Untitled Quiz

Electromagnetic Effects

• A magnetic field is created when an electric current flows through a wire.
• Direct current (DC) produces a constant magnetic field.
• Alternating current (AC) produces an alternating magnetic field.
• The magnetic field around a current-carrying wire is circular and perpendicular to the wire.
• The strength of the field weakens with distance from the wire.
• The corkscrew rule can be used to determine the direction of the magnetic field.

Study Skills

• To determine the magnetic field direction, use the corkscrew rule.
• In the rule, align your right hand with the wire, thumb in the direction of the current flow, and your curled fingers will point in the direction of the magnetic field.

Extended

• A compass placed around a wire will align with the magnetic field's direction.
• Force on a compass needle is proportional to the magnetic field at the compass point.
• A solenoid (a coil of wire) produces a magnetic field similar to a bar magnet.
• The magnetic field strength in a solenoid is greatest inside the coil.
• Increasing the current or the number of turns in a solenoid increases its magnetic field strength.

Applications of Electromagnets

• Electromagnets are extremely useful devices with varied applications.
• They're strong, controllable, and easily switched on/off.
• Used in scrap metal cranes, door locks, starter motors, relays, and electric bells.

Force on a Current-Carrying Conductor

• A current-carrying wire in a magnetic field experiences a force.
• Increasing any of the following increases the force:
• current in the wire
• number of individual wires
• strength of the magnetic field
• length of the wire within the magnetic field
• The direction of the magnetic field or current alters the direction of the force.
• Fleming's left-hand rule is used to determine the force direction.
• Current (I), magnetic field (B), and the force (F) are mutually perpendicular.
• If the field and current are parallel, no force occurs.

Forces on Charged Particles

• Any moving charged particle in a magnetic field experiences a force.
• Conventional current flows from positive to negative.
• A negative charge moves in the opposite direction to current flow.
• Fleming's left-hand rule determines force direction for negative charges.

The DC Motor

• Electric motors are highly reliable with one moving part.
• A current-carrying wire experiences a force in a magnetic field.
• DC motors rely on this force for rotational motion.
• Clever designs enable various speeds without gears.

Electromagnetism Induction

• Induction is the process of generating/inducing an electromotive force (e.m.f.) from magnetism.
• An induced e.m.f. is created when a wire is within a changing magnetic field. This is called Faraday's Law.
• Move a magnet in/out of a coil to induce an electromotive force (e.m.f.)
• An electric current is generated.
• Changes in speed, coil type, reversing the magnet will affect the magnitude/sign of voltage/ current.
• Inducing e.m.f. can also occur with the magnet stationary while moving the associated coil of wire through it.
• The changing magnetic field causes a current to be induced in the wire which follows Lenz’s Law - the induced e.m.f. opposes the change that created it.

AC and DC Generators

• AC generators produce alternating current while DC generators produce direct current. Both use similar principles.
• Rotating coils within a magnetic field creates alternating electromotive forces (e.m.fs) in an AC Generator.
• A DC Generator uses a split-ring commutator (in place of slip rings) to change the direction of the current to flow consistently in one direction.
• Basic motor/generator mechanics are the same principle, with the difference being what initiates the spin and whether a change in direction of the e.m.f. is required.

Transformers

• Transformers increase or decrease alternating voltage.
• Step-up transformers increase voltage.
• Step-down transformers decrease voltage.
• Basic transformer design uses a primary and secondary coil wrapped around a soft iron core.
• Transformers only work with AC due to the need for a continuously changing magnetic field.
• Transformers must operate according to the equation: (Voltage in primary) / (Turns in primary) = (Voltage in secondary) / (Turns in secondary).
• Transformers obey conservation of energy (power in = power out)

Practical Applications

• Electricity transmission cables lose energy as heat when currents are high; high voltages reduce this heat loss.
• High-voltage transmission uses step-up transformers.
• Step-down transformers are used in homes to reduce voltage to a safe level. – Tesla coils utilize a step-up transformer to demonstrate high-voltage arcing effects.