Electromagnetism

Magnetic Force and Fields Every magnet has two poles: N-pole: the pole that seeks the northerly direction on Earth S-pole: the south-seeking pole

Law of magnetic poles: Opposite magnetic poles attract and similar magnetic poles repel Magnetic field of force: The space around a magnet in which magnetic forces are exerted. Represented by field lines – a compass needle would follow these lines if allowed to travel along them. 3-dimensional in nature for all magnets

Magnetic fields around Bar Magnets

In the magnetic field line displays of the parallel straight conductors shown below, indicate which shows repulsion and which shows attraction. Indicate also for both whether the currents in the wires (blue dots) are travelling in the same direction or opposite to each other. ATTRACTION REPULSION Currents travelling in SAME direction Currents travelling in OPPOSITE direction

Oersted’s Discovery Principle of Electromagnetism Whenever an electric current moves through a conductor, a magnetic field is created in the region around the conductor. Oersted discovered this accidentally when a compass needle placed just below a wire carrying a current took a position nearly perpendicular to the wire when the current was flowing.

The Magnetic Field of a Straight Conductor The magnetic field around a straight conductor consists of concentric circles around the conductor, with the conductor being at the centre of the circles. As the distance from the conductor increases, the field becomes weaker and the space between the lines becomes more spaced. There are no poles. The field lines are continuous.

Right-Hand Rule for a Conductor If the current in the conductor is reversed, the direction of the field lines would be reversed also. We use the Right-Hand Rule for a Conductor to remember the relationship between the direction of the field lines and the direction of the current.

If a straight conductor is held in the right hand with the thumb pointing in the direction of the current, the curled fingers point in the direction of the magnetic field lines. REMEMBER: The magnetic field around a conductor is 3-dimensional in nature!!!