Unit 6a: Intro to Magnetism Magnetism and force between two charges are related—a result of the electromagnetic force 1. Magnetic field: region of space surrounding a magnet that exerts a force on other magnets and magnetic material a. Magnetic pole: regions of magnets that exert the strongest force i. North and South pole—opposite ends ii. Two north poles or two south poles repel each other (like repels like) iii. A north pole is attracted to a south pole of another magnet b. Field lines of magnet: the closer the lines are together, the stronger the magnetic field i. Field lines point from north pole to south pole. ii. The direction of the arrow indicates the direction the north pole of magnetized object would align in the field iii. Field lines go from north to south c. Earth’s magnetic field likely produced by spinning of iron and nickel core. i. Protects earth from solar winds which otherwise would strip the earth of the atmosphere ii. Aurora in polar regions caused when magnetosphere is disturbed and charged solar particles interact with atmosphere iii. Earth’s geographic North pole is the magnetic south pole.—north pole of magnet points toward north iv. Earth’s geographic South pole is the magnetic north pole— south pole of magnet points south v. The magnetic poles move and reverse orientation about twice every 1 million years 2. Materials that can become magnetized are called ferromagnetic a. Due to unpaired spin of electrons. (electrons usually are paired and have opposite spins) b. Include metals iron, nickel, cobalt c. Non-ferromagnetic materials-like aluminum-cannot interact with magnets d. Ferromagnetic materials have regions, called domains, with magnetically aligned atoms with north and south poles e. If the different domains are oriented randomly, they cancel out and there is no magnetic field f. If the domains are mostly aligned, a material becomes magnetic 3. Magnetizing ferromagnetic material a. When unmagnetized material becomes magnetized—domains reorient to become aligned b. Often, once moved away from the magnet, the domains return to random orientation and object loses magnetic properties c. If domains remain aligned for any length of time once removed from close magnetic field, the object is described as a permanent magnet d. Despite their name, permanent magnets can lose magnetic field over time (slow reorientation of domains through motion and vibrations in atoms) e. Heating a permanent magnet will quicken the process of becoming unmagnetized 4. A moving electric charge (current) is surrounded by a magnetic field. a. Right hand rule: if your extended right thumb represents direction of current, closed fingers represent field lines of magnetic field. b. Direction of current influences direction of magnetic field lines. 5. Electromagnet—temporary magnet created when there is current in a wire a. Solenoid--A single insulated wire wrapped into a cylindrical coil. b. A solenoid wrapped around an iron core (like a nail) increases the strength of the magnetic field 1000 X or more c. The more loops in a solenoid, the stronger the magnetic field. 6. Electromagnets used in electric motors (electrical energymechanical energy) a. The south pole of an electromagnet can move/rotate toward the north pole of a fixed permanent magnet b. When the electromagnet reorients itself in the field of the permanent magnet, the current of the electromagnet can be reversed c. The inertia of the rotating electromagnet keeps it moving, and the reversed attraction due to the reversed current allows a revolution of electromagnet d. Direct current can be used to power a motor using brushes, which conduct by gently touching a conductive commutator (ring-shaped conductor around the axis of rotation) e. The commutator is split so that the brushes briefly do not touch. When this happens, current does not flow. f. If the current was not disrupted, the electromagnet is continually attracted to the permanent magnet in one orientation and gets stuck 7. Electromagnetic Induction a. The generation of an electric current by a changing magnetic field b. Opposite idea of an electromagnet c. Generators (mechanical energyelectrical energy) i. Reverse principle of electric motor ii. A solenoid is rotated in a magnetic field, inducing current iii. Every 180° turn (half of a revolution), current reverses direction iv. Creates alternating current v. In US, generators turn 60 times a second (60 Hz), so that current alternates at 120 Hz 8. Motors and Generators can also work with fixed electromagnets and rotating permanent magnets 9. Transformers a. Device used to increase (step-up) or decrease (step-down) voltage b. 100,000 V from power lines needs to be stepped down to household 120 V AC c. 120 V AC often stepped down for electronic devices d. Transformers are in AC adaptors for cell phones and in many other devices 10. How transformers work a. Input voltage moves current through primary coil wrapped around one side of an iron core b. Output wire wrapped around other side of iron core c. Current from primary coil induces magnetic field in core d. Magnetic flux in core induces current in secondary coil e. If secondary coil has more turns in solenoid, output voltage goes up f. If secondary coil has fewer turns, output voltage goes down g. Ratio of output voltage to input voltage is equal to ratio of secondary coil turns to primary coil turns i. 𝑉𝑜𝑢𝑡 𝑉𝑖𝑛 = 𝑁2 𝑁1 I Vin = IoutVout ii. In an ideal transformer, input power equals output power (Pin = Pout), so in
© Copyright 2026 Paperzz