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

2. Shocks from electric circuits are very serious compared to shocks from static electricity. Surprisingly small amounts of electric current are lethal. An electric current is: - the rate at which electric charges move past a given point in a circuit. The strength of the current is measured in: Amperes (A) The symbol for current in Ohm’s formula is: I Measuring Electrical Current Current (I) is measured with an ammeter.

3. 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 (like a 100W light bulb) Could suffocate 50 Adults

4. ELECTRIC POTENTIAL: VOLTAGE (V) A volt is a measure of electrical pressure and is named after the Italian scientist Alessandro Volta. The energy of each electron is called the electric potential. Electric potential is called voltage. A Voltmeter is used to measure voltage. The symbol for this unit is V.

5. RESISTANCE (R) 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). The resistance to the passage of electric current is measured with the ohmmeter. The unit is the ohm Ω, named after the German scientist George Ohm. INSULATORS have a: high resistance. CONDUCTORS have a: low resistance.

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

7. George Ohm figured out a basic law for electricity: V= Volts (electrical potential) also called “voltage drop” I= Amperes (current) R= Ohms (resistance) Ω V = I x R I = V / R R = V / I OHM’S LAW Increasing ( ↑) the voltage: increases ( ↑) the current. As resistance increases ( ↑) : the current decreases ( ↓). Ohm’s Triangle

8. 1. What is the formula for Ohm’s Law? V = I x R 2.If a water heater has a voltage drop of 240V and a resistance of 12.8Ω, what is the current? I = V / R I = 240V / 12.8Ω I = 18.75A The water heater has a current of 18.75 amps. Practicing OHM’S LAW

9. 2. If a coffee grinder has a current of 1.20A and resistance is 100Ω, what is the voltage? V= I x R V= 1.20A x 100 Ω V= 120V The coffee grinder has a voltage of 120V. 3.If a food dehydrator has a voltage of 320V and has a current of 18.5A, what is the resistance? R= V/I R= 320V / 18.5A R= 17.29 Ω The dehydrator has a resistance of 17.29 ohms. 4. If the current of a walkman is 4.7 A and the resistance is 26Ω, what is the voltage? V= I x R V= 4.7A x 26 Ω V= 122.2V The voltage of the walkman is 122.2V.