Transcript Chapter 6
Chapter 6 Ohm’s Law, Work, Energy and Power Resistance 4Ω Current Voltage 4A 16V Resistance Current Voltage 4Ω 2A 8V Resistance Current Voltage 5Ω .2A 1V Try to do in your head without a calculator Resistance Current Voltage 4mΩ 4mA 16uV Resistance Current Voltage 4MΩ 5uA 20uV Resistance Current Voltage 2kΩ 3mA 6V Resistance 2Ω Current Voltage 3A 6V Resistance Current Voltage __kΩ 3A 6V Resistance 5Ω Current Voltage 2mA 10mV Resistance .000005 Current Voltage __MΩ 2mA 10mV Resistance .005 __kΩ Current Voltage 2mA 10mV Resistance Current Voltage 2mA 10x10-4V .0000005 __MΩ 5 x 10-7MΩ Random Video of the Day Work What is work? Motion must take place for work to take place Work takes place when electrical energy is converted to mechanical energy and vice versa What is the unit for work? Joule (J) (This is also the same unit for Energy) What about electrical work? (no motion involved?) 1 Joule = Energy required to raise 1 Coulomb of charge through a potential difference of 1 Volt Work What is the equation for work? W=Q*V Work = Charge * Voltage Joules = Coulombs * Volts Power What is Power? Power is how much work can be done in a specific amount of time (Like MPH) Units for Power is Watts (W) (Like MPH) P = Work / Time Power Equation for Power Power = Work / Time Remember Power = Q * V / Time W = Q*V Power = I * Time * V / Time Remember Power = I * V I = Q/t Thus Q = I*t Power = Voltage * Current P=V*I Power See how Power also equals: P = V2/R P = I2 * R P=V*I P = V2/R P = I2 * R Power P = ? Watts I = 6 Amps V = 3 Volts P = 18 Watts Power P = 18 Watts I = 6 Amps V = 3 Volts R=?Ω R = .5 Ohms P=V*I P = V2/R P = I2 * R P=V*I P = V2/R P = I2 * R Power P = ? Watts P = 250 Watts I = 5 Amps V = ? Volts R = 10 Ohms V = 50 Volts Power P = ? Watts V = 3 Volts R=9Ω P = 1 Watts P=V*I P = V2/R P = I2 * R Power P = 32 Watts R=2Ω I=?A I = 4 Amps P=V*I P = V2/R P = I2 * R Power P=? I=? P = 20W I = 2A P=V*I P = V2/R P = I2 * R Power P=? R=? P = 2W R = 50 Ohm P=V*I P = V2/R P = I2 * R 600kwHr = $107.57 600kwHr = $96.46 April 2014 Sept 2014 14¢ 0 - 426kWh 31¢ 27¢ 19¢ 851+ 553 – 851 kWh 426 - 553kWh kWh Oct 2014 600kwHr = $108 Practical Ohm’s Law Questions 1. A load operates at 48V and draws 30mA. What is its resistance? 2. What voltage is dropped across a 1MΩ resistor when 6uA of current is flowing through it? 3. A device draws 2.5A from a 100V source. What current will it draw from a 200V source? 4. If a DC power supply can deliver 2A of current at 12V, what is the maximum available power? 5. The voltage drop of a 22kΩ resistor is 18V. How much power is the resistor dissipating? 6. A 50Ω load dissipates 100W of power. How much voltage is across the load? 7. How much current does a 60W light bulb draw from a 120V source? 8. How much will it cost to light a 13W light bulb for 30 days at a cost of $0.18 per kWhr? 9. Calculate the maximum voltage drop a 1kΩ, ¼ watt resistor should handle in constant operation? Assume a 100% safety factor. 10. How much current for the resistor above?