14 Current of Electricity Notes

\kK ©¥©¥ h m n c fi w ©¥\ k in ©¥lh ; lbldd ton * w L \ ūr on the term ina©¥ potentia©¥ difference and output pow er. (k) show an understanding of the effects of the intem a©¥ resistance of a source of e. m . f. energy considerations. ü) distinguish between electrom otive force (e. m . f. ) and potentia©¥ dilference (p . d. ) using «i) reca©¥©¥ and so©¥ve prob©¥em s using R - p l / A . (h) sketch the resistance - tem perature characteń stic of an N T C therm istor. coefficient (N T C » therm istor. ohm ic resistor, a s e m ic o n d u c to r d io d e , a fila m e n t ©¥am p and a negative tem perature f9) sketch and exp©¥ain the 1 - V characteristics of vań ous e©¥ectrical com ponents such as an (f) reca©¥©¥ and sobe prob©¥em s using the equation V ¡¤ I R . (e) reca©¥©¥ and so©¥ve prob©¥em s using the equation P . ©¥V , P - I Z R a n d P ¡¤ V Z / R . (d) recall and sobe problem s using the equation V - W / Q . (c) recall and so©¥ve problem s using the equation Q = l t . the num ber density of charge carriers and V is the drift vekxtity . (b) derive and use the ¢æ q uaüon I = n A v g fo r a c u ©¥T e n tm rry in g c o n d u c to r, w h e re n l8 (a) show an understanding that electric current ©¥s the rate of f©¥ow of charge , C andidates shou©¥d be ab©¥e to outcom es Learning e S o u r ces of e©¥ect rom o t ©¥ve for ce R e a l atan c e an d re©¥©¥©¥dv ©¥ty P o t en t ©¥a©¥ D ©¥ffer en c e C ontent . E lectr©¥c C u rre n t 1 4 C uR R E N T oF E L E C T R ©¥c 国 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

unit tim e. average electr©¥c current ©¥©¥*©¥ ©¥s equal to the net charges that pass thro ugh the a rea per If aQ ls the am ount of charge passing through this surface in a tim e interval A t, the Ù³ ー «ß«Î«Ë 4 í» . below . (This area A cou©¥d be the cross sectional area of a w ire, fo r e x a m p le . ) S uppose charges are m oving pe ñé endicular to a surface of area A as show n in the figure P a g e P age 2 of 2 4 İ = ©¥ j ' ©¥ ' at dr (2) as the di¨¤erential lim it of average current. If the rate at w hich charges flow varies w ith tim e, the ©¥nstantaneous current 1 is defined ©©ili¨¤ LL " " m rm M is defined as the tate of f©¥ow of cte and ©¥ts U nit current ©¥ E lectric W nenever charged particles m ove, a n e le c tr ic c u rr e n t is said to exist. 1 4 . 2 E ©¥ectric C urrent 1 & C harge a electricn©¥ circuit. term inal. T o ana©¥yse sucH a c©¥osed circuit, w e s hall now ©¥ook at thę different parts of the r source of e. m . f. To one or m ore devices, lik e a re s is to r, a n d then back to the other provided by the connecting w ires, for electrical charges to flow nom one term inal of the T he figure above shows a closed electrica©¥ circuit. T here is a continuous conducting path, C onductor of resistance R C ircuit ©¥ E ©¥ectrica©¥ 1 4 . 1 ©¥ntroduction pH Y S ©¥C S D E P A R T M E N T R A F F L E S ©¥N S T IT U T ©¥O N