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Voltage, Current, Resistance, Ohm’s Law 10.9, 10.10

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10.9 Electric Current Shocks from electric circuits are very serious in comparison to shocks from static electricity. Shocks from electric circuits are very serious in comparison to shocks from static electricity. Every year people are injured and sometimes die from electrocution. Every year people are injured and sometimes die from electrocution. Surprisingly small amounts of electric current are lethal. Surprisingly small amounts of electric current are lethal.

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Electric current is a measure of the rate at which electric charges move past a given point in a circuit. Electric current is a measure of the rate at which electric charges move past a given point in a circuit. Unit for current is Ampere (A). Unit for current is Ampere (A). Symbol in the Ohm’s Law formula for current is (I). Symbol in the Ohm’s Law formula for current is (I).

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Electric Current Human Reaction 0.001A Perception Level 0.002A Muscles Tingle 0.005A Max. SAFE Current 0.016A Muscles Contract 0.050A Ventricular Fibrillation (Fatal) 0.2A Heart/Breathing Stop (severe burns) 0.833A Could suffocate 50 Adults

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Read p 314-315 How much current do you think someone experiences when they are electrocuted (death by the electric chair)? How much current do you think someone experiences when they are electrocuted (death by the electric chair)? Why is it dangerous to try to help someone who is experiencing an electric shock? Explain what you should do if you wish to help that person? Why is it dangerous to try to help someone who is experiencing an electric shock? Explain what you should do if you wish to help that person? Page 315 - Answer questions 1, 5 Page 315 - Answer questions 1, 5

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ELECTRIC POTENTIAL: VOLTAGE (V) A volt is a measure of electrical pressure and is named after the Italian scientist Alessandro Volta. A volt is a measure of electrical pressure and is named after the Italian scientist Alessandro Volta. The energy each electron has is called the electric potential. Electric potential is commonly referred to as voltage. The energy each electron has is called the electric potential. Electric potential is commonly referred to as voltage.

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CURRENT (I) Electric current is the quantity of electricity going by a point in a circuit. Electric current is the quantity of electricity going by a point in a circuit. Current (I) is measured with an ammeter. The unit used to measure electric current is the ampere, which is named after the French physicist A.M Ampere. Current (I) is measured with an ammeter. The unit used to measure electric current is the ampere, which is named after the French physicist A.M Ampere.

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RESISTANCE (R) (p. 316) The molecules of all types of conductors impede, or resist, the flow of electrons to some extent. The molecules of all types of conductors impede, or resist, the flow of electrons to some extent. This ability to impede the flow of electrons in conductors is called electrical resistance (R). This ability to impede the flow of electrons in conductors is called electrical resistance (R).

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RESISTANCE The resistance to the passage of electric current is measured with the ohmmeter. The unit is the ohm, named after the German scientist George Ohm. The resistance to the passage of electric current is measured with the ohmmeter. The unit is the ohm, named after the German scientist George Ohm. INSULATORS oppose the flow of electric current and have a high resistance. INSULATORS oppose the flow of electric current and have a high resistance. CONDUCTORS have a low resistance. CONDUCTORS have a low resistance.

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Factors that affect the resistance of wires: 1. The thickness of wires 2. The length of wire 3. The material wire is made of 4. The temperature of the wire

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This might help… An analogy to help understand these terms is a system of plumbing pipes. The voltage (V) is equivalent to the water pressure, the current (I) is equivalent to the flow rate, and the resistance (R) is like the pipe size. An analogy to help understand these terms is a system of plumbing pipes. The voltage (V) is equivalent to the water pressure, the current (I) is equivalent to the flow rate, and the resistance (R) is like the pipe size.

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OHM’S LAW George Ohm figured out a basic law for electricity V= Volts (electrical potential) I= Amperes (current) R= Ohms (resistance) V = I x R I = V / R R = V / I

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OHM’S LAW Current is directly proportional to voltage, therefore, increasing ( ↑) the voltage increases ( ↑) the current. Current is directly proportional to voltage, therefore, increasing ( ↑) the voltage increases ( ↑) the current. The current is inversely proportional to resistance; therefore, as resistance increases ( ↑), current decreases ( ↓). The current is inversely proportional to resistance; therefore, as resistance increases ( ↑), current decreases ( ↓).

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Question What is the formula for Ohm’s Law? V = I x R V = I x R If a coffee grinder has a current of 1.20A and resistance is 100Ω, what is the voltage? 120 V

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Questions P.319 #1,2,5 P.319 #1,2,5

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A couple of extras… If the current of a walkman is 4.7 A and the resistance of 26Ω, what is the voltage? If a food dehydrator has a voltage of 320V and has a current of 18.5A, what is the resistance?

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Answers 122.2 V 122.2 V17.3Ω

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Chapter 10 Review Questions p. 328-329 p. 328-329 # 2, 3, 5, 7, 8, 10, 11, 13 and 14 # 2, 3, 5, 7, 8, 10, 11, 13 and 14

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