Introduction
There are many resemblances that can be observed in magnetic and electric phenomena. A magnet comprised of north and south poles which are opposite to each other. The opposite poles attract and likewise repel each other. A magnet has principle property to influence the surrounding space. This surrounding effect of a magnet is known as a magnetic field.
Magnetic fields consist of lines of force and force of attraction and repulsion that travel/or move along the lines. The developed forces depend on strength and distance apart the poles.
Figure 1: Magnetic lines of force for bar magnet
A magnet bar is rectangular shaped having properties of the magnetic field. It is made of steel containing ferromagnetic substance. It holds the properties of the magnetic field for sufficient long period.
Figure 2: Bar Magnet with magnetic field
In SI, the unit for strength of the magnetic field and magnetic flux density is called Tesla and it is derived unit and denoted by "T" or “B”. It is named by its inventor Nikola Tesla who defined it in the year 1960 as “ one Tesla is equal to one weber/ m2”
- Magnetic Bar
- Thick paper
- Steel Needles/or filings
Method
The following steps were performed in the procedure:
- Placed thick plain paper on a table,
- Placed the magnetic bar on surface having steel/or iron filling above the paper.
- Spread fine steel needle /or iron filings on the paper,
- Tapped the paper lightly and wrote the detailed observations around the magnet,
- Marked the dots by moving compass around the bar and draw the lines by joining dots located by the compass along the magnetic field lines,
- Sketched the circular outline of the field lines.
Results
Figure 3: Magnetic lines of force of a bar magnet
Conclusion
In conclusion, the properties of the magnetic lines of forces are as:
1. It originated from the North and ends at the South Pole.
2. They never intersect with each other.
3. Direction of line at particular point can be obtained by drawing a tangent at particular point.
4. They are remain continuous as originate from the north and ends at south Pole.
5. No line of force within the magnet.
Applications
- Mass Spectrometer
It is used is mass spectrometer which involves three steps including acceleration of ions with particular velocity, achieving required velocity followed by separation based on mass. All three stages are in accordance with principle learned by this course
- Hall Effect
The Hall Effect elaborates the force exerted by the moving charge and consequently it guide us to determine current in the wires by makeup –Ve charge. It facilitated and showed that charge flowing is the wire is positive or negative and provide uniform magnetic field.
Precautions
Make sure to clear all surfaces before beginning experiments and read the instructional manual carefully before starting the experiment. Use the needle with great care for accuracy and safety. In context of safety that is of prime importance in engineering, locate exits, fire blanket and extinguisher, gas and electricity shut-offs, first-aid kit, eyewash, and so forth. Keep the workplace neat and clean as well as dry.
Motors simply convert electrical energy into mechanical energy generated by battery or voltage source. The basic phenomena of motor are that when a wire having current is placed in the zone of the magnetic field, the force exerted on the wire.
When DC motor/or machine produces a continuous torque, it is compulsory that one of the windings should provide switching current. This switching current develops a moving flux field .In addition, typical DC motors consist of stator-mounted field winding that produces a flux in stationary space. The winding of the armature is located on the rotor. The armature coils are ended with copper bars that constitute parts of a commutator. The armature current is supplied to the commutator by creating a set of graphite brushes that drive on the surface of the commutator. When the rotor rotates, the consecutive commutator parts enter and leave the brush contact zone of brush.
Objective:
The objective of this experiment is to construct a DC motor by creating a magnetic field and to evaluate the basic principle of DC motors
Parts of DC Motor
- Field Winding 2. Pole Core
- Pole Shoe 4. Mean Magnetic Flux Path
- Field Pole 6.Laminated Armature Core
- Air Gap 8.Armature Winding Located In Slots
- Stator Frame 10.Brushes
- Pedestal 12.Commutator
- Rotor shaft 14.Armature core
Figure 1 Typical schematic diagram of a DC Motor.
Figure 2: Cross-sectional view of a DC
The magnitude of the force determines the speed of rotation and depends on:
- Magnitude of current in the wire
- Length of the wire to be used
- Strength of the magnetic field
Force = current x length x magnetic field
On the other hand, direction of spin depends on:
- Direction of the current in the wire
- Direction of the magnetic field
Left Hand Rule
Left-hand rule for motors is a pair of visual formulation developed by Fleming. Left hand rule s demonstrates working phenomena in a simple way to measure the direction of motion or electric current. Left hand rule phenomena is presented in figure below.
The directions keep the following conditions:
- Direction of magnetic field remain from north to south
- Direction of current flow is +ve to –Ve.
During application of left hand rule, we assume that charge move like a conventional current, i.e. +ve to –ve and velocity of charge must be in opposite in opposite direction
Figure 3-a: Representation of current and force by Left Hand Rule
Figure 3b: Representation of current and force by Left Hand Rule
Magnetic Ceramics
Magnetic ceramics is a material that holds a specific permanent magnetization that is called ferrimagnetism.
The main applications of ferrimagnetism areas:
- Used in transformer
- Used in telecommunications devices
- For recording information
Magnetic ceramics is manufactured by ferrites that are minerals in crystalline shape and combination of oxides of iron with other metals. The minerals are composed of iron oxide in combination with some other metal. The chemical formula for magnetic ceramics is M (FexOy)
M=Metal other than Iron
They are generally known as loadstones and chemical formula is Ferrous Ferrite [(Fe(Fe2O4)], or [Fe3O4] The magnetic properties of magnetite have been subjugated in compasses In ferromagnetism contains unpaired electron and spinning of electrons remains in one direction within a specified domain,
- Magnetic Bar
- Supporting Hangers
- Battery
- Copper enamel coil
- Leads
- Wood Base
- Thumbtack
Method
The following steps are performed in this experiment:
- Placed the wire around a small cylinder for making loops. This loops of coils is called the rotor. Left some wire on each side of the rotor,
- Held the loop vertically by placing thumb in the center of the rotor ,
- Striped the wire from the coil,
- Striped other straight section of wire including sides, top and bottom,
- Prepared to assembly for the motor as shown in figure in result section,
- Placed the ceramic magnet in the center,
- Placed the rotor on the supports and adjusted the magnet and/or supports in accordance,
- Completed the circuit and touched red wire from the battery
Results
Figure 4: Experimental set up for construction of DC motor
Conclusion
The performed experiment provided the result in accordance with basic principle of DC Motors which simply convert electrical energy into mechanical energy generated by battery by rotating rotor in developed magnetic field. This also proved the basic phenomena of motor that when a wire having current is placed in the zone of the magnetic field, the force exerted on the wire and rotor start moving under this developed magnetic field.
The performance can be improved by using suitably built supporting hangers to keep the balance. Number of loops of enamel copper coil can be increased to get higher power and speed. In future, moisture content should be taken into consideration as it may effect rotation and speed due open assembly framework of experiment
Precautions
The assembly should be in balanced position to avoid frictional forces. The motor should be turned off by disconnecting leads. In addition, make sure to clear all surfaces before beginning of experiments and read the instructional manual carefully before starting the experiment. Use the assembly with great care for accuracy and safety. In context of safety, it is of prime importance in engineering, to locate exits, fire blanket and extinguisher, gas and electricity shut-offs, first-aid kit, eyewash, and so forth. Keep the workplace neat and clean as well as dry.
