# Lenz’s Law and the Right Hand Rule

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## Introduction: Lenz’s Law and the Right Hand Rule

The modern world wouldn’t exist today without electromagnets; almost everything we use today runs on electromagnets in one way or another. The hard drive memory in your computer, the speaker in your radio, the starter in your car, all use electromagnets to work.

To understand how transformers, Tesla coils, electric motors, and a myriad of electronic devices work; you need to understand how electromagnets work and the Right Hand Rule.

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## Step 1: Current in a Conductor

Yes I said current not voltage; voltage is a potential across a conductor, and current passes through a conductor.

Think of voltage and current like water in a pipe and the pipe is your load. Water goes in the pipe at 35 psi at a rate of 5 gallons a minute. At the other end of the pipe water comes out of the pipe at 0 psi at a rate of 5 gallons a minute.

Like the water in the pipe current goes in the conductor and the same current comes out of the conductor.

## Step 2: The Right Hand Rule in a Conductor

When a current, (Red Arrow) is applied to a conductor it creates a magnetic field around the conductor. (Blue Arrows) To predict the direction of the of the magnetic fields flow around the conductor, use the right hand rule. Place your hand on the conductor with your thumb pointing in the direction of the current and your fingers will point in the direction of the magnetic fields flow.

## Step 3: The Right Hand Rule in a Coil

When you wrap the conductor around a ferrous metal like steel or iron, the magnetic fields of the coiled conductor merge and align, this is called an electromagnet. The magnetic field travels from the center of the coil passes out one end of the electromagnet around the outside of the coil and in the opposite end back to the center of the coil.

Magnets have a north and a south pole, to predict which end is North or South pole in a coil, again you use the right hand rule. Only this time with your right hand on the coil, point your fingers in the direction of the current flow in the coiled conductor. (Red Arrows) With your right thumb pointing strait along the coil, it should point to the north end of the magnet.

## Step 4: Solenoid Relays and Valves

Solenoids and relays are electromagnets that don’t rely on the right hand rule as much as other devices. However predicting north is easy on a single coil. Acting as switches and valves they are a simple device that only needs to move an actuator that opens and closes a switch or valve.

The actuator is spring loaded with the actuator out or away from the coils core. When you apply a current to the coil it creates an electromagnetic pulling the actuator towards the core of the coil opening or closing switches or valves.

## Step 5: How Transformers Work

Transformers are very dependent on the right hand rule. How a fluctuating current in a primary coil creates a current in a secondary coil wirelessley is called Lenz’s law.

All coils in a transformer should be wound in the same direction.

A coil will resist a change in a magnetic field, so when AC or a pulsing current is applied to the primary coil, it creates a fluctuating magnetic field in the primary coil.

When the fluctuating magnetic field reaches the secondary coil it creates an opposing magnetic field and an opposing current in the secondary coil.

You can use the right hand rule on the primary coil and the secondary to predict the output of the secondary Depending on the number of turns on the primary coil, and the number of turns on the secondary coil, the voltage changes to a higher or lower voltage.

If you find the positive and negative hard to follow on the secondary coil; think of the secondary coil as a power source or a battery where power comes out, and think of the primary as a load where power is consumed.

## Step 6: DC Electric Motors

The right hand rule is very important in motors if you want them to work the way you want them too. DC motors use rotating magnetic fields to rotate the armature of the motor. Brushless DC motors have a permanent magnet in the armature. This DC motor has the permanent magnet in the stator so the magnetic field in the stator is fixed and the rotating magnetic field is in the armature.

The brushes supply current to the segments of the commutator on the armature. The two act as a switch rotating the current from one coil winding on the armature to the next coil winding on the spinning armature.

The segments on the commutator supplies current to the armature winding’s making North and South just off to one side of the North and South of the starors permanent magnets. When South is pulled towards North the armature rotates to the next segment on the commutator and the next coil on the armature is energized.

To reverse the direction of this motor switch the polarity if the leads to the brushes.

## Step 7: AC DC Motors

AC DC motors use rotating magnetic fields in the armature just like DC motors use rotating magnetic fields to rotate the armature of the motor. Unlike DC motors, AC DC motors do not have permanent magnets in the stator or the armature. AC DC motors have electromagnets in the stator so the magnetic field in the stator is fixed when supplied with DC current. When supplied with AC current the magnetic fields in the armature and stator fluctuate in unison with the AC current. This makes the motor work the same whether it is supplied with DC or AC current.

The current first goes into the first stator coil energizing the first stator’s pole. From the first coil the current goes to the first brush supply current to the segments on the commutator on the armature. The brushes and the segments on the commutator act as a switch rotating the current from one coil winding on the armature to the next coil winding on the spinning armature. Last the current exits the armature via the the second brush and goes into the second stator’s coil energizing the second stators pole.

The segments on the commutator supplies current to the armature winding’s making North and South just off to one side of the North and South of the staror’s electromagnets. When South is pulled towards North the armature rotates to the next segment on the commutator and the next coil on the armature is energized.

Just like the DC motor; to reverse the direction of this motor swap the leads to the brushes.

## Step 8: Other Devices

There are just too many devices that use electromagnets to cover them all, the one thing you need to remember to work with them is Lenz’s Law and The Right Hand Rule.

Speakers work the same way a solenoid works the differences is the actuator is a permanent magnet and the coil is on the movable diaphragm.

Induction motors use rotating magnetic fields and Lens law to create the torque in the armature.

All electric motors use rotating magnetic fields and to predict the poles you use the right hand rule.

This is an entry in the
Magnets Challenge

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