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Effects of moving charges

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Presentation on theme: "Effects of moving charges"— Presentation transcript:

1 Effects of moving charges
Electric Current Effects of moving charges

2 Objectives Relate current, potential and resistance using Ohm’s Law.
Determine the power in a current flow.

3 Charges Move in Circuits
Charges travel in a circuit to maintain charge balance

4 Electric Current is Charge Flow
Dq Dt Current = charge flux / time = current Unit: C / s = ampere = A

5 Conductors and Insulators
A conductor is a material through which current flows easily. An insulator is a material through which current does not flow. No material is a perfect insulator or conductor! OK, superconductors do exist.

6 Resistance Hinders Current
Current does not flow unhindered Electrical resistance is akin to friction or drag Expressed as voltage needed to maintain a current, V/A

7 General Physics L12_current
Ohm’s Law I = V R I = current V = voltage = electric potential change R = resistance Good conductors have low resistance. Unit: V / A = ohm (W)

8 Voltage Causes Current
Potential drop is the cause. Current is the effect. Resistance reduces the effect of voltage.

9 Question If you want to increase the current through a resistor, you need to Increase the resistance or voltage. Decrease the resistance or voltage. Increase the resistance or decrease the voltage. Decrease the resistance or increase the voltage.

10 General Physics L12_current
Ohm’s Law Rearranged If you know two, you can find the third. I = V R R = V I V = IR Good conductors have low resistance. I = current V = voltage R = resistance

11 Calculate the Current A 1.5-V battery powers a light bulb with a resistance of 9 W. What is the current through the bulb? Ohm’s Law I = V / R V = 1.5 V; R = 9 W I = (1.5 V ) / (9 V/A) = 1/6 A

12 Board Work A car headlight draws a current of 15 A when connected to a 12-V car battery. What is the resistance of the headlight?

13 Electric Power Formula
General Physics L12_current Electric Power Formula Voltage is work done per charge: V = DE / q Current is charge per time: I = q /Dt So, (voltage times current) = (work per time) = power Good conductors have low resistance. Power = VI

14 Board Work What is the power dissipated by the car headlight drawing 15 A when connected to a 12-V car battery?

15 Another Formula Power = VI Power = I2R
If you know current I and resistance R Ohm’s law tells you V = I R Substitute IR for V in power formula VI = IRI = I2R Power = I2R

16 Yet Another Formula Power = VI Power = V2/R
If you know voltage V and resistance R Ohm’s law tells you I = V /R Substitute V/R for I in power formula VI = V(V/R) = V2/R Power = V2/R

17 Circuit Diagrams Potential source resistor

18 Kirchoff’s Laws Current into any node equals current out of the node
I1 = I2 + I3 0 = I2 + I3 – I1 “Current law” “Junction law” Conservation of charge

19 Kirchoff’s Laws Potential drop around any closed loop is zero
V1 V – V1 – V2 = 0 V1 + V2 = V V “Voltage law” “Loop law” V2 Conservation of energy


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