Programming

  Magnetic Effect of Electric Current

Any substance that attracts iron and iron like objects is defined as magnet. When a wire carries

an electric current, it behaves as a magnet.

Properties of Magnet

Every magnet has north and south poles.
Same poles repel each other and unlike poles attract each other.A freely suspended magnet will align itself in north south direction, north facing north of the magnet and south facing south of the magnet.

Characteristics of Field Lines

Field lines arise from north pole and end into south pole of the magnet.They are closed curves.

Field lines never intersect each other.Direction of magnetic field lines inside the magnet is from south to north.

Properties of Magnetic Field Lines

Magnetic field lines originate from North Pole and end at South Pole.Magnetic field lines come closer to one another near the poles of magnet but widely separated at other places.

Magnetic field lines do not intersect each other.
Note: Magnetic field lines never intersect each other because resultant force at North Pole can only be in one direction. Had the lines intersected, it would be in two directions which not possible.Magnetic field produced by straight conductor straight conductor

Characteristics:

(a) Magnetic lines are concentric circles.
(b) The direction of magnetic lines reverses as we reverse the direction of the current.When current flows upward, the direction of magnetic lines is anticlockwise.When current flows downward, the direction of magnetic lines is clockwise.
(c) The Magnetic field produced is directly proportional to the current & inversely proportional to the distance from the conductor.
(d) To know the direction of magnetic field around a straight conductor, we have different sets of rules as given below:Fleming right hand rulerule👉
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Hold the forefinger, middle finger and thumb of right hand at right angles to each other. Forefinger points towards the direction of magnetic field, thumb points in the direction of motion of conductor and middle finger shows direction of induced current.

Solenoid

A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid.

Magnetic Effect of Current carrying Solenoid

A current carrying solenoid produces similar pattern of magnetic field as a bar magnet. One end of solenoid behaves as the north pole and another end behaves as the south pole. Magnetic field lines are parallel inside the solenoid; like a bar magnet; which shows that magnetic field is same at all points inside the solenoid

Electric Motor

Electric motor is a device that converts electrical energy to mechanical energy.



Parts of a Electric Motor

Insulated Copper wire: A rectangular coil of wire ABCD

Magnet Poles: A magnet as placed above ie North Pole and South Pole. This creates a magnetic field as shown above.

Split Rings: Two disjoint C-shaped rings P and Q. It acts as a commutator (which can reverse the direction of current)

Axle: The split rings are placed on the axle which can rotate freely.

Brushes: The outside of the split rings are connected to conducting brushes X and Y.

Source Battery: To source current.

Working

When the current begins to flow, current flows through brush X, then A to B, B to C, C to D and then to brush Y and into the battery.

Now applying Fleming's Left Hand Rule to wire AB, Current is along AB, Magnetic Field is as shown (North-> South), the motion of the wire is downwards.Now applying Fleming's Left Hand Rule to wire CD, Current is along CD, Magnetic Field is as shown (North-> South), the motion of the wire is upwards.The rectangular coil begins to move in the anti-clockwise direction

Note that during anti-clockwise motion, the split rings and axle also move, whereas the brushes don't move.

After half a rotation, Wire CD and Split ring Q moves to the left.  Wire AB and Split ring P moves to right. Brushes X and Y donot move.

Now applying Fleming's Left Hand Rule to wire CD, Current is along DC. (Battery -> Split ring Q -> DC , Magnetic Field is as shown (North-> South), the motion of the wire is downwards.

Now applying Fleming's Left Hand Rule to wire AB, Current is along BA. (Battery -> Split ring Q -> DC --> CB -> BA --> Split ring P) , Magnetic Field is as shown (North-> South), the motion of the wire is upwards.

So, again the coil rotates in the anti-clockwise direction.The reversal of current in the coil results in the continous rotation of the coil. The reversal of current is achieved by the commutator rings

Applications

Electric Fans

Refrigerators

Mixers

Washing machines