Electricity Module (uploaded by Giserey)


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Electricity Module (uploaded by Giserey)

  1. 1.  Electric Current  Voltage  Resistance  Safety in Using Electricity
  2. 2. Grade 7 (3rd Quarter) Motion in One Dimension(in terms of displacement, speed, or velocity and acceleration) Waves (characteristics; transverse vs. longitudinal, mecahnical vs. electromagnetic) Sound (characteristic) Light (characteristic) Heat (heat transfer) Electricity (charges and charging process) Grade 8 (1st Quarter) Laws of Motion Work, Power, and Energy Sound (propagation of sound through SLG) Light (properties, characteristicsof visible light) Heat (heat and temperature; it's effect) Electricity (current- voltage-resistance relationship; electric power; electric energy; home circuitry)
  3. 3.  Activity 1 Current and Voltage  Activity 2 Current and Resistance  Activity 3 What's the Connection?  Activity 4 Stay safe!
  4. 4. How do voltage and resistance affect electric current? What are the safety precautions needed in using electricity?
  5. 5.  A circuit is any arrangement of a source of energy (battery), connecting wires, and a  load (e.g. bulbs)  A complete or a closed circuit provides a path for electrical charges to flow.  Electric current is a measure of the number of electrical charges passing through a cross- section of a conductor in a given time.  The direction of conventional current or simply current is from the positive terminal of the battery to the negative terminal.
  6. 6.  The symbol for current is capital letter I.  The unit, ampere (A), is named after Andre- Marie Ampere, a French physicist who made important contributions to the theory of electricity and magnetism.  An ammeter measures electric current. The positive terminal of an ammeter is connected to the positive terminal of the energy source (e.g. battery) while the negative terminal is connected to the negative terminal of the energy source
  7. 7.  In a circuit, work must be done on the charges to make them move.  The battery supplies the energy in electric circuits.  The chemical energy in the battery is transformed to electrical energy.  This electrical energy moves the
  8. 8.  A battery consists of several dry cells or wet cells.  Dry and wet cells contain a conducting medium called electrolyte.  (The batteries we use in flashlights and watches are dry cells.)
  9. 9.  Symbol for voltage is capital letter V.  The unit, volts (V)  Named after the Italian physicist AlessandroVolta who invented the voltaic pile, the forerunner of what we now call the dry cell.
  10. 10.   A voltmeter measures voltage.  The voltmeter should be connected across the load being tested.  The positive terminal of a voltmeter is connected to the positive terminal of the bulb while the negative terminal is connected to the negative terminal of the bulb.
  11. 11.  The more dry cells used,the brighter the bulb .  The current is higher for two dry cells as compared to one dry cell.  The bulb glows brighter when another dry cell was added to the circuit and reading on voltmeter increases.  The voltage is bigger for two dry cells as compared to one dry cell.  For a constant load (one bulb), when the voltage increases the current also increases.
  12. 12.  Dry cell provides the energy that moves the charges in a circuit  Dry cell must be connected by conducting wires to a load to form a complete circuit.  Adding dry cells in series increases the voltage in a circuit.
  13. 13.  Adding dry cells increases the current in a circuit as shown by the ammeter readings  Brightness of the bulb also indicates the amount of current passing through it.  The bigger the current through the bulb, the brighter it glows.  Both the meter readings and the brightness of the bulb show that voltage and current are related.  As the voltage increases, the current also increases.
  14. 14.  When electric charges flow through the wires and loads of the circuits they encounter resistance or a hindrance to their movement.  The symbol for resistance is capital letter R.  The unit, ohms (Ω) is named after the German physicist Georg Simon Ohm.
  15. 15.  Resistance of the material opposes the flow of charges.  Resistance can also be measured and they are expressed in units called Ohms.  A lower resistance would mean that there is less opposition in the flow of charges and therefore bigger current.
  16. 16.  Different materials have different amounts of resistance.  Conductors definitely have very little resistance and therefore allow more charges to pass through.  Insulators are materials that have very high resistance and therefore flow of charges would be difficult.
  17. 17.  For a fixed resistance (one bulb), as the voltage increases, the current also increases.  Keeping the voltage the same (2 dry cells), when the resistance increases, the current decreases. 
  18. 18.  The length and thickness of the conducting wire are factors that affect resistance encountered by current.  The longer the wire the greater will be its resistance and the greater the cross sectional area (a measure of the thickness of the wire), the lower will be its resistance.
  19. 19.  The resistance of an object also changes when the object becomes wet.  Dry human skin for instance has a resistance of 100,000 ohms but when it gets wet its resistance is reduced to 1,000 ohms.  It is important to dry the hands when plugging an electrical appliance to reduce any chance of getting a lot of current if an accident occurs.
  20. 20.  Current Reaction  below 1 milliampere Generally not perceptible  1 milliampere Faint tingle.  5 milliampere Slight shock felt not painful but disturbing.  Average individual can let go. Strong involuntary reactions can lead to other injuries.  6-25 milliampere (F) Painful shock, loss of muscular control.  9-30 milliampere (M) The freezing current or let go range individual cannot let go but can be thrown away from the circuit if extensor muscles are stimulated
  21. 21.  Current Reaction  50-150 milliampere Extreme pain, respiratory arrest (breathing stops) severe muscular contractions. Death is possible.  1,000-4,300 milliampere Rhytmic pumping action of the heart ceases. Muscular contraction and nerve damage occur, death likely.  10,000 milliampere Cardiac arrest and severe burns occur. Death is probable.  15,000 milliampere Lowest overcurrent at which a typical fuse or circuit breaker opens circuit.
  22. 22.  Series Connection  loads form a single pathway for charges to flow  A gap or a break anywhere in the path stops the flow of charges.When one bulb is removed from the socket, a gap is created.The other bulb turns off as there is no longer current in the circuit.
  23. 23.  Series Connection  The total resistance in a series circuit is equal to the sum of the individual resistances of the load (bulb).  Current is the same in every part of the circuit.  The current is equal to the voltage divided by the total resistance. As more load (bulb) is added in a series circuit, the smaller the current as reflected by the brightness of the bulb.  The voltage across each load depends on the load’s resistance.  The sum of the voltage across each load is equal to the total voltage.
  24. 24.  Parallel Connection  loads form branches; each provides a separate path for charges to flow.  A gap or a break in any branch will not affect the other branches.Thus, when one bulb is removed from the socket, a gap is created only for that branch.The other bulbs still glow as their path is still complete.  In a parallel connection the voltage is the same across each load.
  25. 25.  Parallel Connection  The total current is equal to the sum of the currents in the branches.  The amount of current is inversely proportional to the resistance of the load.
  26. 26.  Table 4 Series connection Parallel connection  Total current Same as current in individual load Equal to the sum of current in individual loads  Total voltage Equal to the sum of the Same anywhere across  voltages across each load two points in the circuit  Total resistance Increases with increasing load Decreases with increasing load
  27. 27.  Fires can happen when the wires start heating up causing combustible parts of the house to be set on fire.  The wires heat up when the current passing is more than what the wires can carry. In this case there is an overloading of the circuit.  An example of how the circuit gets overloaded is by plugging a lot of appliances in a common outlet like an extension cord.
  28. 28.  Another instance of overloading of the circuit is the presence of short circuits.  Short circuits happen when wires with defective rubber insulation touch each other so the current does not pass to the supposed path it should take.  It is a circuit where the current encounters very little resistance and therefore the amount of current will increase rapidly. Such increase in the amount of current leads to the overloading of the circuit and can lead to fires.
  29. 29.  In the wires the electrons that flow in a closed circuit collide with the atoms of the conducting wire.  As the collisions take place the kinetic energy of the metal atoms increases.  The increased kinetic energy of the atoms is dissipated as heat.  The higher the kinetic energy of the particles, the higher will be its temperature.
  30. 30.  The higher the current passing through the wire, the more collisions between the electrons and the atoms of the wire take place.  In the end the wire will become hot. So just imagine how much heat will be generated from an overloaded circuit.