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Transcript
Electric Current What is electrical current? • When electrical charges move, they are known as electric current • Electrical current is the flow of electrons through a substance (a conductor). • Usually, it is the flow of electrons through wires Conductors and Insulators: • Conductors - materials through which charges move easily – metals (especially copper and aluminum) • Insulators - materials through which charges will not move easily – glass, dry wood, most plastics, rubber, dry air The two types of electrical current: • Direct Current (DC) – electrons flow only in one direction (battery powered devices) • Alternating Current (AC) – electrons move back and forth (plug-in outlet devices) Circuits: • A series of conductors moving current around is known as a circuit • Circuits must have a completely closed “loop” for current to flow • If there is a break in the circuit, current cannot travel Batteries and DC • In a DC circuit, electrons flow from negative to positive. Fan motor etc. +++ +++ ----- AC Current • In circuits with alternating current (AC), the electrons move back and forth in the wires • AC is produced by a generator which is sometimes far from the point of use. flow of current Properties of Electrical Current: • Voltage (V) – a measurement of the amount of force driving electrical current through a circuit • Voltage is measured in volts (V) • Voltage is also known as electric potential Properties of Electrical Current: • Current (I) – a measurement of the amount of electricity flowing through a circuit • Current is measured in Amperes (A or Amps) • more voltage more current Properties of Electrical Current: • Resistance (R) – a measurement of how hard it is for electrical current to flow through a circuit • Resistance is measured in the unit Ohms () • Anything in a circuit that slows current down, such as an appliance, a bulb, or an insulator is called a resistor Hose Analogy: • Compare water flowing through a hose to current flowing through a wire: – Voltage is the water pressure – Current is how much water flows through the hose – Resistance is anything that slows the water down (hose diameter, blockages, “kinks”) voltage resistance current Ohm’s Law: I = V÷R V = I×R V = voltage (V) I = current (Amps) R = resistance () R = V÷I Ohm’s Law Problem #1 1. A 9 volt battery is placed in a circuit with 2 ohms of resistance. How much current flows in the circuit? Given Unk Equation V=9v I=? I = V÷R R=2Ω Solution I = V÷R I=9÷2 I = 4.5 A Ohm’s Law Problem #2 2. A circuit with a 12V battery produces a current of 3.2 Amps. How much resistance is in the circuit? Given Unk Equation V = 12v R=? R=V÷I I = 3.2A Solution R = V÷I R = 12 ÷ 3.2 R = 3.75 Ω Ohm’s Law Problem #3 3. A circuit with 0.75 of resistance has a current of 2.0 Amps running through it. What amount of voltage is in the circuit? Given Unk Equation R=0.75 Ω V=? I=2.0 A V=I×R Solution V = I×R V = 0.75 × 2.0 V = 1.5 v Problems to solve: 1. A 9.0V battery is in a circuit with a bulb that provides 1.5 of resistance. What amount of current flows in the circuit? 2. 4.0A of current flow through a circuit with 30.0 of resistance. What is the voltage of the power source? 3. A battery provides 1.5V of potential to a circuit with a motor. If the circuit draws 0.55A of current, what resistance does the motor provide?