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Conservation of charge and energy

Conservation of charge and energy. (c) recall Kirchhoff’s first law and appreciate the link to conservation of charge (d) recall Kirchhoff’s second law and appreciate the link to conservation of Energy. Kirchoff`s 1st law.

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Conservation of charge and energy

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  1. Conservation of charge and energy • (c) recall Kirchhoff’s first law and appreciate the link to conservation of charge • (d) recall Kirchhoff’s second law and appreciate the link to conservation of Energy

  2. Kirchoff`s 1st law • Sum of currentsflowinginto a pointisequaltothesum of currentsflowingout of thatpoint

  3. Conservation of charge • Chargecannotbecreatedordestroyed…. • So current (charge per unit time) into a junction…. • Mustequalthecharge per unit time flowingout.

  4. Use it….. • Whenanalysingparrallelcircuits

  5. Kirchoff`s2nd law • Aroundanyclosedloopthesum of emfsisequaltothesum of p.d.s.

  6. Emfs and p.d.s. • Whatisthedefinition of emf? • OrEnergytranferred (fromotherforms)/Chargepassinground complete circuit. • And p.d. • Electricalpotentialenergytranferred (tootherforms)/Chargepassingbetweentwopoints.

  7. Conservation of energy • Sincethestartpoint and endpoint are thesametheymusthavethesameenergy. • So thesecondlawsays “each coulomb of chargedissipatesalltheenergy(p.d.s) thatitgains (emfs) as itgoesaround a complete circuit.

  8. Practise • These can get quite trickyparticularlywhenthereis more thanoneemf in a parallelcircuit. • Problems are oftencombinedwith ideas of internalresistance and power.

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