Magnetic Field Patterns
Current creates field: When electric current starts to flow through a conductor, like a wire, it automatically creates a magnetic field around it. This magnetic field is invisible but can affect magnetic materials and other currents nearby.
Circular pattern: Around a straight current-carrying wire, the magnetic field forms circles that go around the wire. These circular lines are closest and strongest near the wire and become weaker as you move away.
Right-hand grip rule: To find the direction of the magnetic field, you can use the right-hand rule. Point your right thumb in the direction the current flows, and your curled fingers will show the circular direction of the magnetic field lines around the wire.
Coil’s field: When the wire is shaped into a coil or solenoid and carries current, the magnetic field becomes more focused and resembles the field made by a bar magnet, with a clear north and south pole.
Force on a Current-Carrying Conductor
Force in magnetic field: If you place a wire that carries current into an external magnetic field, the wire will feel a force that pushes it sideways. This happens because of the interaction between the two magnetic fields.
Field interaction: The magnetic field created by the current in the wire combines with the external magnetic field, forming a new pattern of magnetic forces that interact.
Magnetic field names: This new pattern is often called magnetic flux or represented using magnetic field lines. These show the direction and strength of the field.
Fleming’s left-hand rule: To find the direction of the force on the wire, you can use Fleming’s left-hand rule: your thumb shows the direction of force, your first finger shows the magnetic field direction, and your second finger shows the direction of the current.
Lorentz force: The force that acts on the wire in the magnetic field is called the magnetic force or Lorentz force. It is responsible for the wire’s movement.
Factors Affecting Force Magnitude
Current strength: When the electric current flowing through the wire becomes stronger, the magnetic field it creates also becomes stronger. Because of this stronger magnetic field, the force acting on the wire increases, causing more noticeable movement in the wire within the magnetic field.
Magnetic field strength: If the magnetic field around the wire is made stronger—such as by using stronger magnets—the force that acts on the wire also becomes bigger. This is because stronger magnetic fields can interact more powerfully with the current in the wire.
Conductor length: The longer the part of the wire that sits inside the magnetic field, the more of it gets pushed by the magnetic force. So, a longer wire in the field will experience a stronger total force compared to a shorter one.
Orientation of conductor: The direction of the wire compared to the magnetic field also matters. The biggest force happens when the wire is placed at a right angle (90 degrees) to the magnetic field. If the wire is placed in the same direction as the magnetic field (parallel), then no force will act on it at all.
Effect of a Current-Carrying Coil
Coil forces: When a coil that carries an electric current is placed inside a magnetic field, the sides of the coil feel forces in opposite directions. One side of the coil is pushed upward while the other side is pushed downward. These opposite forces help the coil rotate.
Torque creation: These upward and downward forces on each side of the coil create a twisting action called torque. This torque makes the coil spin around its center, which is how movement is produced inside electric motors.
DC Motor
Function of DC motor: A DC motor is a machine that turns electrical energy into movement (mechanical energy). It uses the interaction between electricity and magnetism to make parts of the motor spin.
Coil in field: Inside the motor, there is a coil made of wire that carries current. This coil is placed between two magnetic poles, so it is always inside a magnetic field.
Role of magnets: Permanent magnets are placed around the coil to provide a constant magnetic field. This magnetic field interacts with the electric current in the coil and creates force to make it move.
Commutator purpose: The commutator is a special part shaped like a ring that is split in half. It switches the direction of the current flowing through the coil every half turn, which helps the coil keep spinning in one continuous direction instead of going back and forth.
Brushes’ role: The brushes are small blocks made of carbon. They stay in one place and press against the spinning commutator to keep the electrical connection between the power supply and the moving parts of the motor.
Continuous rotation: The coil keeps spinning because the commutator flips the direction of the current at just the right time. This keeps the magnetic force always pushing in a way that turns the coil in the same direction.
Factors Affecting Motor Speed
More current: When more electric current flows through the coil in the motor, it makes a stronger magnetic field. A stronger field means more torque is created, which makes the motor spin faster.
Stronger magnets: If the magnets used in the motor are stronger, they create a more powerful magnetic field. This stronger field increases the force on the coil, making it turn more quickly.
More coil turns: When the coil has more loops or turns of wire, the magnetic effects get stronger. This causes more force to act on the coil, helping it rotate faster and more efficiently.
Brushed and Brushless Motors
Brushed motor design: In a brushed motor, the electrical connection to the spinning coil is made using small carbon blocks called brushes. These brushes touch the rotating commutator to allow current to keep flowing into the motor.
Wear and sparks: Because the brushes rub against the spinning commutator, they cause friction. Over time, this wears down the brushes and can also cause small sparks to appear during operation.
Brushless motor design: In brushless motors, there are no physical brushes. Instead, electronic circuits are used to switch the direction of the current in the motor at the right time, which still allows the motor to spin.
Brushless motor benefits: Since brushless motors don’t have parts that rub against each other, they don’t wear out as quickly. They also make less noise, run more smoothly, and are more energy-efficient than brushed motors.