13 Electric Field Notes

P a g e 1 of 2 5 concepts in the gravitational field and in the electrical field topics. conservation law as w ell. T here are im portant analogies and distinctions betw een experience forces in electric and m agnetic fields. Like m ass - e n e r gy, charge obeys a m ass experiences a force in a gravitational field, a n d electrically - c harged objects seem s to be precisely quantised, w hile it is not clear if m ass is quantised . A n object w ith an attribute that appears to be just as fundam ental as m ass, o r e v e n m o re s o - c harge E lectrom agnetic interactions involve particles that have a property called electric charge, gravitational and electrom agnetic interactions. T opics sub - a tom ic level, a large num ber of daily hum an experiences can be explained by S ect©¥ons and and weak interactions. W hile the strong and weak interactions explain phenom ena at the L inks B etw een T here are four fundam ental forces in physics : the gravitational, e lectrom agnetic, s tro ng * ee space or air. (k) use the equation V - Q /4 ¨¡￡o' fo r the e le ctric pote ntia ©¥ in the fie ©¥d of a po int ch arg e in potential gradient at that point. ü) state that the field strength of the electric field at a point is num erica©¥ly equal to the bringing a sm all test charge from infinity to that point. «i) define electric potential at a point as the w ork done per unit positive charge in (h) describe the effect of a uniform electric field on the m otion of charged particles. (g) ca©¥cu©¥ate the forces on charges in uniform e©¥ectric fields. plates in term s of potential difference and plate separation. (f) calculate the e©¥ectric field strength of the uniform field betw een charged parallel space or air. (e) recall and use E - Ql4of 2 for the e lectric fie ld strength of a point cha rg e in free between tw o point charges in free space or air. (d) recall and use coulom b ' s law in the form F = Q q/4mof 2 for the e©¥ectric force ©­ 叼 electric field and gravitational field. (c) recognise the analogy betw een certain qualitative and quantitative aspects of (b) represent an electric field by m eans of field lines. positive charge placed at that point, force and define electric fie©¥d strength at a point as the electric force exerted per unit O utcom es (a) show an understanding of the concept of an e©¥ectric field as an exam p©¥e of a field of L earning C andidates should be ab©¥e to E lectric potentla©¥ tl ? (: n t t ©©& . . . L , J I k ) U niform electric fields 3 k u , $ E ©¥ectric f©¥eld of a point charge cT I T t \ E lectric force bew een po©¥nt charges /. . N v t \ t r C ontent C oncept of an e©¥ectric neld éÈ 团 团 1 3 e E C T R ©¥C F ©¥E L D 碘 嚇 i õ¹国fiį i

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P a g e 2 of 2 5 of energy conservation Lenz ' s law as circuits of energy in . c o nse rv atio n circuits of charges in conservation ' " ti. . infinitely extended planes external B - field charges, n e gligible internal resistance, charge and an . S im p lify ing a ssu m ptio n s : e . g . point betw een a m oving patterns, e tcinteraction equipotential lines, m a gnetic flux density F ©¬ as the e lectric circuits, field lines and field ¡¤ C o m m o n re p re se n ta tio n s : d ia g ra m s o f and an external E - . F araday ' s law betw een a charge interaction . O h m ' s law (for ohm ic conductors) F E as the ¡¤ M i cros cop i c mo d e l of the f©¥ow of cha r ge s ©¥deas ©¥nteractions L inks to C ore S ystem s and M odels and R epresentations excitation, from nerve im pulses that spread through specia©¥ tissue in the heart m uscles. signalling and control. T he heart rhythm s are m aintained by w aves of electrica©¥ arise from electrica©¥ forces at the atom ic leve©¥. In biology, e ©¥ectricity is also im portant in E ven m ore fundam ental©¥y, e la stic forces in springs and contact forces between surfaces m agnetism in solid state m aterials. Innovations are also pushing on the quantum frontier. sm artphones are the product of our deep understanding of the physics of e©¥ectń city and alternating current and voltage transform ers. S eniiconductor devices in com puters and T ransm itting electrical energy over ©©ong distances is m ade feasible by the use of to D aily L ife force and current produced by a changing m agnetic flux or a tim e - v a r ying m agnetic field. and R elevance C onverting energy into electrical energy traditiona©¥©¥y involves the induced electrom otive A pplications T echnologies harnessing electrical and m agnetic properties pervade m odern society . phenom ena contributed to the developm ent of the theory of relativity . in this m agnetic field experiences a force. T his apparent asym m etry in e©¥ectrom agnetic M oving charges produce a m agnetic field, a n d another m oving charge or current placed charges w hether m oving or stationary, m a gnetic forces act only on m oving charges. by M axw e©¥l ' s law s of eïectrom agnetism . U nlike electric forces, w h ic h a c t o n e ©¥ectric T oday, w e u n derstand m agnetism as an e« ect inseparable from e©¥ectricity, s u m m a rised T he m ystery of m agnetism w as first discovered ©¥n m agnetic stones by the ancients. ñé conservation provide pow erfu©¥ tools to analyse a variety of electrical circuits. can be experim entally m easured. A pp©¥ying the principles of charge and energy by potentia©¥ differences (a©¥so known as voltages) . B oth current and potential di¨¤erence m ostly su¨¤ices. T he collective m ovem ent of charges results In e©¥ectrical current, driven result in a m acroscopic description where consideration of energy and electric potentia©¥s a circuit, the com plicated enects of forces and electric fie©¥ds at the m icroscopic level provide a m eans of conveying energy and Inform ation from one p©¥ace to another. W ithin P ractical use of e©¥ectricity often occurs ©¥n clrculte rather than ©¥n free B pace. C ircuits as with gravitationa©¥ potential and gravitational potential energy . s©¥tuation. T erm e like electric potential and electric potential energy are defined sim ilarly route to so©¥vlng problem a that can in certain cases bring out the sim plicity of the energy in the context of e©¥ectrlca©¥ Interactions as w ell, a n d these ideas provide another ©¥aw of gravitation for ©¥so©¥ated point m asses. W e can uee the concepts of w ork done and point charges ia governed by C ou©¥om b ' a law , w hich ia m athem atically sim ilar to N ew ton ' s in this fie©¥d experiences a force due to thls neld. T he e©¥ectric force between two isolated A charge produces an electric field In the space around ©©t, a n d a second charge placed P H Y S ©¥C S D E P A R T M E N T R A F F L E S IN S T ©¥T U T ©¥O N

P a g e 3 of 2 5 tow ards Q or to the left. S ince both charges are opposite©¥y charged, the force acting on q due , to Q is directed (b) M agnitude of force, or to the right. S ince both charges are positive, the force acting on g due to Q is directed aw ay ūom Q 4 nf o r z \ T Ĺr ©©lH o ' ' ) ©¥. o \ \ n- 3 S olution (a) M agnitude of force, m agnitude and direction of the force on q by Q . (b) If q is negatively charged instead, but w ith the sam e m agnitude, determ ine the (a) D eterm ine the m agnitude and direction of the force acting on g by Q . 3 . 0 m Q ¡¤ ¡¤ 9 E xam p©¥e 1 T w o charges Q (+ 2 . 0 pc) and 9 (+ 1 . 0 pc) are separated by a distance of 3 , 0 m . and negative. Like charges repel, w hi©¥e unlike charges attract. attractive or repulsive. T his is because there are tw o types of charges - positive force is that the form er is alw ays an attractive force while the latter can be * T h e m ajor di¨¤erence between gravitationa©¥ force and electr©¥c (or electrootatïc) inverse - s quare law s. w o re - U om coulom os ' law ana N ewton - S ©¥aw or gravnaï ©¥un aru au©¥ne\©¥©¥ï ©¥ea ©¥e ©¥e©¥©¥eu w aa N ote