Electricity
Physical Science - Middle School
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Study Guide Electricity Physical Science - Middle School
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ELECTRICITY Charged Particles Electric charges are either positive (+) or negative (-). The protons in an atom have a positive charge and the electrons around the atom have a negative charge. If two particles have similar charges, they repel each other, but, if they have opposite charges, they attract each other. This explains why an atom holds together. The positively charged protons in the nucleus exert a strong attraction for the negatively charged electrons that surround it. LESSON CHECKPOINT: What is the interaction between charged particles? States of Electricity When electric charges build up on an object but do not move, this is called static electricity. An example of this is what causes lightning. As the picture below shows, an excess number of positive charges builds up on the ground while a large number of negative charges builds up in the clouds. At a certain point, the difference between the negatively charged cloud and the positively charged earth gets so great that static electricity turns into an electrical current. The actual bolt of lightning is a discharge of electrons traveling at the speed of light toward the positive charges. LESSON CHECKPOINT: What is the difference between an electrical current and electricity? © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Charged Particles in Motion This flow of electrons from one place to another is called electricity, an electrical current or electrical energy. In order for this flow to occur, there has to be an electrical circuit or pathway. As long as the circuit is complete, electricity flows, but when the circuit is broken, the current stops. The strength of an electric current is measured by the number of electrons that flow in the circuit. We measure current in amperes or amps. The more electrons that flow in a circuit, the greater the number of amps. The potential for electricity to flow is referred to as voltage. The greater the difference between the positive and negative parts of the circuit, the more potential for the attraction that causes a current to flow, and thus the higher the voltage. This potential is measured in units called volts. There is always some resistance to an electric current. This resistance is measured in units called ohms. When resistance increases, it makes it more difficult for the current to flow. Conductors, like wire, have much less resistance than insulators like wood. LESSON CHECKPOINT: What are the terms for electric potential, electric current and electrical resistance? © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Ohm’s Law The mathematical relationship between volts, amps, and ohms is called Ohm’s Law. The formula for this law is shown below: I=E/R or amperage equals voltage divided by resistance. Notice how this law confirms what we were just saying about electrical resistance. If the resistance increases and the potential does not change, the result is a decrease in amperage. Types of Circuits The two types of electrical circuits are series and parallel. The diagram below shows both types. Notice that in a series circuit, if a break occurs anywhere in the circuit, no electricity will flow. If bulb 1 was taken out, bulbs 2, 3 and 4 would not light. On the other hand, in the parallel circuit, a break in one place does not necessarily mean that the current would stop. For example, if light bulb 1 were taken out, electricity would still be able to flow through bulbs 2 and3. LESSON CHECKPOINT: What is the difference between a series and a parallel circuit? © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Electrical Power Electrical power is measured in units called watts. The formula for calculating wattage is shown below: Power= voltage x current OR P= V x I The formula tells us that by increasing either the potential or the actual amount of current, we will increase the wattage. Batteries Batteries are electrochemical cells. In an electrochemical cell, chemical energy is converted to electrical energy. In the dry cell battery shown below, an electrolyte causes a chemical reaction with the electrodes, zinc, and carbon. This reaction causes electrical potential to build up and a current to flow through the electrolyte. So when you connect a battery to an appliance or tool that uses batteries, you provide connection to an electrical current that can generate electrical power. When batteries go bad they sometimes leak this electrolyte paste. LESSON CHECKPOINT: How does a dry cell battery work? © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Safety Reminders While working with electricity, safety should always be kept in mind. Many people are killed every year, especially in Florida, by lightning. • To avoid being struck by lightning, remember to stay away from tall trees and other tall structures if you are outside during a storm. If you are inside a home, you are normally safe from lightning but you still could be hurt by electric shocks or short circuits. • Since water conducts electricity, using dry hands while using electrical appliances is important. • Make sure your home is equipped with fuses and circuit breakers that break the electrical circuit if too much current starts to flow. LESSON CHECKPOINT: Why should you make sure your hands are not wet when using an electrical appliance such as a hair dryer? © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
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