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Electric Circuit

Electric Circuit. Charges in Motion OCHS Physics Ms. Henry. Current. Amount of charge per time that passes through an area perpendicular to the flow: 1 ampere = 1 coulomb/second A coulomb is a unit of electric charge: 6.241x10 18 electrons. I (A) = ∆q (C) ∆t (s).

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Electric Circuit

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  1. Electric Circuit Charges in Motion OCHS Physics Ms. Henry

  2. Current • Amount of charge per time that passes through an area perpendicular to the flow: • 1 ampere = 1 coulomb/second • A coulomb is a unit of electric charge: 6.241x1018 electrons I (A) = ∆q (C) ∆t (s)

  3. Resistance • We know that current is proportional to voltage for conductors. • Resistance is the proportionality constant within the circuit (what causes a variation). • The relationship is called: Ohm’s Law • 1 Ohm (Ω)=1Volt/1 Ampere V(Voltage)=I(Current)R (Resistance) (Volt, V) = (Amp, A) (Ohm, Ω)

  4. Resistivity • Resistance depends upon a conductor’s length (l), it’s cross-sectional area (A), and it’s resistivity (ρ). • Resistance to current happens when the flow of moving charges is hindered by the material of the wire. • Thus, • Unit: ohm-meter. R =lρ A Note: A resistor is specifically designed to resist current in a circuit. For example: a light bulb or heating element.

  5. Voltage • Provided by the battery between it’s terminals. • A constant potential difference comes from the battery - for example, 6 Volts. • When current passes through the light bulb, charges move from a higher potential to a lower, with a difference of 6 volts. • Energy is then being converted into light or heat. • Often represented by: ε

  6. The electric field set up in the wire causes the current to flow; which happens when the circuit is complete. • Current flows toward the positive charges; from the negative end of the battery to the positive.

  7. Electrical Power & Energy • Power (Watts): rate of energy usage. • 1 watt = 1 Joule/second = 1 ampere-volt + ε + ε P = IV = V2 = I2R R

  8. Direct Current (DC) CircuitDirect current means current flowing in only one direction. Series Parallel Current branches off at the intersection point; part of the current goes one way part of the current goes the other. The potential drop of current is the same regardless of which path is taken; thus, the voltage difference is the same over either resistor. (Vbatt=V1=V2) Currents sum to the total current: • Current is the same at any point in the circuit. (I = I1=I2) • The potential difference supplied by the battery equals the potential drop over R1 and the potential drop over R2. Thus, V=V1+V2 Ohm’s Law V=IR1+IR2 V=I(R1+R2) Equivalent Resistor Req= R1+R2 I=I1+I2 I= V + V  I=V( 1 + 1) 1 = 1 + 1 R1 R2 R1 R2 Req R1 R2

  9. Kirchhoff’s Rules • Junction Rule: The sum of the currents entering the junction must equal the sum of the currents leaving the junction; referring to the conservation of charge. • Conservation of Energy: the charge moving around any loop must gain as much energy from batteries as it loses when going through resistors. When applying the rules: Use consistent sign conventions. (i.e. counterclockwise or clockwise) If you choose an incorrect direction initially the solution will have a negative current.

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