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Transcript
SNC 1D0 Monday November 29 OHM’s Law -Electrical Resistance -Short Circuit -Ohm’s Law -GUESS Method -Practice Questions Electrical Resistance – the ability to impede (obstruct) the flow of electrons. Symbol = R Unit = Ohm (Ω) When electrons flow through a resistor, it causes a loss of electric potential (voltage drop) Short Circuit • Electrons are lazy, they will take the path of least resistance • Electrons are allowed to flow through the circuit without a load, they return to the cell without losing voltage • May become hot and cause fire (i.e. starting a fire with a battery) Ohm’s Law – the potential difference between two points on a conductor is proportional (directly related) to the electric current flowing through the conductor. V=IxR V = electric potential (voltage drop) (V) I = electric current, (A) R = electrical resistance (Ω) Rearranging the Equation V=IxR GUESS Method Given – write down the information given in the question Unknown – write down the information you need to find Equation – write down the equation you will use to solve the question Solution – substitute and solve your solution Statement – make a therefore statement Question: What is the voltage drop across the tungsten filament in a 100-W light bulb? The resistance of the filament is 144 and a current of 0.833 A is flowing through it. Practice – use the GUESS method 1. Copy and complete the table: Resistance () 25 72 Voltage (v) 30 Current (A) 30 2.5 0.25 2. If the current through a 25 resistor is 0.2 A, what is the voltage drop? 3. The voltage drop across a 18 resistor is 6 V. Find the current through the resistor. 4. An electric clothes dryer is connected to a 230 V source of electric potential. If the dryer has a resistance of 9.2 , calculate the current that it draws. 5. An electric kettle is connected to a 120-V outlet and has a resistance of 9.6 ohms. What is the current required to operate the kettle? Classwork/Homework 1. Answer questions 3, 5, 6, 7 from page 458- 464 (Ohm`s law)