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CIRCUITS

CIRCUITS. What we know... Current is the flow of charge It can be the flow of positive (conventional current) It can be the flow of negative (electron current)

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CIRCUITS

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  1. CIRCUITS

  2. What we know... • Current is the flow of charge • It can be the flow of positive (conventional current) • It can be the flow of negative (electron current) • Current can be visualised as the amount of water that falls down a waterfall every second (Current in A equates to the amount of charge passing through a point per second)

  3. What we know... • Voltage is the amount of energy given to • each coulomb of charge • Is also known as EMF • The Voltage is given to a charge by a source • of EMF such as a battery • Voltage is the measure of electrical potential energy. It can be visualised as changing the height of a waterfall. The higher the fall the greater potential energy the water will gain, hence the greater amount of work it can do. By increasing the potential of the charge (or water) it can do more work.

  4. VOLTAGE V = W/q V = Voltage in Volts (V) W = Work in J q = Charge in Coulombs CURRENT I = q/t I = Current in Amperes (A) q= charge in coulombs t = time

  5. ELECTRICAL POWER Power is the rate of doing work (releasing energy). Therefore a charge with higher potential energy (Voltage) has the potential to do more work P = VI The energy used by something depends on the rate of use of that appliance E = Pt = VIt E = Energy is Joules P = Power in watts t = time in seconds V = Voltage in V I = Current in A

  6. ELECTRICAL CIRCUITS Series Series circuits only have one possible path for the current to flow. Same current flows through all parts in the circuit Voltage is shared by the parts in the circuit Parallel Parallel circuits have more than one possible path for the current to flow. The current is shared by all parts in the circuit. These will add to the total current

  7. 6.0Ω 4.0Ω 2.0Ω 24V Calculate total resistance Calculate the current flowing in each resistor Calculate the voltage across each resistor Rt = R1 + R2 + R3 = 4 + 2 + 6 = 12Ω I = V/R = 24/12 = 2 A V = IR = 2 x 4 = 8 V V = IR = 2 x 2 = 4 V V = IR = 2 x 6 = 12V The voltage adds up to the voltage supplied

  8. 12V Calculate total resistance Calculate the current in each resistor 1/Rt = 1/R1 + 1/R2 + 1/R3 = ½ + 1/3 + ¼ = 6/12 + 4/12 + 3/12 = 13/12 = 12/13 = 0.92 Ω Each resistor has V of 12V across it I = V/R = 12/2 = 6 A I = V/R = 12/3 = 4A I = V/R = 12/4 = 3A Vt = IRt = 13 x 0.92 = 12V therefore correct

  9. Complete the following Three resistors are connected to a DC power supply as shown. When all the switches are closed it is found that the current in the 20Ω resistor is 500mA Calculate the total resistance of the circuit b) The potential difference across each resistor c) The current in the 6Ω resistor d) The voltage of the DC supply 6Ω 12Ω 0.5A 20Ω

  10. 6Ω and 12Ω resistors are in parallel 1/Rt = 1/R1 + 1/R2 = 1/6 + 1/12 2/12 + 1/12 = 3/12 = 12/3 = 4Ω Rt = 4Ω + 20Ω = 24Ω Total R of parallel section is 4Ω V = IR = 0.5 x 4 = 2 V V = IR = 0.5 x 20 = 10 V The voltage across the 6Ω and 12Ω resistors is 2V. Across the 20Ω resistor it is 10V The 6Ω resistor has 2V across it I = V/R = 2/6 = 0.33A The voltage of the supply is equal to the voltage across the resistors in series V = 10 + 2 = 12V

  11. ELECTRICITY IN THE HOME

  12. We already know what Conventional Current and electron current is... In the household there are generally two types DIRECT CURRENT (DC) Refers to a current supply where the flow of charge is always in one direction (like from a battery) ALTERNATING CURRENT (AC) Refers to a current supply where the flow of charge alternates back and forth (like from the household mains)

  13. AC POWER SUPPLY • This power supply is used in homes and businesses. It has a number of advantages over DC. • More easily produced • Safer and cheaper for most applications] • Easily transformed to higher or lower voltages • Suitable for precision devices such as clocks because its frequency can be controlled • Can be transmitted at high voltages to minimise energy losses

  14. How AC and DC current is generated

  15. Check out this page, got some cool stuff on it http://mods-n-hacks.wonderhowto.com/ If we have some time we can experiment around with some of the things they have on this site!!!!

  16. ELECTRICITY IN THE HOME Electricity is supplied to our homes usually in single phase 240V AC The cable is connected to the houses fusebox (switchboard) There are two insulated wires, one the active, the other neutral The active wire is connected through the meter to the main switch and then to a different circuit each with their own fuse. The neutral wire is earthed by connecting it to a metal pipe or similar

  17. Active Neutral Earth

  18. CIRCUITS IN THE HOME Lights in the home are set up in parallel so that each light recieves the full mains voltage (240V) Each light can be switched on or off independently of the others. Live Neutral

  19. CIRCUITS IN THE HOME Power points are on a separate circuit of their own and a wired in parrallel. This allows full mains voltage (240V) and independent switching. An earth wire is also put into these connections, this wire connects the case of the appliance to the earth which will prevent electrocution in the case of the appliance becoming “live”. Appliance Case Earth Live Neutral

  20. SAFETY FEATURES IN THE HOME Earth Wire: It connects the metallic case of an appliance to the ground. If the appliance becomes live the current will flow through to the earth rather than through the person. A fuse will most likely blow Fuses: Fuses are made from low melting point wires which melt (blow) if a too larger current goes through the circuit Circuit Breakers: Ensure current in a circuit does not go over a particular level. If current exceeds level the circuit is broken. These are preferred to fuses as they work instantaneously and are easily reset. RCD: A RCD is able to detect and differecne between the acitive and neutral wires which could be caused by a fault or grounding of a live wire, a difference of as little as 30mA will trip this circuit breaker in milliseconds Double Insulation: Some appliances (eg hair dryer) have a layer of insulation over the live components (wires) and then another layer of plastic over the top. No earth wire

  21. Idiotic behaviour with electricity http://www.youtube.com/watch?v=yiM_LMxUQrs Idiotic behaviour with electric fences http://www.youtube.com/watch?v=exyW-vmVnQo

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