in series Devices connected in series will have the same amount of charge deposited on each capacitor. But different potential difference. That means

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1 Electric Field Electricity Lecture Series Electric Field: Field an area where any charged object will experience an electric force Kirchoff s Laws The electric field lines around a pair of point charges The electric field lines around a negative point charge pplied Sciences Education esearch Group (SEG) Faculty of pplied Sciences Universiti Teknologi M E jjnita@salam.uitm.edu.my; jjnita@salam.uitm.edu.my; drjjlanita@hotmail.com F on k r 4π r Electric Field Electric Field: Field Place the point charge, at the center of a an imaginary spherical surface of radius r (gaussian surface). The electric field strength is then directly proportional to the surface charge density, amount of charges in suare meter. E F on E 4 πε 0 r 0 0 k Parallel plate capacitors:two metal (conducting) capacitors plates, parallel to each other and separated by non conductors such as air, paper, plastic etc. Use to store charges and hence store electrical energy. 0 0r Experiments found that mount of charges deposited on plates when connected to a battery is proportional to the potential difference applied across plates. ; C But the surface area of a sphere is 4πr E Coulombs olts Where C is the capacitance C of the capacitor. σ 4π r ε 0 ε0 ε0 n addition, the E field depends on the battery and the plate separation 4 Devices connected in parallel will have the same potential difference. But different current flowing. That means different amount of charges through each circuit. W B 0 Work must be done by the The work done is then stored as battery to move charges electrical potential energy. to the plates. s more charges are deposited, W C C the potential difference across the plates also W C E d κε 0 increase. More work has d to be done. d in parallel Work done is related to the electric potential. t any point, electrical potential is the work done by electric force to move a positive test charge from to B E or Farad Energy stored in capacitors Since C, then T (C C) T. Hence, C C 5 6

2 in series Devices connected in series will have the same amount of charge deposited on each capacitor. But different potential difference. That means different T Electric circuits Since /C, then T ( T C C ) C C Hence C C C C 7 Electric Charges Electric Charges Learning Outcome: Learning Outcome:. Explain and relate between batteries, electromotive force, electrical potential and electrical potential energy. 6. State Kirchoff s Junction ule for current and Loop rule for potential difference.. State Ohm s Law and apply it to resistors connected in a circuit. 7. Solve for variables such as currents and potential differences in circuits by using Ohm s Law and or Kirchoff s Laws. Obtain, using Ohm s Law, total resistance connected in series. 8. Evaluate circuits for current flowing and related variables using current loops. 4. Obtain, using Ohm s Law, total resistance connected in parallel. 5. Discuss the significance of internal resistance. 9 0 Electromotive force: force maximum potential difference existing between terminals of batteries. Symbol used is. n addition, note that the potential at a point is the electrical potential energy for each coulomb of charge Electromotive force: force maximum potential difference existing between terminals of batteries. Symbol used is. Current flow, E field Free electrons flowing n the wire The car battery with electromotive force of The car battery with electromotive force of ; joules of energy for each coulomb of charge carrier The dry cell with electromotive force of.5 Symbol for a battery and directions of current flow and flow of free electrons

3 esistive Elements: Elements Electromotive force: force maximum potential difference existing between terminals of batteries. Symbol used is. Surface, Surface, ρ resistance is property of object; resistivity is property of material Current flow, E field Free electrons flowing n the wire mpere is the amount of charge in coulomb that passes through a across sectional area in one second t resistance is property of object; resistivity is property of material esistive Elements: Elements Symbol for a battery and directions of current flow and flow of free electrons 4 esistive Elements: Elements ρ resistance is property of object; resistivity is property of material ; ; Surface, Surface, Surface, 5 ; esistive Elements: Elements Ohm s Law: current flowing through a circuit is directly proportional to the potential difference or applied voltage, or /. ρ ; EPE t Power is the resistance of the resistor (property of object), ρ is the resistivity which is a constant for a given material (property of material) t E field, & One ohm of resistance means a potential difference of one volt for each ampere of current flow 6 esistive Elements: Elements Ohm s Law: current flowing through a circuit is directly proportional to the potential difference or applied voltage, or /. Surface, Electrons flow Device 7 8

4 Series Wiring: the same amount of current passes through each device in the circuit whereas the potential differences through each device may be different but the sum be eual to the EMF,. Series Wiring: the same amount of current passes through each device in the circuit whereas the potential differences through each device may be different but the sum be eual to the EMF,... N N ( ) s N.. N N.. N N eual (.. N ) s S.. N and N For capacitors, and.. N S.. N 6 Ω Ω 9 Ω C 9 Parallel Wiring: the same amount of potential difference across each device but different current passes thru each circuit,. Parallel Wiring: the same amount of potential difference across each device but different current passes thru each circuit,..... N N 0 eual N eual.. N.. N N.. p N Parallel Wiring: the same amount of potential difference across each device but different current passes thru each circuit,. Series & Parallel Wiring:.. N eual Parallel resistors: Series resistors: Since,.. p N 4Ω 8Ω 8Ω Hence, p 8 Ω eual eual eual Series resistors: 4 4

5 nternal resistance: batteries and generators add to the circuit s total resistance since each them have internal resistance inside the device itself. Caused by ageing and corrosion. Do example. Kirchoff s ule: Law : Junction ule. Sum of current into a junction is eual to sum of current leaving the junction. in out ule : Loop ule. round any closed circuit loop, the potential drops must eual potential rise. eual drop rise r (r ) 5 6 Kirchoff s ule: ule : Loop ule. round any closed circuit loop, the potential drops must eual potential rise. Solving circuit problems using Kirchoff s rules: Choose current direction. Can be any direction. f our final answer is negative, then we had chosen the wrong direction. Does not affect our solution Label resistors plus and minus. Current flows from high (positive) to low potential (negative). pply junction rule. pply loop rule. Choose either clockwise or counterclockwise direction and write the potential drops and potential rise. Choose as shown: drop Start from : use loop rule CW rise 6 4 ( Ω) 6 (8 Ω) 4 (0 Ω) / 0 Ω B H Start at B Start at B B H Start from B, go CW Loop: BEF (0. Ω )(0.0 Ω)B 4 Start from B, go CW Loop: BCDE (.0 Ω)H(0.0 Ω )B 9 0 5

6 B H ().. B (5) (0. Ω ) (0.0 Ω) B 4 () 0. (.0 Ω)H(0.0 Ω )B () emove from euation. Multiply (6) by Substitute (). into (). B 0. 0 B. ewrite () emove from euation. Multiply (6) by. B B. (5) 0. B 4. B Finally, in Start from : Loop : C Loop Loop : D Then: (/) Loop F Solve: ( ) E Solve: () Kirchoff s ule: ule : Loop ule. Using loop currents instead of just current branches. So, no need junction rule. E Then / (/) Loop () (/) D F Solve: ( ) Loop C 4 Then: (/) Start from : Loop : Loop : 4 Kirchoff s ule: ule : Loop ule. round any closed circuit loop, the potential drops must eual potential rise. B.9 rise Then using junction rule: drop B n: & ; Out:. 9 Then using junction rule: H Kirchoff s ule: ule : Loop ule. round any closed circuit loop, the potential drops must eual potential rise. n:; Out: & out (8) Kirchoff s ule: Law : Junction ule. Sum of current into a junction is eual to sum of current leaving the junction. (7) B 9. 0 Substitute into (7) (7) (6) (7) (5) (6) 0. B 4. (4) 0. 0 B Then: ( )/ Ω, Ω, Ω, 44 Ω,,,

7 Kirchoff s ule: ule : Loop ule. Using loop currents instead of just current branches. So, no need junction rule. Loop () Loop 4 Loop () Loop ( /) ( / ) (4) Loop 9 ( / ) (/) (5) Loop 7 ( 4 / ) ( / 7 ) (6) Ω, Ω, Ω, 4 4 Ω,,, 7 () 7 7

Capacitance. A different kind of capacitor: Work must be done to charge a capacitor. Capacitors in circuits. Capacitor connected to a battery

Capacitance. A different kind of capacitor: Work must be done to charge a capacitor. Capacitors in circuits. Capacitor connected to a battery Capacitance The ratio C = Q/V is a conductor s self capacitance Units of capacitance: Coulomb/Volt = Farad A capacitor is made of two conductors with equal but opposite charge Capacitance depends on shape