Electricity and Magnetism

Four Fundamental Forces of Nature

1. Gravitational Force

2. Electromagnetic Force

3. Strong Nuclear Force

4. Weak Nuclear Force

Gravitational Force

Attraction between all objects with mass.

Electromagnetic Force

Force between charged particles (electricity and magnetism).

Strong Nuclear Force

Holds protons and neutrons together in an atom’s nucleus.

Weak Nuclear Force

Responsible for radioactive decay and certain nuclear reactions.

Magnetism

- Is a force

- Pulls and pushes objects by generating the so-called magnetic field.

Magnets

Have the ability to attract materials that are magnetic in nature.

Magnetic Poles

North Pole (N) and South Pole (S)

Magnetic Material

Is one which can be magnetized and is attracted to magnets.

Ferromagnets

- Iron (Fe), Cobalt (Co), Nickel (Ni)

- Materials that are described as hard magnetic or soft magnetic materials.

Hard Magnetic Materials

Are materials that are difficult to magnetize but retain their magnetism for a long time once magnetized.

Soft Magnetic Materials

Are materials that magnetize easily and lose their magnetism quickly when the external magnetic field is removed.

Steel

- A hard material

- Is difficult to magnetize; however, it does not readily lose its magnetism.

Iron

- A soft material

- Is relatively easy to magnetize, but its magnetism is only temporary.

Magnetic Levitation (MagLev)

A technology that uses magnetic forces to lift and propel objects (without touching the tracks).

Nonmagnetic Materials

1. Copper

2. Zinc

3. Aluminum

4. Tin

5. Brass

Properties of Magnets

1. Like poles repel and unlike poles attract each other.

2. When allowed to hang freely, magnets always align in one particular direction.

3. Magnetic poles always occur in pairs.

Magnetic Field

- Is a region in which a magnetic force can be detected.

- Can be investigated using a small compass and magnetizable materials like iron fillings.

Compass

- Consists of a tiny magnetic “needle” that spins around when placed near a magnet.

- Spinning stops when the north seeking pole and the south seeking pole of the needle become oriented toward the north pole and the south pole of the bar magnet, respectively.

Magnetic Flux

The number of magnetic field lines per area.

Tesla (T)

- In honor of the Serbian-American physicist Nikola Tesla (1857-1943).

- The SI unit of the magnetic field strength (B).

- One tesla is equal to one newton per ampere-meter, N/A • m.

- Its magnitude is equal to the number of flux lines per unit area of a magnetic field.

Weber (Wb)

- In honor of Wilhelm Weber (1804-1891).

- The SI unit of magnetic flux (Φ).

- One weber is equal to one tesla square meter. T • m².

- It measures the number of flux lines, where 1 Wb = 108 lines of flux.

Hans Christian Oersted

- A Danish physicist, chemist, and philosopher.

- Made an interesting observation in the year 1820, which started others looking into the relationship of electricity and magnetism.

- Concluded that the point of a compass needle would follow a magnet.

- His discovery paved the way for the invention of new gadgets using the principles of electro-magnetism.

Electromagnet

- A coil of wire carrying current that creates a magnetic field.

- When a soft iron core is placed inside, the magnetic strength increases.

→ The strength depends on:

1. Number of turns in the coil

2. Size of the iron core

3. Amount of current

Energy

The ability to move an object through a distance.

Electrical Energy

Energy associated with electric current.

Mechanical Energy

Energy due to motion or position.

Energy Transformation

When a current-carrying wire is placed in a magnetic field, and that is the conversion of electrical energy into mechanical energy.

Electric Motor

- Converts electrical energy into mechanical energy.

- Uses a current-carrying coil (armature) placed in a magnetic field.

→ Contains:

1. Electromagnet (Armature)

2. Permanent Magnet

3. Commutator

Electromagnet (Armature)

Rotates within the magnetic field.

Permanent Magnet

Provides the field.

Commutator

The part which reverses the flow of current through an electric motor.

Galvanometer

Are devices that measure electric current. In these devices, there is a response of magnetic forces between an electromagnet and a permanent magnet.

Galvanometer

Measures small amounts of electric current. The rotation of a loop of wire in a magnetic field is the basis for this device.

Ammeter

Is a galvanometer with parallel resistor and connected in series with the load to measure the current passing through it.

Voltmeter

Is a galvanometer with series resistor and connected in parallel with the load to measure the voltage across it.

Oersted’s discovery was put into mathematical form by three French physicists who extended his work

1. Jean-Baptiste Biot (1774-1862)

2. Felix Savart (1791-1841)

3. Andre-Marie Ampere (1775–1836)

Later, others explored if the process could be reversed — using magnetism to generate current.

1. Joseph Henry (USA)

2. Michael Faraday (UK)

3. Heinrich Lenz (Russia)

Faraday’s Law

The electromotive force (emf) induced in a loop of wire is proportional to the rate of change of magnetic flux through the coil and is present even if the circuit resistance is infinite and the current is zero.

Lenz’s Law

The direction of an understanding of induction of induced current is such that its own magnetic field opposes the original change in magnetic flux that induced the current.

Electromagnetic Induction

The process of inducing a current by moving a magnetic field through a wire coil.

Electric Generator

- Converts mechanical energy into electrical energy.

- A coil of wire (armature) rotates in a magnetic field, inducing current.

AC Generator (Alternator)

- Produces alternating current (AC) using slip rings.

- As the coil spins, current direction reverses every half turn.

- Has an armature, a permanent magnet, and slip rings.

DC Generator

- It is like an AC generator, except that it contains a commutator (a connector that reverses the connection from the loop to the outside circuit each half turn) instead of slip rings.

Commutator

A connector that reverses the connection from the loop to the outside circuit each half turn.

Transformer

- Make it possible to send power over long distances through power lines.

- Voltage and current in AC circuits can be increased or decreased using this device.

- Consist of a primary coil (connected to power source) and a secondary coil (connected to the output circuit) wound around a soft iron core.

→ Classified into two types:

1. Step-up transformers

2. Step-down transformers

Step-up Transformers

Increase the voltage and decrease the current.

Step-down Transformers

Reduce the voltage and increase the current.