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Grade 9 Academic Science – Electricity Resistance and Ohm’s Law Section 13.7 Electrical resistance is the opposition to the movement of electrons as they flow through a circuit. An ohmmeter is used to measure the resistance. It is placed in series across a load. A resistor is an electrical device that reduces the current in a circuit. Resistors have may uses. Light weight carbon resistor are used in electronics, variable resistors are used as dimmer switches, and ceramic resistors are used in big circuits (high voltage lines – metal electrical towers). Current, Voltage and Resistance – Ohm’s Law Activity: Test the relationship between current and voltage with two different resistors Potential Difference (V) Current At Resistor A (A) Current at Resistor B (A) 0 1 2 3 4 5 Ohm’s Law states that as the potential difference increases, so does the current. When graphed there is a straight line relationship between voltage and current. The slope of a V / I graph is the resistance. The relationship among current, potential difference and resistance can be written mathematically as the equation I = V / R Sample A load has 1.2 A of current running through it. The voltage across the load is 6.0 V. Calculate the resistance. Use Ohm’s Law…re-arrange the formula to solve for resistance. Practice / Homework -- Try the practice word problems on Page 568, Questions 1-9, Page 570