1. Chapter 22 Notes
Current Electricity

2. Section 22.1 Objectives
Describe conditions that create current in an electric circuit.
Use Ohm’s law to calculate properties of an electric circuit.
Differentiate between power and energy in an electric circuit.

3. Electric Current
I=ΔQ/Δt

4. Example Problems
The current in a light bulb is A. How long does it take for a total charge of 1.67 C to pass through the filament of the bulb?
A total charge of 9.0 mC passes through a cross-sectional area of a nichrome wire in 3.5 s. What is the current in the wire?

5. Resistance
R = ΔV/I
Ohm’s law—the resistance is constant over a wide range of applied potential differences

6. Resistors
Can change current by changing the potential difference across the ends of the conductor
I = ΔV/R
How can the current change if the potential difference stays the same?

7. Example Problems
The resistance of a steam iron is 19.0 Ω. What is the current in the iron when it is connected across a potential difference of 120 V?
The current in a microwave oven is 6.25 A. If the resistance of the oven’s circuitry is 17.6 Ω, what is the potential difference across the oven?

8. Sources of Current
Potential difference
Batteries
Generators

9. Section 22.2 Objectives
Explain how electrical energy is converted into thermal energy.
Calculate the amount of power dissipated through resistors.
Calculate the amount of energy used in kilowatt-hours.

10. Electric Power
P = IΔV
Using Ohm’s law (ΔV = IR), we can express the power dissipated by a resistor by the following equations:
P = I ΔV
P = I2R
P = (ΔV)2/R

11. Example Problem
An electric space heater is connected across a 120 V outlet. The heater dissipates 1320 W of power in the form of electromagnetic radiation and heat. Calculate the resistance of the heater.

12. Example Problem
A 6.0 V battery delivers a 0.50 A of current to an electric motor connected across its terminals. What power is delivered to the motor?

13. The Kilowatt-Hour
Amount of electric energy used by a device is its rate of energy consumption (J/s) times the number of seconds (s) used

14. Example Problem How much power does the heater use?
An electric space heater draws 15.0 A from a 120 V source. It is operated, on the average, for 5.0 h each day.
How much power does the heater use?
How much energy in kWh does it consume in 30 days?
At $0.12 per kWh, how much does it cost to operate the heater for 30 days?