1. Review of Calculations

5. Resistance text 10.4 pgs. 315- 319 circuit symbol
Resistors slow down (resist) the flow of electric current
We use resistors to change electrical energy into other forms of energy
Toaster →
Light bulbs →
Fan →

6. The same voltage does not always produce the same current because the resistance in the circuit affects current flow.

7. In 1827 George Ohm discovered the ratio of voltage to current was constant for a given conductor. He called this the resistance (R) of the conductor! R (Ohms) = Voltage (Volts) Ω I (Amps)

8. R = Voltage (Volts) (Ohms) Ω I (Amps) What resistance does a light have if the voltage is 4 volts and a current of .02 Amps is measured?

9. R = V V = I x R I = V I R What voltage is in a circuit with an 80 Ohm resistor and a current of 50 mA? What current would be in a circuit with a 6 volt battery and a 125 Ω resistor?

10. Ohm’s Law.
A linear graphical relationship exists between voltage and current for a resistor in a circuit
This ratio is equal to the resistance
You can measure resistance and voltage and graph them to find this relationship (from the slope)

11. For every increase in voltage there is an increase in current

12. Try This: What is the resistance shown by this graph of voltage vs
Try This: What is the resistance shown by this graph of voltage vs. current?
Voltage (V)
Current (Amps)

13. (for n identical resistors)
SUMMARY for CIRCUITS
Type of Circuit
Series Circuit
Parallel Circuit
Total Current (IT)
IT = I1 = I2 = I3
IT = I1 + I2 + I3
Total Voltage (VT)
VT = V1 + V2 + V3
VT = V1 = V2 = V3
Total Resistance (RT)
RT = R1 + R2 + R3
RT = R/n
(for n identical resistors)