# Current & Resistance

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1. current
rate at which charges move through cross section of wire or given medium; movement of electric charge
2. SI unit for current
1 ampere A = 1 coulomb/sec c/s
3. charge carriers
positive or negative charges in motion
4. conventional current
• current consisting of positive charges that goes in direction of electric field, from positive to negative
• represents the effect of the actual motion of the charge carriers (equivalent conventional current of negative is in opposite direction; same direction for positive)
5. drift velocity
net velocity of the charge carrier moving in an electric field, taking all of their collisions and zig zags into account
6. how a current is created
• potential difference is applied across conductor
• charge carriers have to be "pumped" through the circuit; work has to be done on them to maintain v
• electric field force sets the electrons in movement
• charges collide with atoms in the device and convert electrical potential energy to kinetic energy to move
7. how batteries/generators maintain a potential difference
they convert energy into electrical energy, this energy is supplied to charge carriers
8. energy conversion in batteries vs. generators
• batteries convert chemical energy to electrical energy
• generators convert mechanical energy to electrical energy
9. direct current
• charges move only in one direction, potential difference is fixed
• generated by batteries and generators
10. alternating current
• terminals of the source of the electrical potential are always changing signs, no net motion
• only generated by generators
11. point of conductor
surface perpendicular to the motion of the charges
12. circuit
charge flows through a closed path and returns to its starting point
13. power
rate at which work is done; rate of energy transfer
14. power of a resistor
amount of heat produced when current flows through (joule heating: heating of the resistor)
15. electromotive force emf
max potential difference of a device
16. terminal voltage
• actual potential difference between the terminals
• less than the emf because of the internal resistance of the battery (caused by collisions between charges and atoms within battery)
17. resistance
opposition of the motion of charge through a conductor, quantified by the geometric characteristics of the material through which the charge is moving
18. resistance SI unit
1 ohm = 1v/amp
19. resisitivity and temperature relationship
• usually resistivity and temperature increase together
• for semi-conductors, there is an inverse relationship
20. Ohm's Law
• ratio of a potential difference applied across a conductor to the current through the conductor is constant
• graph of current vs. potential difference is linear with a constant slope equal to the inverse of the resistance
21. ohmic
materials that follow Ohm's Law; constant resistance over a wide range of potential differences
22. potential difference and current relationship
• higher potential difference means greater current
• directly related
23. length effect on resistance
shorter objects have less resistance; longer objects have greater resistance
24. cross-sectional area effect on resistance
greater area has less resistance; smaller area has greater resistance
25. temperature effect on resistance
lower temperatures have less resistance; higher temperatures have more resistance
26. relationship between current and resistance with constant potential difference
inverse relationship; current decreases when resistance increases
27. short circuit
• has very little resistance so more energy gets dissipated, lacks a resistor
• usually the circuit is cut off from a capacitator so recharging does not occur; burns out quickly
• low resistance increases current, can cause circuit to overheat and catch fire
28. series circuit
provide a single conducting path without junction; only one path for the charge to follow
29. parallel circuit
connected with junctions providing separate conducting paths; some charged go one way, others go the other
30. schematic diagram
graphic representation of an electric circuit with symbols representing circuit components
31. electric circuit
path through which charges can be conducted; set of electrical components connected so that they provide complete paths for charge movements
element that dissipates energy, increases the resistance and is a type of resistor (e.g. light bulb)
33. simple circuit
has a source of potential difference and electrical energy (e.g. battery) and a load (e.g. light bulb)
34. closed circuit
closed-loop path for electrons to follow, path from one battery terminal to the other is complete, switch is closed to allow steady current flow
35. open circuit
incomplete path and no charge flow and no current, switch is open, circuit does not work
36. potential difference across a load and terminal voltage
• potential difference across a load equals the terminal voltage
• conservation of energy says that the energy gained must equal the energy dissipated in a charge's trip in a circuit
37. watt conversion
1 w= 1 vxa
38. battery drawing
---| |--- longer side is positive, shorter side is negative
39. relationship between parallel and series circuit
inversely proportional
40. equivalent resistance
• a single resistor can replace a group of series or parallel resistors; represents total current found by using individual resistance values
• for series circuits, add the sum of the individual resistances
• for parallel circuits, do the same with inverses
41. current in series/parallel circuits
• constant throughout series circuits (conservation of charge, current is the same throughout all resistors)
• proportioned across each resistor in parallel circuits
42. voltage in series/parallel circuits
• proportioned across each resistor in series circuit
• constant throughout each resistor in parallel circuits (sides of bulbs are connected to common points, so voltage across is the same)
43. do series/parallel circuits require all elements to conduct?
• series require all elements to conduct
• parallel do not require all elements to conduct; provides separate alternate pathways
44. relationship between equivalent resistance and individual resistances in parallel circuits
inversely related; low equivalent resistance can be created with a group of high resistances in parallel
45. complex circuits
consist of series and parallel circuits
 Author: Gymnastxoxo17 ID: 276443 Card Set: Current & Resistance Updated: 2014-06-15 17:36:33 Tags: Chapter Nineteen Twenty Folders: H Physics Description: , Show Answers: