1. Applied Physics and Chemistry Circuits Lecture 1
Current Electricity
Applied Physics and Chemistry Circuits Lecture 1

2. Electric Current Current is flow of charges
There must be a complete loop (closed) for flow to occur
Flow from high potential to low potential
As potential decreases, work is done by charges
Conventional current is flow of positive charges
Do positive charges actually flow?

3. Electric Current Current may be direct or alternating
Direct current: flows in one direction
Alternating current: flows back and forth

4. Electric Circuit Required for current electricity
Closed loop or conducting path from high to low potential
Must have four parts:
Source of charges (area of high potential)
Path for charges
Device that reduces potential energy
Sink (area of low potential)

5. Electric Circuit Energy is conserved in the circuit
Charge is conserved in the circuit
Energy carried by current depends on charge and potential difference
ΔE = qV
Remember, V is the potential difference
1 V = 1 J/C

6. Electric Current Current is rate of flow of electric charge
Measured in Coulombs / sec
1 C/s = 1 A (Ampere)
Symbol for current is I

7. Electric Power
Rate of energy transfer
Measured in Watts
1W = 1 J/s

8. Electric Power Since P = E/t And E = qV And q= It Then P = VI
Power is current times the potential difference.

9. Equation for Amber
In a circle! p i v

10. Electric Power
If the current through a motor is 3 A and the potential difference is 120 V, what is the power of the motor?
Known: I=3A V=120 V
Equation: P=IV
P=(3A)(120V)=360 W

11. Electric Power Problem 2
A 6 V battery delivers 0.5 A of current to an electric motor. What is the power rating of this motor? What we know: V = 6V I = 0.5 A Equation: P = IV Substitute: P = (0.5 A)(6 V) Solve! P = 3 W

12. Electric Power Problem 2 Contd.
How much energy does the motor use in 5.0 minutes?
What we know:
P = 3 W t = 5.0 min = 300 s
Equation:
P = W/t which means P = E/t and E = Pt
Substitute:
E = (3 W)(300 s)
Solve!
E = 300 J