* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Electromotive Force
Survey
Document related concepts
Electric battery wikipedia , lookup
Regenerative circuit wikipedia , lookup
Index of electronics articles wikipedia , lookup
Josephson voltage standard wikipedia , lookup
Valve RF amplifier wikipedia , lookup
Schmitt trigger wikipedia , lookup
Operational amplifier wikipedia , lookup
Voltage regulator wikipedia , lookup
Electrical ballast wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Power electronics wikipedia , lookup
Power MOSFET wikipedia , lookup
Current source wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Current mirror wikipedia , lookup
Opto-isolator wikipedia , lookup
Surge protector wikipedia , lookup
Transcript
Internal Resistance in EMF The voltage measured between the terminals of the battery is called the terminal voltage Vt. Most batteries of some internal resistance so the terminal voltage is lower than the voltage of the EMF when the battery is discharging. When charging a battery, the terminal voltage is higher than the voltage of the EMF. 𝑉𝑡 = 𝑉 − 𝐼𝑟 Discharging battery 𝑉𝑡 = 𝑉 + 𝐼𝑟 Charging battery Circuit Analysis: Kirchoff’s Junction Rule A junction is a point in the circuit where multiple wires join together. The junction rule is based on the conservation of charge. The junction rule is: the total current entering the junction is equal to the total current leaving the junction. Circuit Analysis: Kirchoff’s Loop Rule A closed loop in a circuit is starting from one point in the circuit and going around the circuit to end where you started. Kirchoff’s Loop Rule is based on the conservation of energy. The energy that is supplied by the EMF is used by the devices in the circuit. Kirchoff’s Loop Rule: For any closed loop around the circuit the total of the potential rises is equal to the potential drops. The current through a resistor is in the direction of a potential drop since the resistor dissipates energy. The + sign to on the left of each resistor means that side is a higher potential than the right side of the resistor which has the – sign. Applying Kirchoff’s Laws Reasoning Strategy Applying Kirchhoff’s Rules 1. Draw the current in each branch of the circuit. Choose any direction. If your choice is incorrect, the value obtained for the current will turn out to be a negative number. 2. Mark each resistor with a + at one end and a – at the other end in a way that is consistent with your choice for current direction in step 1. Outside a battery, conventional current is always directed from a higher potential (the end marked +) to a lower potential (the end marked -). 3. Apply the junction rule and the loop rule to the circuit, obtaining in the process as many independent equations as there are unknown variables. 4. Solve these equations simultaneously for the unknown variables. Measuring Current A device to measure current is called an ammeter. The ammeter must be connected in series for the current to be measured. In a series circuit, the current is the same in each device. An ideal ammeter has an internal resistance of r = 0 Ω so the ammeter does not affect the current. Measuring Voltage A device that measures voltage is called a voltmeter. A voltmeter is connected in parallel to the part of the circuit to measure the voltage. Devices connected in parallel have the same voltage across them. An ideal voltmeter will have an internal resistance r = ∞ to prevent current from running through the meter and changing the voltage on the device. 20.4 Electric Power ELECTRIC POWER When there is current in a circuit as a result of a voltage, the electric power delivered to the circuit is: P IV SI Unit of Power: watt (W) Many electrical devices are essentially resistors: P I IR I 2 R V2 V P V R R 20.4 Electric Power Example 5 The Power and Energy Used in a Flashlight In the flashlight, the current is 0.40A and the voltage is 3.0 V. Find (a) the power delivered to the bulb and (b) the energy dissipated in the bulb in 5.5 minutes of operation. 20.4 Electric Power (a) (b) P IV 0.40 A3.0 V 1.2 W E Pt 1.2 W 330 s 4.0 102 J Practice Questions on Electric Power Refer to Textbook Page 573 Questions 24, 25, 27, and 28