# Conventional current: the charges flow from positive to negative electron flow: the charges move from negative to positive the “flow of electrons” Hand.

## Presentation on theme: "Conventional current: the charges flow from positive to negative electron flow: the charges move from negative to positive the “flow of electrons” Hand."— Presentation transcript:

conventional current: the charges flow from positive to negative electron flow: the charges move from negative to positive the “flow of electrons” Hand rules: we will use our right hand when we are using conventional current and we will use our left hand when we use electron flow. We draw a force that goes into the page as an x. We draw a force that comes out of the page as a ○.

First Hand Rule We can find the direction of the magnetic field around a wire for a given current. Imagine holding a length of insulated wire with your right hand. Keep your thumb pointed in the direction of the conventional current. The fingers of your hand circle the wire and point in the direction of the magnetic field.

If we used the left hand rule, our thumb would be directed against the conventional current but our fingers would still point in the direction of the magnetic field.

Second Hand Rule A current in a solenoid creates a magnetic field with the field from each coil adding to the others. The solenoid has a north and a south pole and it is in itself a magnet. We can determine the direction of the magnetic field produced by an electromagnet if we know the direction of the current. Imagine holding an insulated coil with your right hand. If you then curl your fingers around the loops in the direction of the conventional current, your thumb will point toward the north pole of the electromagnet. If we used the left hand rule, our thumb would be directed against the conventional current.

1.If a current carrying wire is bent into a loop, why is the magnetic field inside the loop stronger than the magnetic field outside? 2.Suppose you are lost in the woods but have a compass with you. Unfortunately the red paint marking the north pole of the compass needle has worn off. You have a flashlight with a battery and a length of wire. How could you identify the north pole of the compass?

Third Hand Rule We can figure out the direction of the magnetic force when the current and magnetic field are known. Point the fingers of your right hand in the direction of the magnetic field and point your thumb in the direction of the conventional current in the wire. The palm of your hand will be facing in the direction of the force acting on the wire. If you use your left hand you will point your thumb against the conventional current.

If we have two wires next to each other and their currents are in the same direction they will be attracted to each other. If their currents are in opposite directions they will repel each other.

The force on a current-carrying wire in a magnetic field is equal to the product of the current, the length of the wire, and the magnetic field strength. F=BIL where F is the magnetic force (Newtons), I = current (amps), L = length (m), and B is the magnetic field strength (Tesla) - 1 Tesla = 1 N/A*m - If the wire is not perpendicular the equation becomes F =BIL*sin θ. If the wire becomes parallel to the magnetic field sin θ becomes zero and there is no magnetic force.

Example: A wire that is 0.50 m long and carrying a current of 8.0A is at right angles to a 0.40-Tesla magnetic field. How strong is the force that acts on the wire? Example: How much current will be required to produce a force of 0.38N on a 10.0cm length of wire at right angles to a 0.49-Tesla field?

Fourth Hand Rule We can use the fourth hand rule to find the direction of the forces on the charged in a conductor that is moving in the magnetic field. To generate current, either the conductor can move through a magnetic field or a magnetic field can move past the conductor. It is the relative motion between the wire and the magnetic field that produces the current. This process is called electromagnetic induction.

To find the force on the charged in the wire hold your right hand so that your thumb points in the direction in which the wire is moving and your fingers point in the direction of the magnetic field. The palm of your hand will point in the direction of the conventional current. This is how an electrical generator works. It converts mechanical energy to electrical energy. An electrical generator consists of a number of wire loops placed in a strong magnetic field. The wire is wound around an iron core to increase the strength of the magnetic field. The wire loops rotate through the magnetic field.

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