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Name Date Electricity Section 2 Electric Current Scan Use the checklist below to preview Section 2 of your book. • Read all section titles. • Read all bold words. • Read all charts and graphs. • Look at all the pictures and read their captions. • Think about what you already know about electricity. Write two facts you discovered about electric currents as you scanned the section. 1. Accept all reasonable responses. 2. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Review Vocabulary Use the term pressure in a scientific sentence. SI International System of Units – the improved universally accepted version of the metric system that is based on multiples of ten and includes the meter (m), liter (L), and kilogram (kg) New Vocabulary Define the following key terms. electric current voltage difference electric circuit resistance Ohm’s law the rate of movement of electric charges in a single direction related to the force that causes electric charges to flow a closed path that electric current follows the tendency for a material to oppose the flow of electrons the current in a circuit equals the voltage difference divided by the resistance Academic Vocabulary Use a dictionary to define terminate. terminate coming to an end or capable of ending Electricity 71 Name Date Section 2 Electric Current Current and Voltage Difference I found this information on page . SE, p. 179 RE, p. 97 (continued) Create a drawing of an electric circuit that has a battery powering a digital clock. Show the direction of electron flow, and describe the movement of the electrons in the circuit. Accept all reasonable Accept all reasonable responses. responses. Electrons flow 12:00 away from the negative Electron flow terminal and toward the positive terminal of the Battery battery. I found this information on page . SE, p. 180 RE, pp. 97–98 Compare dry-cell batteries to wet-cell batteries. Describe the components of each type of battery. In your own words, explain how it works. Accept all reasonable responses. Battery Type How It Works Dry-cell two electrodes (carbon rod, zinc container) electrolyte (conducting chemicals in a moist paste) When the two terminals are connected in a circuit, the zinc and the electrolyte react. Electrons move to make the terminal connected to the carbon rod positive. Electrons build up on the zinc cylinder, making its terminal negative. The voltage difference between the terminals makes current flow. Wet-cell two connected plates made of different metals in a conducting solution Chemical reactions transfer electrons from one plate to the other plate, making one terminal positive and the other terminal negative. Challenge advanced students by asking them to name different types of batteries now available, and to predict how their composition might differ from standard zinc batteries. 72 Electricity Components Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Batteries Name Date Section 2 Electric Current Resistance Summarize the source of resistance in a material. I found this information on page . Accept all reasonable responses. As electrons flow through a I found this information on page . Organize the factors that affect the electrical resistance of a material. Write each word in one of the boxes below. SE, p. 181 RE, p. 99 SE, p. 181 RE, p. 99 Ohm’s Law Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. (continued) I found this information on page . SE, p. 182 RE, p. 100 Students can work with partners to derive the formulas for Ohm’s law. material, they bump into the atoms that make up the material. hotter cooler longer shorter thicker thinner More Resistance Less Resistance hotter, longer, thinner cooler, shorter, thicker Define three equations that come from Ohm’s law. Unknown Value Current Known Values Voltage difference Resistance Equation Resistance Voltage difference Current V R ! "" I Voltage difference Current Resistance V ! IR V I ! "" R S YNTHESIZE I T Electricians use different thickness of copper wire when they create the electrical circuits in a home. Use your knowledge of resistance to explain why an electrician would choose a thicker wire for a circuit that will provide power to a high-current appliance. Accept all reasonable responses. A thicker wire would have less resistance than a thinner wire. It will generate less heat than a thinner wire when conducting a high current. Electricity 73