving Wire Arsalan A Rahim Abdur Rehman Kashif 19