* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Current Electricity * Learning Outcomes
Wireless power transfer wikipedia , lookup
Electric power system wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Three-phase electric power wikipedia , lookup
Electric machine wikipedia , lookup
Flexible electronics wikipedia , lookup
Electrical ballast wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Opto-isolator wikipedia , lookup
Current source wikipedia , lookup
Electrical substation wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Power engineering wikipedia , lookup
Buck converter wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Stray voltage wikipedia , lookup
Electrification wikipedia , lookup
Ground (electricity) wikipedia , lookup
History of electric power transmission wikipedia , lookup
Galvanometer wikipedia , lookup
Rectiverter wikipedia , lookup
Skin effect wikipedia , lookup
Overhead power line wikipedia , lookup
Mains electricity wikipedia , lookup
1 Current Electricity – Learning Outcomes Test electrical conduction in a variety of materials, and classify each material as a conductor or insulator. Set up a simple electric circuit. Use appropriate instruments to measure current, potential difference (voltage) and resistance, and establish the relationship between them. Demonstrate simple series and parallel circuits containing a switch and two bulbs. Perform simple calculations based on the relationship between current, potential difference (voltage), and resistance. 2 Test Electrical Conduction Recall the definitions of conductors and insulators: A conductor allows charge to flow through it easily (e.g. metals). An insulator does not allow charge to flow through it easily (e.g. plastic, glass). To detect if a material is a conductor or an insulator, we must know if charges can flow through it. An electric current is a flow of electric charge. 3 Test Electrical Conduction Electrical diagrams use special symbols to mean certain things: Bulb Power Supply / Battery Switch Resistor 4 Test Electrical Conduction 1. Set up a circuit with power supply, bulb, switch, and open connection in series. 2. Place an object in the open connection and check if the bulb lights. 3. Replace the object with other objects of different materials and check if the bulb lights. 5 Set Up a Simple Electric Circuit To be a circuit, there must be at least one unbroken connection between the two ends of the power supply. All circuits have a power supply, which provides a certain amount of potential difference / voltage / e.m.f. which gives energy to the circuit. The unit for potential difference is volt (V). A voltmeter is used to measure the potential difference between / across two points in a circuit. 6 Set up a Simple Electric Circuit An electric current is the flow of electric charges. The unit for current is the amp (A). An ammeter is used to measure current through a part of a circuit. 7 Set up a Simple Electric Circuit Recall that conductors allow current to flow and insulators do not. In reality, insulators are just bad conductors – i.e. they allow some current to flow, but not much. The amount of current that flows is determined by resistance. Good conductors have low resistance and bad conductors have high resistance. The unit of resistance is the ohm (Ω). Resistance can be measured with an ohmmeter. 8 Set up a Simple Electric Circuit Some devices can change their resistance to become good or bad conductors. These are called variable resistors or rheostats. They are used in e.g. dimmer switches, oven temperature scales, etc. 9 Measure Current Ammeters need to be wired in series with the object you are measuring the current through. 10 Measure Potential Difference Voltmeters need to be wired in parallel with the object you are measuring the potential difference across. 11 To Measure Resistance (Expt 30 part a) 1. Attach an ohmmeter to both ends of a coil of wire. 2. Note the resistance. 12 To Measure Resistance (Expt 30 part b) 1. Set up a coil of wire in series with an ammeter, power supply and variable resistor (or variable power supply). 2. Wire a voltmeter in parallel with the coil of wire. 3. Measure the potential difference across and current through the coil. 4. Vary the resistance of the variable resistor to get additional measurements for potential difference and current. 5. For each measurement, divide potential difference by the corresponding current and find an average. 13 To Measure Resistance (Expt 30 part b) 6. Plot a graph of potential difference vs current for the coil of wire and for the bulb. 7. Find the slope of the graph. 14 Demonstrate Series Circuits 1. Wire a power supply, switch, and two bulbs in series. 2. Note what happens to the bulbs when the switch is closed. 3. Disconnect one bulb and note what happens to other bulb. 15 Demonstrate Series Circuits Advantages: Uses less electricity than parallel. Disadvantages: One faulty component will prevent the whole circuit from working. Used in e.g. Christmas lights. 16 Demonstrate Parallel Circuits 1. Wire a pair of parallel bulbs in series with a power supply and a switch. 2. Note what happens to the bulbs when the switch is closed. 3. Disconnect one bulb and note what happens to the other bulb. 17 Demonstrate Parallel Circuits Advantages: If one component fails, the rest of the circuit still works. Disadvantages: Uses more power than series. Used e.g. in car headlights. 18 Solve Problems About Resistance Fill in the blanks in the table below using the resistance formula 𝑉 = 𝐼𝑅. Current (I) Resistance (R) Potential Difference (V) 10 5 2 200 120 30 100 2 0.5 20 120 10