advertisement

School: St. Andrew Technical High School Subject: Electrical Technology Name of Student Teacher: Jermaine Kelly Grade 8C What is Electromotive Force? • Energy per unit charge that is imparted by an energy source, such as an electric generator or a battery. What am I ? Topic for today’s lesson: Fundamentals of Ohms law. Outcome: • state the name of the scientist that observe the relationship of ohms law to 100% accuracy without using the note book. • state the definition of ohms law to 100 % accuracy without assistance from others. • Define electric current of to 100 % accuracy without assistance from others. Outcome: •describe voltage correctly without assistance from the class. •what resistance is to precision based on the explanation that is presented in class. •perform calculations using ohms law formula accurately without assistance from others The beginning of Ohms law. • Ohms law was revealed by Georg Ohm who was born March 16, 1789, in Germany, he died in July 6, 1854; Mr. Ohm is a German physicist who also bears the name of the unit of resistance. He observed the relationship among current (I), voltage (V) and resistance (R ). Definition of ohms law. Ohms law indicated that the electrical current in a circuit is directly proportional to the applied voltage and is inversely proportional to the resistance in a circuit at a constant temperature. Graph explain ohms law 3. Definition of electric current. An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire. It can also be carried by ions in an electrolyte. The unit of electric current is amps or amperes and is represented by the letter A. Definition of voltage Voltage is the pressure from an electrical circuit’s power source that pushes charged electrons (current) through a conducting loop, enabling them to do work such as illuminating a light Voltage is represented by the letter Vor E Definition of resistance. • Resistance is an electrical quantity that measures how the device or material reduces the electric current flow through it. • The resistance is measured in units of ohms (Ω). The symbol to represent resistance is R. The Formula for ohms law • V=IR • I=V/R • R = V/I Where: V - is the voltage that is measured in volts (V) I – is the current that is measured in Ampears (A). R – is the resistance that is measured in ohms (Ω). Ohms law calculations •Suppose that a circuit has 1,000 Ω of resistance with 150 V of applied voltage. What is the current ? Solution •I = V / R •I = 150 / 1000 Ω • = 0.15A Definition of electric power. •Electrical power is the rate at which electrical energy is used. The unit of electrical power is watt which is named after the scientist James Watt, and is represented by the symbol W. •There are three basic formulas to find the Electric power in a circuit. • P = IV • P = I2 R • P = V2/R Calculations • If a circuit has 50 milli -amperes of current flow and an applied voltage of 10V, how much power does the circuit dissipate? Using the basic formula for power: solution • P = IV • P = 10V ×50mA Calculations • If a circuit has a voltage of 75 V and a resistance of 15 Ω , how much power does the circuit dissipate? Using the basic formula for power: Class Activity • Instructions: Answer the following questions on a separate sheet of paper. Show all work and formulas. V = I×R • 1. What is the voltage in a circuit that has a current of 2.4 A and a resistance of 4 Ω ? • 2. A circuit has a resistance of 12 and draws a current of 6 A what is the potential difference in the circuit? • 3. A TV set uses a current of 12 A and has a resistance of 10 Ω, what is the potential difference? • 4. A toaster has a resistance of 60 Ωand is plugged into a 120 V power supply, what is the current in the toaster? Summary • What is the formula of Ohms law ? • What is name of the scientist that discovered ohms law? • What is the formula to calculate power ? • What is the unit of resistance?