Electricity Chapter 17

Electric Charge & Static Electricity A buildup of static electricity can cause little “shocks” This is from an electric charge. Charges: Charged objects exert a force on other charged objects Two types of charges are positive and negative charges. Like charges repel & opposite charges attract.

Electric Force & Electric Field The force between charged objects is an electric force. Strength of force is determined by size of charges, and distance between the objects. The electric field is a region around a charged particle that can exert a force on another charged particle. If a charged particle is in the electric field of another charged particle, the first particle is attracted or repelled by the electric force.

Charging Atoms Atoms can become charged by gaining or losing electrons. If an atom loses electrons, is it positively or negatively charged? What about if an atom gains electrons?

Using friction to charge objects Friction can cause electrons to be “wiped” from one object and transferred to the other (for example rubbing a balloon against your hair).

Using conduction to charge objects Charging by conduction happens when electrons are transferred from one object to the next by direct contact (for example touching a negatively charged plastic ruler to an uncharged metal rod)

Charging by induction This occurs when charges in an uncharged object are rearranged without direct contact with a charged object. For example a negatively charged balloon that is close to a neutral wall will repel the electrons away from it.

Conservation of charges: When you charge objects by any method, no charges are created or destroyed Detecting charge: A device called an electroscope can determine if an object has a charge.

Conductors A conductor is a material in which charges can move easily. Most metals are good conductors because some of the electrons in metals are free to move about. Copper, silver, and aluminum

Insulators An insulator is a material in which charges cannot easily move. In insulators electrons are tightly bound to the atoms and cannot flow freely. Plastic, rubber, glass, wood

Static Electricity Static Electricity is the buildup of electric charges on an object. Static means not moving: the charges that create static electricity do not move away from the object that they are stuck to.

Electric Discharge Electric Discharge is when the charges that build up as static electricity on an object eventually leave the object. Sometimes this happens slowly (clothes stuck together will eventually transfer electrons to water molecules in the air) Sometimes this happens quickly and may be accompanied by a flash of light, shock, or cracking noise. Give an example of an electric discharge…

Lightening This is a dramatic example of electric discharge. Benjamin Franklyn first to discover lightening as a form of electricity, he also developed the lightening rod ( a pointed rod connected to the ground by a wire). What are some dangers of lightening?

Electrical Energy Electrical Energy is the energy of electric charges. Electrical energy provides people with many comforts and conveniences, such as being able to watch tv, turn on a light…etc One common way to produce electric current is through chemical reactions in a battery.

Batteries & Cells A cell is a device that produces an electric current by converting chemical energy into electrical energy. A battery converts chemical energy into electrical energy and is made up of several cells. Every cell contains a mixture of chemicals that conduct a current. These are known as electrolytes.

Cells cont. Cells also contain electrodes. Electrodes are the parts of cells where charges enter or exit.

Types of Cells Wet Cells: Dry Cells: Contain liquid electrolytes Car Batteries are examples Dry Cells: Contain electrolytes that are solid or pastelike Portable radio cells, and flashlights are examples of these.

Potential Difference Potential Difference is the energy per unit of charge. It is measured in volts. The greater the potential difference the greater the current.

Photocells and Thermocouples These are two other ways that electric energy can be converted. Photocells: Part of solar panel that converts light to electric energy. Thermocouples: Think “thermal”. Uses thermal energy to convert to electrical energy.

Quiz 17.1 The type of cell that contains liquid electrolytes are a. Wet Cells b. Dry Cells The buildup of an electric charge in an object is known as: a. electric current b. static electricity c. conductors d. insulators ________ converts chemical energy into electrical energy. (battery or photocell)

Quiz 17.1 An object becomes charged when the atoms in the object gain or lose: a. Protons b. Neutrons c. Electrons d. All of the above If two charges repel each other the two charges must be: a. positive and positive b. positive and negative c. negative and negative d. either (a) or (b)

Electric Current Current is the rate at which charge passes a given point. The unit for current is ampere “amp” (A) The two types of electric current are (AC) alternating current and (DC) direct current. In AC the charges continually switch from flowing in one direction to the reverse. Outlets in your home In DC the charges always flow in the same direction. Current from batteries and cells

Voltage The current in a wire is determined by voltage. Voltage is the difference in energy per unit of charge as it moves between two points in the path of a current. Voltage is another word for potential difference.

Voltage can vary Electrical voltage in U.S. for electrical outlets usually supply a voltage of 120V, where a portable radio only needs 3V they run easily on batteries. Did you know that electric eels can create a voltage of 600 V!!

Resistance Resistance (R) is the opposition to the flow of electric charge, and is expressed in ohms. Think “electrical friction” Good conductors = low resistance Good insulators = high resistance Resistance is also effected by thickness and length of wires, and also by temperature.

Ohm’s Law German school teacher Georg Ohm determined that the relationship between current (I), voltage (V) and resistance (R) could be expressed with the following equation: amperes = volts ohms

Electric Power Electric Power is the rate at which electrical energy is used to do work. Power = voltage x current P = V x I In units: watts (W) = volts (V) x amperes (A)

Watts the difference??? Watt is the difference between a 60W light bulb and a 120W light bulb? Answer: As power increases the bulb burns brighter, so 120W will be brighter than 60W

Electric Circuits A circuit is a complete closed path through which electrical charges flow. Circuits contain an energy source (battery), a load (light bulb), and wires to connect the two together.

Types of Electric Circuits Series Circuits: all parts are connected in a single loop Parallel Circuits: different loads are located on separate branches, and charges will travel through more than one path. Most household circuits are parallel.

Quiz 17.2 Charges flow easily in a(n) _______ (insulator, conductor) _________ is the opposite to the flow of electric charge. (Resistance, Electric power) A ________ is a complete closed path through which charges flow (load, circuit)

Quiz 17.2 cont. What type of current comes from the outlets in your home? a. direct current b. alternating current c. electric discharge d. static electricity What are the three parts of a circuit? a. energy source, load, wires b. energy source, electricity, battery c. energy source, conductors, wires d. electricity, insulators, battery