Analysing Electric Fields and Charge Flow


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Physics Chapter 2 Form 5, SPM

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  • Analysing Electric Fields and Charge Flow

    1. 1. 2.1 analysing electric fields and charge flows Physics form 5 chapter 2
    2. 2. Learning Outcomes • A student is able to : • •State the relationship between electron flow and electric current. • •Define electric current • •Describe and electric field • •Sketch electric field lines showing the direction of the fields • •Describe the effect of and electric field on a charge • •Solve problems involving electric charge and current
    3. 3. What is electricity?
    4. 4. • Think how electrical energy makes the electrical equipment function. • This chapter will assist you in your understanding of the concept of electricity
    5. 5. The atom • An atom is a fundamental unit of matter made up of • protons (with a positive charge) • neutrons (neutral – no charge) • electrons (with a negative charge)
    6. 6. What is electricity? • Everything is made of atoms which contain POSITIVE particles called PROTONS and NEGATIVE particles called ELECTRONS. Proton (+) Neutron Electron (-)
    7. 7. • An atom will usually have the same number of positives and negatives • This makes the atom NEUTRAL. Proton (+) Neutron Electron (-)
    8. 8. • In some materials, particularly metals, the electrons farthest from the nucleus are not bound to a particular atom - they can move freely from one atom to another. • Electricity is the flow of these free electrons in a wire
    9. 9. Electrical Charge • Electric charge is given the symbol •Q • Electrons are the charge carriers • that flow in an electrical circuit – • from the negative to positive • terminals.
    10. 10. Electric Current • Electric current consists of a flow of electrons. • The more charges that flow through a cross section within a given time, the larger the current conductor charge• Good conductors allow electrons to move • through them easily. Insulators do not allow electrons to move easily.
    11. 11. What makes these free electrons move? • Suppose we put something that has a net positive charge at the one end of the wire (say, at the right end of the wire pictured above). Let's also suppose that we put something with a net negative charge at the other end (the left end in the wire above). Then the electrons in the wire will be attracted to the positive end and repelled by the negative end. Hence, they will flow from left to right. That's electricity!
    12. 12. Electrical Charge • Charge is measured in •Coulombs • which is given the symbol •C
    13. 13. Electrical Charge
    14. 14. Electrical Charge • The charge on a proton is •1.6 x 10-19C • which is the same size as the charge on an • electron. Amount or Sum of Charge Sum of charge = number of charge particles charge of 1 particle = n x e
    15. 15. So, what is electricity? Electrons have a negative charge (Q) measured in coulombs (C). Electrons move round a circuit from negative to positive (remember like charges repel, opposites attract) giving rise to an electric current.
    16. 16. What is electricity? So electricity is… movement of electrons or flow of charge round a circuit. We call this electric current.
    17. 17. Charge, Current & Time • Electric current is given the symbol •I • Electric current is a flow of • negative charges (electrons) in a • Conductor.
    18. 18. Direction of Current
    19. 19. Charge, Current & Time • Current is rate of flow of charges OR the amount of charge flowing per second and is given the unit •Amps (A)
    20. 20. Electric Current • Unit for current is Ampere (A) • I = Q/t, • where I = current • Q= Quantity of charges (Coulombs) • t= time (second) • 1 Ampere is 1 coulomb, C in one second.
    21. 21. Measuring Current - Ammeter • To use the ammeter in the measurement of an electric current, the ammeter must be connected in series to the circuit.
    22. 22. Short Quiz 1. An electric field exists in the space surrounding a ______body. • 2. Like charges ___________ each other , unlike charges __________each other. 3. An electric current is defined as 4. ______________________________________ 5. Electric current, , (Q measured in 6. ___________, C) • 4.Electric current is measured with an ______________ in SI unit _____________ tTime QeCh I , ,arg charged repel attract the rate of flow of electric charge coulomb ammeter Ampere, A
    23. 23. Quiz 1 • A battery is connected to a bulb and a current of 2mA flows through it. What is the time taken for the battery to deliver 2 C of charge? A. 1 s B. 10 s C. 100s D. 1000s
    24. 24. Quiz 2 • An electric oven has been switched on for 2 hours. Calculate the quantity of electric charges passing through the circuit in this time if the current is 0.5A A. 1C B. 60C C. 360C D. 3600C
    25. 25. Quiz 3 • The electric current supplied by a battery in a digital clock is 0.5mA. a) What is the quantity of charges that flow in half an hour? b) Find the number of charges that flow through the clock? [e=1.6 x 10-19C]
    26. 26. Solution a) Q = It = 0.5 x 10-3 x 0.5 x 60 x 60 = 0.9 C b) Q = ne, where n is the number of electrons and e is the charge of 1 electron. Therefore the number of electrons, n=Q/e = 0.9/1.6 x 10-19 = 5.625 x 10-18
    27. 27. Electric Field • Electric Field is the region where an electric force is experienced Lines of force: Lines of Force are used to represent the direction of an electric field.
    28. 28. Electric Field • . Away from positive charge Towards the Negative charge A positive charge A negative charge As we move closer to the charge, the electric field is stronger The electric field lines neither branch off nor intersect one another.
    29. 29. Electric Field Pattern
    30. 30. Video • nmL853784 • Electric field patterns.mp4
    31. 31. Electric Field Pattern The fields for four important electrode arrangements: 1. Two unlike charges – attraction. 2. Two like charges – repulsion. 3. A charge and an oppositely charged plate. 4. Two oppositely charged plates. (The direction of the arrows shows the way a positive charge would move if placed in the field.) Two similar charges repel each other Two opposite charge attract each other
    32. 32. Effect of Electric Field Acting On A Charged Body
    33. 33. Candle in the electric field • Heat energy from the candle flame produces ionization of air molecules to form positive and negative ions. • Movement of positive ions which are heavier towards the negative plate causes a bigger spread of the flame. • Negative ions which are lighter move towards the positive plate and causing a smaller spread of the flame.
    34. 34. Video • EY3Yv9kC8 • Van De graaf
    35. 35. Van De Graaf generator • Schematic view of a classical Van de Graaff- generator. 1) hollow metal sphere 2) upper electrode 3) upper roller (for example an acrylic glass) 4) side of the belt with positive charges 5) opposite side of the belt with negative charges 6) lower roller (metal) 7) lower electrode (ground) 8) spherical device with negative charges, used to discharge the main sphere 9) spark produced by the difference of potentials
    36. 36. A hair raising experience
    37. 37. Video • 3EK28 • The effect of electric field.mp4 • y1a53k • Flame in electric field.mp4
    38. 38. Summary
    39. 39. Electric Current 1. Made up of the flow of tiny electric charges called electron 2. Static electricity is a build up of these tiny electric charges in one place until the electrical charge is discharged. 3. 3. As an example the ruler rubbed with a clothes, it is charged but static electricity because insulator does not allow flow of the charges. If we use a metal object or a conductor,
    40. 40. Electric Field Lines 1. Always extend from positively charged object to negatively charged object. 2. Positively charged object to infinity. 3. Infinity to negatively charged object. 4. Never cross each other 5. More dense around the objects with the greatest amount of charge.
    41. 41. Try this
    42. 42. Did you get these Solution
    43. 43. EXERCISE Book 1 – section 2.1
    44. 44. Thank You. Geliga Complementing Your Learning
    45. 45. Note: • Thanks to those whose untiring efforts in creating images that made other’s life easier. • The images and contents of the slides are extracts and adapted from various sources/ texts/books. • Send me an email if you discover any error in the contents, or if you want your images removed or if I missed out on crediting your works.