* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download document
Survey
Document related concepts
Operational amplifier wikipedia , lookup
Electric charge wikipedia , lookup
Power electronics wikipedia , lookup
Power MOSFET wikipedia , lookup
Nanogenerator wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Current source wikipedia , lookup
Opto-isolator wikipedia , lookup
Current mirror wikipedia , lookup
Surge protector wikipedia , lookup
Transcript
cell ☺ ☺ ☺ energy ☺ electron ☺ ☺ ☺ ☺ lamp ☺ ☺ ☺ Coulomb of charge (electrons) Think of it as a “bag of electrons” (containing 6250000000000000000 electrons!) ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺☺ ☺ ☺ ☺ ☺ ☺☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ Current ☺ ☺ ☺ ☺ ☺ ☺ I’m counting how many coulombs of electrons go past me every second ☺ The number of Coulombs flowing A past a point in the circuit every second. ☺ ☺ ☺ ☺ 1 Amp = 1 coulomb per second Voltage(emf) ☺ ☺ ☺ V ☺ ☺ ☺ I’m checking the difference in energy (per coulomb) between the 2 red arrows ☺ ☺ ☺ ☺ ☺ 1 Volt = 1 Joule per coulomb Voltage (p.d.) ☺ ☺ I’m checking the difference in energy (per coulomb) before and after the lamp ☺ ☺ ☺ ☺ V ☺ ☺ ☺ ☺ ☺ 1 Volt = 1 Joule per coulomb Draw the sentence 1. Electricity is the flow of electrons. 2. We measure the quantity of electrons in Coulombs. 3. One Amp means one Coulomb of electrons flows round every second. 4. The electrons carry energy from the cell to the lamp. 5. The electrons then return to the cell to get more energy. 6. The electrons are NOT used by the lamp. 7. Voltage measures the amount of energy each coulomb receives or gives. 8. Physics is the most important subject Science subject! Cell and battery of cells d.c. power supply a.c. power supply Lamp Resistance of a filament lamp • Resistance increases as the current increases (because the wire gets hot) Voltage Current open switch Ammeter Voltmeter Resistor Variable resistor (rheostat) Bell/buzzer Thermistor • Resistance decreases with increasing temperature Resistance Temp Light-dependent resistor (LDR) • High resistance in the dark but a low resistance in light Diode • Allows current to flow in one direction only (from + to – in the direction of the “arrow) Current ☺ ☺ ☺ Can you COPY the blue writing please? ☺ ☺ ☺ I’m counting how many coulombs of electrons go past me every second ☺ The number of Coulombs flowing A past a point in the circuit every second. ☺ ☺ ☺ ☺ 1 Amp = 1 coulomb per second Current I = Q/t Where I = current in Amps Q = charge (# of electrons) in Coulombs t = time in seconds In a series circuit Current is the same at any point in the circuit 2.5 A 2.5 A 2.5 A 2.5 A In a parallel circuit The current splits (total current stays the same) 2.5 A 2.5 A 1.25 A 1.25 A Milliamps! 1 A = 1000 mA 1 mA = 0.001 A Current ☺ ☺ ☺ ☺ Can you copy this please? ☺ ☺ I’m counting how many coulombs of electrons go past me every second ☺ The number of Coulombs flowing A past a point in the circuit every second. I = Q/t ☺ ☺ ☺ ☺ 1 Amp = 1 coulomb per second Voltage(emf) ☺ ☺ ☺ V ☺ ☺ ☺ I’m checking the difference in energy (per coulomb) between the 2 red arrows ☺ ☺ ☺ ☺ ☺ 1 Volt = 1 Joule per coulomb Voltage (p.d.) ☺ ☺ I’m checking the difference in energy (per coulomb) before and after the lamp ☺ ☺ ☺ ☺ V ☺ ☺ ☺ ☺ ☺ 1 Volt = 1 Joule per coulomb Voltage Voltage is the amount of energy transferred (changed) per coulomb of charge. 1 Volt = 1 Joule per coulomb A voltmeter connected across the component In a series circuit The sum of the voltages across the lamps equals the voltage across the cells 9V 3V 3V 3V In a parallel circuit In a simple parallel circuit, voltage across each lamp equals the voltage across the cells 5V 5V 5V Resistance Measures how difficult it is for current to flow. Measured in Ohms (Ω) V Resistance = voltage/current A R = V/I Ohm’s Law • V = IR V I X R Resistance of a lamp Vary the voltage and current using a variable resistor (rheostat). Plot a graph of resistance against current V Resistance = voltage/current A R = V/I Power The amount of energy used by a device per second, measured in Watts (Joules per second) A V Power = voltage x current P = VI Example • A 200 W television is plugged into the 110V mains. What is the current in the television? • I = P/V = 200/110 = 1.8A P V I X Total energy So the total energy transformed by a lamp is the power (J/s) times the time the lamp is on for in seconds, E = VIt E = energy transformed (J) V = Voltage (also called p.d.) I = current (A) t = time (s) Example • A kettle uses 240V and 8A. What is its power? • P = VI = 240x8 = 1920W (=1.9kW) • How much energy does the kettle use in 5 minutes? • E = VIt = 240x8x300 = 576000 J P V I X Alternating current • Current changes direction 50 times a second. Fuse • Thin piece of wire which melts if the current is too high • If a fault develops, this thin piece of wire melts if the current is too high • Circuit breakers are sometimes used instead Earth wire • Connects metal body of appliance to earth • If a live wire comes loose, current flows to earth and blows the fuse Double insulation • Some appliances have no earth wire because they have a plastic outer case • The plastic case acts as an extra layer of insulation around the wires Electrostatics 1. There are two types of electric charge (positive and negative) Hi! Hola! Electrostatics 2. Opposites attract Electrostatics 3. Static charges can be produced by the action of friction on an insulator Plastic, amber, glass, Perspex Electrostatics 4. Electrons are negatively charged Electrostatics http://phet.colorado.edu/sims/balloons/balloons_en.jnlp 5. Objects are charged positive by the loss of electrons cloth Electrostatics 6. Objects are charged negative by the gain of electrons Only electrons move, that’s why they call it electricity! cloth Electrostatics YouTube - Refueling Fire Caused by Static Electricity 7. Static charges can be dangerous Electrostatics 7. Static charges can be dangerousYouTube - Gas Station Fire, Static Electricity Starts a Flash Fire. Electrostatics 8. Static charges can be useful Electrostatics 8. Static charges can be useful Electrostatics YouTube - Bill Nye the Science Guy - 25: Static Electricity 1/3 YouTube - Mitsuba Systems - Sprayright Series 700 Powder Spray System 8. Static charges can be useful Draw the sentence 1. 2. 3. 4. 5. 6. 7. 8. There are positive and negative charges Opposite charges attract and like charges repel Static charges can be made by the action of friction on an insulating material Electrons are negatively charged Objects are charged positively by the removal of electrons Objects are charged negatively by the addition of electrons Static electricity can be dangerous (aeroplane refueling and gas stations) Static electricity can be useful (painting, photocopiers and removal of smoke from chimneys)