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# 2.1 electricity

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### 2.1 electricity

1. 1. 1 PHYSICS MODULE 2. ELECTRICITY
2. 2. TOPIC: 2 ELECTRICITY 2.1 ANALYSING ELECTRIC FIELD AND CHARGE FLOW CONTENTS: 1. CHAPTER HIGHLIGHT (30 MINUTES) 2. ACTIVITY (50 MINUTES) 2
3. 3. 3. ASSESSMENT (40 MINUTES) 4. MARKING SCHEME(ANSWER KEY) CHAPTER 2 ELECTRICITY 2.1 Analysing electric fields and charge flow 1. _____________________can be produced by rubbing an object (e.g. polytena rod) with soft fabric. 2. The produced charge is static which is known as _____________________. 3. Symbol for the quantity and unit of electric charge. Symbol for the quantity Symbol for the unit of electric charge of electric charge, Coulomb 4. Type, symbol and value of a unit of electric charge Type of charge Symbol Value of a unit ( Coulomb) Positive charge (proton) Negative charge (electron) 5. The relationship between the total of electric charge and the amount of electric charge. 3 Q = 1 C
4. 4. The total of The amount of The value of a unit electric charge electric charge of electric charge ( +1.6 x 10-19 C ) 6. Example: What is the amount of the electron needed to carry charge of 1 C ? Formulae: Q = ne Given: Q = 1 C Find: n = ? e = +1.6 x 10-19 C Solution: Q = ne .’. n = Q e = 1 1.6 x 10-19 = 6.25 x 1018 electrons 7. Electric current is defined as the rate of ___________________. 8. Example: If the current which flows through a bulb within a minute is 1.5 A. Calculate the electric charge that has flowed within a minute. Formulae: Q = It Given: I = 1.5 A Find: Q = ? t = 1 minute = 60 s Solution: Q = It = (1.5)(60) = 90.0 C 4 Q = ne Current = Rate of charge flow i.e. Current = Charge flow Time Formulae: I = Q » Q = It t Unit: A = Cs-1 » C = As
5. 5. 9. The relationship between the current flow and the electric charges. The above set up designed to show that the electric charges which flow through a conductor produce electric current. 10. An electric field is an area which if entered by a charged object, it will experience the __________________ which is produced by a quantity of charge. 11. The paths of electric field of a positive charge can be represented by the electric force lines or electric field lines. 12. The characteristics of the electric field line are: (i) The lines begin from the positive charge and end at the negative charge. (ii) The lines do not overlap. (iii) The lines repel each other. (iv) The lines intensity represents the electric field intensity. 13. The pattern of electric field lines depends on the pattern of charged object. (a) single spherical (positive charge) (b) single spherical (negative charge) 5 galvanometer Van de Graaff generator Water tap +-
6. 6. (c) two spherical of same charges (d) two spherical of different charges X = neutral point (e) a positive spherical & a negative plat (f) two plats of different charges 14. The effect of the electric field upon the charges. (i) A ping-pong ball coated with conducting material Step Observation Explanation (1) A Very High Voltage source is connected to the plats F1 F2 • Attraction force on the ping-pong ball from positive plat is at the magnitude with the attraction force from negative plat, 6 - -0+ -0 + X - + - + -
7. 7. The ping-pong ball remains motionless i.e. F1 = F2. • The ping-pong ball is neutral (2) The ping-pong ball is pulled until it touches negative plat F (i) • When the ping-pong ball touches the negative plat, this ball will receive the electrons and will be charged negative. • This negatively charged ball will be pushed by the negative plat and will be attracted by the positive plat F (ii) The ping-pong ball oscillates back and forth between the two plats until the Very High Voltage source is disconnected • Once the ping-pong ball touches the positive plat, all of its negative charges will be neutralized. • Further, the ball will be positively charged • This positively charged ball will be pushed by the positive plat and will be attracted by the negative plat • The ball later will touch the negative plat, and the processes will be repeated. (ii) A candle flame Step Observation Explanation A Very High Voltage source is connected to the • The heat energy produces positive and negative ions 7 - - - - -+ + + + + -+ - + + +
8. 8. plats The flame is not symmetrically distributed The flame is deflected more towards the negative plat around the candle flame • Positive ions which are heavier will bring more flame attracted towards the negative plat. This happens because the positive ions move rather slow • Negative ions (electron) which are lighter will occupy smaller flame area Assessments Objective Questions 1. If a charge of 300 C flows through a bulb every 2 minutes. Calculate the current which flows through that bulb. A 2.0 A B 2.5 A C 150 A D 600 A 2. There are 5 x 1018 electrons flow through a bulb within 20 seconds. What is the value of current flow ? ( Given e= 1.6 x 10-19 C ) A 40 mA B 0.8 A C 16 A D 80 A Structure Questions A. 1 Define the following terms. (a) Electric current: __________________________________________________ __________________________________________________ 8 + - Electric current is defined as the rate of charge flow.
9. 9. (b) Electric field: __________________________________________________ __________________________________________________ 2 Sketch the electric field lines showing the direction of the field. (a) single spherical (positive charge) (b) single spherical (negative charge) (c) two spherical of same charges (d) two spherical of different charges 9 - -0+ -0 +- An electric field is an area which if entered by a charged object, it will experience the electric force which is produced by a quantity of charge.
10. 10. (e) a positive spherical & a negative plat (f) two plats of different charges B. 1 Explain the effect of the electric field upon the charges in the following cases: (i) A ping-pong ball coated with conducting material (ii) A candle flame 10 Answer: 1 B 2 A + - + -
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