Chapter 20. Foundations of Physics. Electricity and Magnetism. Electric Circuits and Power. 20 Series and Parallel Circuits 20 Analysis of Circuits 20 Electric Power, AC, and DC Electricity. Objectives. Recognize and sketch examples of series and parallel circuits.
Foundations of Physics
Electric Circuits and Power
a. Batteryf. Fixed resistor
b. Light bulbg. Capacitor
c. Motorh. Buzzer
d. Switchi. Ammeter
e. Variable resistor
2. Define a series circuit
3. Show the formula depicting five resistors in a series circuit
4. Describe Ohm’s Law
5. Draw and Calculate the total resistance in a series circuit containing two 1.5 ohm light bulbs, a battery, a 1 ohm buzzer, a switch, and a 5 ohm motor
How do series and parallel circuits work?
Rtotal = R1 + R2 + R3...
Individual resistances (W)
Light bulbs, resistors, motors, and heaters usually have much greater resistance than wires and batteries.
How much current flows in a circuit with a 1.5-volt battery and three 1 ohm resistances (bulbs) in series?
Each separate resistance creates a voltage drop as the current passes through.
As current flows along a series circuit, each type of resistor transforms some of the electrical energy into another form of energy
Ohm’s law is used to calculate the voltage drop across each resistor.
16. What are the two advantages of a parallel circuit?
17. Describe a short circuit
Parallel circuits have two big advantages over series circuits:
1. Each device in the circuit sees the full battery voltage.
2. Each device in the circuit may be turned off independently without stopping the current flowing to other devices in the circuit.
Two bulbs with different resistances are connected in parallel to batteries with a total voltage of 3 volts.
Calculate the total current supplied by the battery.
19. Describe the resistance in a parallel circuit
20. Write the formula for calculating total resistance in a parallel circuit
21. A circuit contains a 2 ohm resistor and a 4 ohm resistor in parallel.
Calculate the total resistance of the circuit.
How do we analyze network circuits?
V0 = R1 Vi
R1 + R2
A bulb with a resistance of 1Ω is to be used in a circuit with a 6-volt battery.
The bulb requires 1 amp of current.
If the bulb were connected directly to the battery, it would draw 6 amps and burn out instantly.
To limit the current, a resistor is added in series with the bulb.
What size resistor is needed to make the current 1 amp?
25. Three bulbs, each with a resistance of 3Ω, are combined in the circuit in the diagram
Three volts are applied to the circuit.
Calculate the current in each of the bulbs.
26.From your calculations, do you think all three bulbs will be equally bright?
27.Describe Power in reference to electricity
28. How is power calculated?
29. What is the unit for power?
30. Describe a kilowatt
31. Describe horsepower
How much does electricity cost and what do you pay for?
P = VI
A light bulb with a resistance of 1.5Ω is connected to a 1.5-volt battery in the circuit shown at right.
Calculate the power used by the light bulb.
Your electric company charges 14 cents per kilowatt-hour. Your coffee maker has a power rating of 1,050 watts.
How much does it cost to use the coffee maker one hour per day for a month?
34. Define direct current
35. Define alternating current
36. What is meant by 60Hz alternating current?
For a circuit containing a motor, the power calculation is a little different from that for a simple resistance like a light bulb.
Because motors store energy and act like generators, the current and voltage are not in phase with each other.
The current is always a little behind the voltage.
Electrical engineers use a power factor (pf) to calculate power for AC circuits with motors
Avg. current (amps)
P = VI x pf