# 0016: Electricity and Magnetism 1

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0016: Electricity and Magnetism 1
0016: Electricity and Magnetism 1. recognize the characteristics of static electricity

Electricity describes charged particles
Rub a balloon with wool, picks up electrons Rub glass with silk, loses electrons Objects attract or repel when “electrically charged” “static electricity”

Figure 5-1 The two kinds of electrical charges. Opposite charges attract, while like charges repel.

Electricity describes charged particles
These charged particles can be at rest (“static electricity”) or they may be moving (“current electricity”)

Coulomb’s Law The electric force between two charged particles varies directly as the product of their charges and inversely as the square of the separation distances. force (newtons) = k x 1st charge x 2nd charge / distance2

Electrical Field A kind of “aura” or “force field” around every electric charge Extends radially away from the proton and in opposite direction about the electron.

…distinguish between conductors and insulators
Material that electrons are able to pass through Metals, ionic solutions Insulators Material that electrons do not through easily Glass, wood, rubber, plastics

0016: Electricity and Magnetism 2
0016: Electricity and Magnetism 2. demonstrate knowledge of the components of an electric circuit and their functions.

Electrical potential and electric current
Movement of electric charge creates electric current Charges move as current only when energy is supplied to them Circuit Switch Voltage Current

If we use the water analogy…
Voltage = the pressure Current = the rate of flow

Voltage The push that makes electrons move.
1.5 V “D” cell or 6 V lantern battery Higher voltage = greater push on electrons Water analogy Voltage causes current.

Electric Current Voltage creates current
Current is the amount of charge passing a point in a circuit in a second Metric unit = Ampere (A) Measures by an ammeter Different devices often carry different amounts of current

…distinguish between DC and AC
Direct current Current moves in one direction From dry cells or batteries Alternating current Pumped to us by Cobb EMC Oscillates back and forth at 60 Hz wall sockets

Ohm’s Law How is current related to voltage?
Direct relation between the two led to discovery of “resistance” Voltage / Current = Resistance (V / I = R)

Resistance measures how hard it is for current to move through a conductor (unit = Ohm). Easier for electrons to move through thick wires than thin wires Light bulb filament, thin, high resistance, heats up and glows

0016: Electricity and Magnetism 3. compare series and parallel circuits.

…distinguish between Series Circuits & Parallel Circuits
Only one path for current flow Same amount of current thru entire circuit Cheap string of decorative lights Alternate paths for current flow Current divides up among the paths Wiring system for lights and elec outlets in homes & buildings

Electrical Safety Fuses Circuit breakers Ground-fault interrupter

Electric Power Power = energy used / time
Also calculated as product of current and voltage Watts = amp’s x volts Ex: 60W bulb draws .5 A on a 120V line 120W lamp draws 1A on a 120V line If a 120V line to a socket is limited (by a fuse) to 15A, will it operate a 1200W dryer?

0016: Electricity and Magnetism 4
0016: Electricity and Magnetism 4. identify properties of magnets and characteristics of magnetic fields.

Magnetism Children are fascinated by magnets! “floating” paper clip
“jumping” nails “iron filing” cartoon hair

The little fridge magnet reminds us that the magnetic force on Earth is stronger than gravity.

magnetism Magnesia, province of Greece
Unusual property of lodestone noted over 2000 years ago

12th C, Magnets first used in navigational compass, Chinese

16th C, William Gilbert “Every magnet has two poles, a north and a south.” “Like magnetic poles repel, unlike poles attract.”

Figure 5-3 A compass needle and the Earth. Any magnet will twist because of the forces between its poles and and those of the Earth. Every magnet has at least two poles.

Courtesy Andy Washnik Figure 5-5(b) Iron filings placed near a bar magnet align themselves along the field.

Figure 5-4 A magnetic field. Small magnets placed near a large one orient themselves along the lines of the magnetic field, as shown.

Figure 5-5(a) A bar magnet and its magnetic dipole field.

“Opposites attract. Likes repel.”
The above describes both magnetic and electric force, but electric charges can be isolated, magnetic poles cannot.

Figure 5-6 Cut magnets. If you break a dipole magnet in two, you get two smaller dipole magnets, not an isolated north or south pole.

0016: Electricity and Magnetism 5
0016: Electricity and Magnetism 5. demonstrate knowledge of the relationship between moving electric charges and magnetic fields and applications of electromagnets in everyday life (e.g., motors, generators)

1820, Hans Oersted …connected a battery to let electric current flow, and noticed a compass needle twitch and move.

Electricity & Magnetism: “ two sides of the same coin “
Every time an electric charge moves, a magnetic field is created. (electromagnet) Every time a magnetic field varies, an electric field is created. (hydroelectic dams)

Electric motors convert electricity into magnetic fields, for useful rotary motion

Figure 5-8 An electric motor. The simplest motors work by placing an electromagnet that can rotate between two permanent magnets. (a) When the current is turned on, the north and south poles of the electromagnet are attracted to the south and north poles of the permanent magnets. (b)–(d) As the electromagnet rotates, the current direction is switched, causing the electromagnet to continue rotating.

Electric motors convert electricity into magnetic fields, for useful rotary motion

Electrical Generators
…are the exact opposite of electric motors: they convert rotary motion into electrical energy. link

Energy Transformation - kinetic energy of moving water can be used to turn a wheel that runs the mill to grind grain.

Energy Transformation Wind can be used to vary a magnetic field about wires, to generate alternating current.

We can burn coal to heat water to produce steam to turn a turbine to vary a magnetic field about wires, to generate alternating current. (coal-fired power plant)

We can dam rivers, then release energy from the lake side, to turn a turbine, to vary a magnetic field about wires, to generate alternating current. (hydroelectric energy)

We control nuclear fission reactions to heat water to produce steam to turn a turbine to vary a magnetic field about wires, to generate alternating current. (nuclear energy)

In some parts of the world, we can use heat from the Earth to produce steam to turn a turbine to vary a magnetic field about wires, to generate alternating current. (geothermal energy)

Anything that can turn an axle can power a generator.
Flowing water, pressurized steam, wind, or a gasoline engine can drive a rotating turbine that houses coils of copper wire.