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The Right-Hand Rule

  • Introduction
  • Results & Video
  • Materials
  • Procedure
  • Preparation & References
  • Downloads

eflowScientists need to have a convention (a common method) for describing the direction of electric currents (I) and magnetic fields (B). By convention the direction of electric current is described as running from the (+) electrode toward the (-) electrode. Interestingly, the flow of electrons, which create the current, is in the opposite direction. Electrons are negatively charged and flow toward the positive electrode.

 

The Right Hand Rule for Electric Current through a Wire (or Solenoid)

right-hand ruleMovement of any charged particles creates a magnetic field (B). For electricity, the charged particles are electrons, which are negatively charged. In this activity, the flow of current (I) through the wire creates a magnetic field that wraps around the wire. To establish the direction of the field, scientists use the Right Hand Rule.

In this activity, students apply the Right Hand Rule to predict the direction of a magnetic field around a current, and then verify their hypothesis using compasses, which are arranged around the wire. The direction of the current is then reversed and students observe the reversal of the direction of the magnetic field as the compasses arrows reverse direction.

 

Predicting the Direction of the Force generated by 2 Interacting Fields

The Right Hand Rule is also applied to determine the direction of the vector product of any 2 vectors that are perpendicluar to each other. In this way, the direction of a resultant Force can be determined when an electric current moves through a static magnetic field.

vector

For this application of the Right Hand Rule, point your thumb in the direction of the electric current (I) and your index finger in the direction of the magnetic field (B). If you bend your middle finger (or use your palm) it will point in the direction of the Force (F) generated by the interaction of these 2 fields.

 

 

Video & Results

setup

The drawing to the right illustrates the expected results. The arrows in the circles represent the direction of north as indicated by the compasses. When the students disconnect the leads to the battery and then reconnect to the swapped electrodes, the arrows will reverse direction.

 

 

The arrointows pointing north on each compass will be tangent to a circle whose center is the wire. For this circle, we are looking from above the platform. Point your thumb into the screen or paper and wrap your fingers. The north direction on each compass, which is aligned with the local magnetic field (not Earth's) will be clockwise.

outIf the current is reversed, the north arrows on each compass will now point counter-clockwise. For this illustration, we are again looking from above the platform and the current is coming up toward us. Point your thumb up (out of the page or screen), and curl your fingers. They will wrap in a counter-clockwise direction.

 

 

 

The arrows will reverse when the current runs

Materials

  • 4 or 5 small compasses (orderd on Amazon, 12 compasses for $10)
  • platform (cardboard or posterboard to hold the compasses)
  • thick wire made from non-paramagnet metal (aluminum, stainless steel NOT iron)
  • electric leads with alligator clips
  • 6 volt lantern battery
  • non-metallic platform to support the wire. (some have used tinker toys)

Procedure

The Right Hand Rule

Here is how the rule works.right-hand rule

  1. Imagine that there is electric current (I) running vertically through a wire from the table upwards. Point the thumb of your right hand in the direction of the electric current.
  2. Now curl your fingers. Your fingers will wrap in counter-clockwise direction. Your fingers indicate the direction of the magnetic field (B) at points around the wire. (The field will be tangent to a circle with arrows pointing counter-clockwise.)
  3. Now point your thumb in the opposite direction and notice that your fingers wrap in the clockwise direction, indicating that if the electric current is reversed the magnetic field will be reversed as well.

Testing the Right Hand Rule

We now know that the arrows on a compass align in magnetic fields. For this exercise, the arrows pointing in the North direction on a compass will indicate the direction of the magnetic field at various points around the wire.

  1. Examine the setup for this exercise. On the battery identify the positive (+) and the negative (-) electrodes but do NOT connect the leads to it yet.
  2. Connect the alligator clips to the ends of the thick wire with one lead above the platform and one lead below the platform that is holding the compasses.
  3. Observe or draw the direction of the compass arrows. The arrows should be pointing to magnetic North and should be parallel to each other.
  4. Pick the electrodes to which you will connect the leads on the lantern battery. Before you connect them, use the Right Hand Rule to show the direction of the magnetic field.
  5. Observe the direction of the compass arrows. Did they rotate as you expected?
    NOTE: Do NOT leave the leads connected to the battery for long periods of time, it will drain the battery.
  6. Reverse the direction of the current by swapping the electrodes to which the leads are connected. What did the arrows on the compasses do?
Preparation & Notes
Download Files