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PSC 4011

PSC 4011. Electricity: What’s the connection?. PSC 4011: Simple circuits & Ohm’s law . Electric circuit : uninterrupted series of components connected by means of conductors (electrical wires) Simple circuits must contain at least :

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PSC 4011

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  1. PSC 4011 Electricity: What’s the connection?

  2. PSC 4011: Simple circuits& Ohm’s law Electric circuit: uninterrupted series of components connected by means of conductors (electrical wires) Simple circuits must contain at least: _Power supply (provides energy for current to flow) _Conducting wires (allow flow of charge, conduction) _An energy consumption device (impedes the flow of current, E transformation) *By convention current flows from + to – end of battery *For electricity to run, switch must be closed

  3. PSC 4011: Simple circuits& Ohm’s law Conventional symbols

  4. PSC 4011: Simple circuits& Ohm’s law What’s wrong with the diagram?

  5. PSC 4011: Simple circuits& Ohm’s law The Power Supply (a.k.a. Electromotive force of a cell “e.m.f.”) Can be a cell, or a battery (a series of cells). There are different types of batteries (Fig. 2.10, page 2.15): _Regular _Rechargeable (produce less waste) _Alkaline (slowest discharge when stored) See Fig. 2.10, p. 2.15

  6. PSC 4011: Simple circuits& Ohm’s law The Power Supply • A cell is made of two electrodes: anode (negative) & cathode (positive). • Each electrode is made of a different metal, • They are immersed in a solution of an electrolyte.

  7. PSC 4011: Simple circuits& Ohm’s law The three measurable variables in a circuit are: _Potential Difference (Voltage) _Current Intensity _Resistance

  8. PSC 4011: Simple circuits& Ohm’s law Potential difference: Provides the energy transferred between two points in an electrical circuit. This energy is used for the current (flow of electrons) to run through the circuit. • Symbol: V • Unit: Volts (V) • Measured with a device called a VOLTMETER, which must be connected in parallel! (outside the circuit).

  9. PSC 4011: Simple circuits& Ohm’s law Potential difference: • It is measured (parallel) at both ends of the power source (emf) or at both ends of any given resistor or energy consumption device (voltage). • Potential difference along a conductor is considered zero as energy hardly changes as it flows through the wires *energy only changes at power source or energy consumption devices. *V = emf (ε) when measuring V of power source

  10. PSC 4011: Simple circuits& Ohm’s law Current Intensity: Amount of charge that is carried by electrons, per unit of time. ( ) • Symbol: I • Unit: Amperes (A) • Measured with a device called a AMMETER, which must be connected in series! (inside the circuit). • Q: number of charges ( C ) • t: time (s)

  11. PSC 4011: Simple circuits& Ohm’s law Practice: Calculate the amount of charge that flows through a microwave during 5 minutes, if it requires a current intensity of 5.8 A. Q = (I x t ) Q = (5.8 A)(300 s) Q = 1740 C

  12. PSC 4011: Simple circuits& Ohm’s law Multimeter: Measurement instrument that includes an ammeter, a voltmeter and an ohmmeter.

  13. PSC 4011: Simple circuits& Ohm’s law Current Intensity: Ampere-hour (A·h) units correspond to the charge carried by a 1 A current, in one hour Practice: A small remote-control is powered by a 1500 mA·h battery. Calculate the maximum amount of time it can operate without stopping, if the car requires 4.5 A current to function. Q = I t t = Q / I t = 1500 mA·h/ 4.5 A t = 1.5 A·h / 4.5 A t = 0.33 h or 20 minutes

  14. PSC 4011: Simple circuits& Ohm’s law Conductors: Usually metals, they allow the flow of electrons in a circuit (Examples: Silver, Aluminum, Copper) Use: wires in circuits (home, industrial, high tension lines). Resistive conductors: Allow conductivity, but generate lots of heat due to their resistive nature (Examples: Tungsten, Nichrome, Iron, Carbon) Use: light bulb filaments, heating elements Semiconductors: Somewhere between conductors and insulators (Examples: Silicon, Germanium) Use: transistors and diodes in electronics) Insulators: Usually non-metals or materials, because they impede the free flow of charge (electrons) along the circuit (Examples: glass, mica, porcelain, paper, air, rubber) Use: sheathing for electrical wires, insulators high tension cables)

  15. PSC 4011: Simple circuits& Ohm’s law Resistance: Ability of some materials to oppose to the circulation of charges. • Symbol: R • Unit: Ohms (Ω) * Resistors transform electrical energy into other type of energy.

  16. PSC 4011: Simple circuits& Ohm’s law Resistance depends on several factors:

  17. PSC 4011: Simple circuits& Ohm’s law Resistance depends on several factors:

  18. PSC 4011: Simple circuits& Ohm’s law Which is the best conductor? Which the worst? (same material for all) BEST WORST

  19. PSC 4011: Simple circuits& Ohm’s law Ohm’s law: Mathematical relationship between current intensity, potential difference and resistance. or or It states that for a given resistance, the potential difference is directly proportional to the current intensity.

  20. PSC 4011: Simple circuits& Ohm’s law Practice: Given the values of current intensity 30 mA and resistance (40 Ω) for a particular circuit. Calculate the potential difference on each end of the resistance. V = I x R V = (0.03 A) x (40 Ω) V = 1.2 V

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