Electricity & Magnetism Static Electricity Electricity & Magnetism

Static Electricity Matter is composed of small particles called atoms. The atom is composed of protons, neutrons, and electrons. Normally, atoms are neutral (no charge) because they have the same number of protons as electrons. Some substances can gain and lose electrons easily because of their properties.

Static Electricity When a balloon is rubbed with a wool cloth (friction), the wool cloth loses some of its electrons. Because the wool cloth now has more protons than electrons, it is positively charged. The balloon has gained electrons and is, therefore, negatively charged. By bringing the negatively charged balloon into contact with positively charged items, they become attracted.

Law of Electrostatics This is an example of one of the basic Laws of Electrostatics: Unlike charges attract each other. It also states that like charges repel. Example: If two negatively charged balloons are brought near each other, they repel each other.

Static Electricity Electrons sometimes jump between objects. When this happens we sometimes hear a “crack” and, in darkness, see a spark.

Producing Electric Energy Electricity & Magnetism

Magnets and Magnetism An electric current flows when electrons move from atom to atom through a conductor. In 1820, Hans Oerstead, a Danish physicist, discovered that electric current passing through a wire produces a magnetic field around the wire. If the wire is coiled around an iron ore an electromagnet is produced.

Producing Electric Energy Other methods of generating electric current have been found, such as with chemical energy. The wet cell, a battery, consists of a copper strip (positive electrode) and a zinc strip (negative electrode) in a diluted acid solution. The acid solution, known as an electrolyte, is capable of conducting an electrical current.

Producing Electric Energy Electrons leave the copper strip, giving it a positive charge. As the zinc dissolves, it has surplus electrons, giving it a negative charge. Electrons flow from the zinc strip through the conductor to the copper strip. The electrical current produced from the flow of electrons can cause a bulb to light.

Producing Electric Energy The current produced is called direct current (D.C.). Heat energy can also be used to generate an electrical current. When set of dissimilar metal strips (called thermopiles) are heated, an electric current is generated that flows through the connecting wires.

Producing Electric Energy An instrument called the ammeter measures electric current. Sunlight can also be used to produce electricity. Solar cells consist of semiconductors made of silicon crystals. The sun’s energy can cause electrons to flow between the semiconductors, producing a small current.

Producing Electric Energy A power plant generator consists of electromagnets that are made to spin within an armature, which consists of many coils of wire. The process begins with a turbine, which will turn from the force of wind, moving water, or heated water (steam).

Producing Electric Energy At the spinning of the turbine and shaft cause electromagnets to spin within the armature. This current is used to supply the electromagnets and to supply electrical energy for consumers. The current generated is called alternating current (A.C.)

Electricity & Magnetism Complete Circuits Electricity & Magnetism

Complete Circuits The electrical energy produced by a generator or battery can be made to follow certain paths. The flow of electrical energy is called an electrical current. The electrons flow in a metal conductor, such as copper wire, is from the negative to positive pole.

Complete Circuits The path taken by the electrical current is known as a circuit. When the pathway is unbroken and the current flows from the source through the conductor and back again, the circuit is said to be complete.

Complete Circuits When someone flips on a light switch, the circuit is complete and electrical current flows through the light bulb, producing light. When someone pushes a doorbell button the circuit is complete and the bell rings. The complete circuit is also called a closed circuit because there is no opening or break in the path of electron flow.

Complete Circuits A switch allows one to control the flow of electrical current. When the switch is open, or in the off position, the current cannot flow through the conductors. This is called an open circuit.

Complete Circuits If the electric current completes a circuit without servicing the device it was intended to operate, as when two bare conductor wires come in contact with each other, a “short circuit” results. This causes the wire to heat up without operating the electrical device.

Series and Parallel Circuits Electricity & Magnetism

Series and Parallel Circuits Electrical current can be measured in several ways. Electrons flow through a conductor when there is a surplus of electrons at one pole and a deficit at the other pole. The electrical potential of the two poles is different. This difference is known as the electromotive force (EMF), or voltage.

Series and Parallel Circuits The instrument used to measure voltage is the voltmeter. The rate of flow of the electrical current is measured in units called amperes (amps). The ammeter is the instrument used to measure amperage. As the electrons move through the conductor, a certain amount of opposition is known as resistance and is measured in units called ohms.

Series and Parallel Circuits Various factors affect the resistance of a conductor: Type of material Thickness of material Length of material

Series and Parallel Circuits A complete circuit can be set up in two ways, a series or parallel circuit. In the series circuit the electrons have only one path through which they may flow. When two bulbs are connected in series with one dry cell, the ammeter shows that the strength of the current is less when compared to a one bulb circuit because the second bulb acts as a resistor.

Series and Parallel Circuits When two bulbs are connected in parallel with one dry cell, the ammeter indicates greater amperage compared to the one bulb circuit. This is because the current has more than one path to follow so there is less resistance.

Electricity & Magnetism Magnets and Magnetism Electricity & Magnetism

Magnets and Magnetism Magnetic iron ore was discovered by the Greeks in a region once known as Magnesia. Natural magnets, called lodestones, are composed of the mineral magnetite. Certain materials such as iron (steel), nickel, and cobalt are attracted to magnets and can be formed into magnets of various shapes.

Magnets and Magnetism The domain theory of magnetism is based on the concept of the magnetic field of individual atoms. Certain elements, such as iron, can become aligned. The aligned clusters of atoms then form magnetic domains within pieces of iron.

Magnets and Magnetism The attraction or repulsion is strongest at the ends, called poles. One end is the north seeking pole (N) and the other is the south seeking pole (S). When like poles are brought together they repel each other, unlike poles attract each other.

Magnets and Magnetism The magnetic field in the space around a magnet is defined by the lines of force. The patterns of these invisible lines of force can be seen when iron filings are sprinkled around a magnet.

Magnets and Magnetism The earth behaves as a huge magnet and therefore has magnetic lines of force. It is these lines of force that align the north end of a directional compass needle to the magnetic north pole of the earth.

Electricity & Magnetism Electromagnets Electricity & Magnetism

Magnets and Magnetism In an unmagnetized piece of iron the domains are randomly oriented. However, if the piece of iron is placed next to a strong magnet, many of the domains will arrange themselves in line with the magnetic field.

Electromagnets Electromagnets have three requirements: Electric current Coiled, insulated wire A soft iron bar When a current flows through the coiled wire wrapped around the bar (core), the bar and coiled wire act like a magnet. They can pick up objects and they have north and south seeking poles.

Electromagnets For electromagnets, a soft iron bar is used because it magnetizes easily and also loses its magnetism easily. An electromagnet will continue to be a magnet as long as the current flows through the coiled wire. For this reason, electromagnets are called temporary magnets.

Electromagnets When a current flows through a wire, a magnetic field (lines of force) occurs. In an electromagnet the lines of force occur around the soft iron core and coiled wire. The electric force of an electromagnet can be made stronger in two ways: By increasing the number of turns of coiled wire around the core And/or by increasing the amount of electric current

Electromagnets Doubling the number of turns of wire or doubling the electric current will double the magnetic force of the electromagnet. The poles of the electromagnet can be reversed by reversing the wire connection at the source of electricity. Pole designation may be determined by using a compass.

Electromagnets Electromagnets are used in many objects: Telephones Telegraphs Radios Televisions Motors Doorbells Electrical appliances