Electric circuits
what they do
automatically open a circuit if the current becomes dangerously high
How does adding a light bulb to a series circuit affect the brightness of the bulb?
bulbs get darker
How CFLs produce less waste energy
compact fluorescent light bulbs conduct an electric current through a gas and do not use wire filaments so more energy is transformed into light and less is transformed into heat.
why series circuits are safer in holiday lights
current is lower because resistance is greater si little thermal energy is produced
Battery produces
electric current in a circuit
What causes fire
excess current
What are used as safety devices to prevent disasters in a parallel circuit?
fuses and circuit breakers
large power plants
generate the energy used in homes
ex.
if a hair drier is on and water is splashed on you and it, some of the electric current flows through you and not the hair dryer because water is a conductor.
Adding branches
increases current
A meter
is used to measure the amount of energy difference or "push" in a circuit. The meter reads the voltage difference (in volts) between the positive and the negative ends of the power source (the battery).
how the GFCI helps
it senses that not all of the current is flowing through the hair dryer and opens the circuit and stops the current, reacting as quickly as 1/30 of a second.
To determine the kilowatt-hours of electricity used,
multiply the number of kilowatts by the time in hours.
the current in one branch has
no effect on the current of other branches
metal wires are often used to connect in a circuit because
of their low resistance so they only transform a small amount of electrical energy into thermal energy
Since energy is measured in joules,
power is measured in joules per second. One joule per second is equal to one watt.
GFCI (Ground Fault Circuit Interrupter)
protects you from electric shock
How does taking away a light bulb to a parallel circuit affect the brightness of the bulb?
same brghtness
How does adding a light bulb to a parallel circuit affect the brightness of the bulb?
same brightness
Unlike series circuits when one appliance is turned off
the other are still on
Charges flow in a circuit when
there is a difference in energy level from one end of the battery (or any other energy source) to the other.
Power
voltage x current
If your town charges $0.15 per kWh, what is the cost to use the hair dryer for a month?
$0.90
If your town charges $0.15 per kWh, what is the cost to use the oven to bake the cookies?
$1.50
Calculate the cost of using the alarm clock for one year if your town charges $0.15 per kilowatt-hour.
$74.84
Convert the power to kilowatts.
0.06
the battery voltage is 20 volts. What will be the reading of the ammeter shown in the circuit? (one 20 ohm resister and one 30ohm resister)
0.4 amp
A circuit contains a 1.5 volt battery and a bulb with a resistance of 3 ohms. Calculate the current.
0.5 amps
Use the total current and the total voltage to calculate the total resistance of the circuit.
1.2 Ohms
A 1 , a 2 , and a 3 resistor in parallel
0.54 Ohms
What is the power in kilowatts?
0.6 Kilowatts
Using the formula for power, calculate the amount of current through a 75-watt light bulb that is connected to a 120-volt circuit in your home.
0.625 amps
How many amps of current flow through a circuit that includes a 9-volt battery and a bulb with a resistance of 12 ohms?
0.75 amps
How much current is in a circuit that includes a 9-volt battery and a bulb with a resistance of 12 ohms?
0.75 amps
Calculate the power rating of a home appliance (in kilowatts) that uses 8 amps of current when plugged into a 120-volt outlet.
0.96 Kilowatts
Use the total current and the total voltage to calculate the total resistance of the circuit.
1 Ohm
A circuit contains two 1.5 volt batteries and a bulb with a resistance of 3 ohms. Calculate the current.
1 amp
What is the current in the circuit?
1 amp
All parts of a circuit transform energy (3 ex)
1. Battery: chemical potential into electrical 2. Electrical devices (light bulbs) electrical into light 3. Wires Electrical to thermal
How?
1. Electric energy comes to your home through a main wire. 2. The main wire travels through an electric meter. 3. The meter measures the energy used in the electric circuits of your home. 4. From the meter, the wire enters your house and goes to a box called the main panel. 5. At the main panel, the main wire then divides into the branches of the parallel circuit.
How to stay safe (6 ways)
1. Never use damaged power cords 2. Stay away from water when using devices plugged into an outlet 3. Avoid using extension cords and never plug more than two home appliances into an outlet at once 4. Never allow any object that you are touching, such as a kite string or a ladder, to contact electric power lines. 5. Do not touch anyone or anything that is touching a fallen electric wire. 6. Never climb utility poles or fences that enclose electric power equipment.
How light bulb works
1. electrons flowing in the filament of a light bulb collide with the atoms that make up the filament 2. These collisions transfer the electrons energy to the atoms causing them to immediately release the energy into other form (such as light)
3 common parts of an electric circuit
1. source of electric energy 2. electrical devices that transform electric energy 3. conductors (wires) that connect the other components
What is the power of the hair dryer in kilowatts?
1.2 Kilowatts
Two 6 resistors and a 2 resistor in parallel
1.2 Ohms
A portable CD player uses two 1.5 V batteries. If the current in the CD player is 2 A, what is its resistance?
1.5 Ohm
How many amps of current flow through a circuit that includes a 9-volt battery and a bulb with a resistance of 6 ohms?
1.5 amps
Use the total current and the total voltage to calculate the total resistance of the circuit.
1.5 amps
If the oven is used for 2 hours to bake cookies, how many kilowatt-hours (kWh) are used?
10 Kilowatts
What is the total current provided by the batteries?
10 amps
What is the resistance of the dryer?
10.75 Ohms
How many ohms of resistance must be present in a circuit that has 120 volts and a current of 10 amps?
12 Ohms
What is the total resistance of a 20 ohm and a 30 ohm resistor in a parallel circuit?
12 Ohms
12 Volt battery one 2 ohm and one 3 ohm. What is the voltage across each resistor?
12 V
12 v battery and two 3 Ohm resisters. What is the voltage across each bulb?
12 V
A circuit contains a 12-volt battery and two 3-ohm bulbs in parallel. What is the voltage across each branch?
12 V
One 12V battery and two 2 Ohm resisters. What is the voltage across each bulb? What is the current in each branch? What is the total current provided by the battery?
12 V and 6 amps and 12 amps
Calculate the power of each bulb.
12 watts
What is the voltage of a circuit with 15 amps of current and toaster with 8 ohms of resistance?
120 amps
A parallel circuit with two 100-ohm resistors and a 20-ohm resistor.
14.29 Ohms
What is the total current provided by the battery?
16.5 amps
How many kilowatt-hours of electricity are used by the dryer if it is used for 4 hours in one week?
18 kilowatt-hours
Calculate the current in the circuit.
2 amps
Series circuit with one ampere of current
2 batteries and one 3 0hm bulb
How much voltage would be necessary to generate 10 amps of current in a circuit that has 5 ohms of resistance?
50 Volts
A 12 resistor and a 3 resistor in parallel
2.4 Ohms
A 4 resistor and an 8 resistor in parallel
2.66 Ohms
Three 8 resistors in parallel
2.66 Ohms
A clothes dryer in a home has a power of 4,500 watts and runs on a special 220-volt household circuit. What is the current through the dryer?
20.45 amps
A toaster is plugged into a 120-volt household circuit. It draws 5 amps of current. What is the resistance of the toaster?
24 Ohms
Calculate the power of a motor that draws a current of 2 amps when connected to a 12 volt battery.
24 Watts
Calculate the power supplied by the battery.
24 watts
An alarm clock draws 0.5 A of current when connected to a 120 volt circuit. Calculate its resistance.
240 Ohms
What is the difference between placing a 1.5-volt battery in a circuit and placing a 9-volt battery in a circuit?
There will be more current flowing
How much current is in a circuit that includes a 9-volt battery and a bulb with a resistance of 3 ohms?
3 amps
What is the current in each branch?
3 amps, 4.5 amps, 9 amps
You have a large flashlight that takes 4 D-cell batteries. If the current in the flashlight is 2 amps, what is the resistance of the light bulb? (Hint: A D-cell battery has 1.5 volts.)
3 ohms
What is the power of the light bulb?
3 watts
You use a 1,200-watt hair dryer for 10 minutes each day. How many minutes do you use the hair dryer in a month? (Assume there are 30 days in the month.)
300 minutes
What is the total voltage of the circuit?
3V
The battery voltage is 12 volts and their are 3 light bulbs that are all identical . What is the voltmeter reading?
4 Volts
Calculate the current in each branch.
4 amps
What is the current in each branch?
4 amps
6 amps of current
4 batteries and 1 ohm bulb
3 amps of current
4 batteries and 2 ohm battery
2 amps of current
4 batteries and one 3 ohm battery
Two 8 resistors in parallel
4 ohms
Calculate the power of each bulb.
48 in each
Your oven has a power rating of 5,000 watts. How many kilowatts is this?
5 Kilowats
How many hours do you use the hair dryer in a month?
5 hours
A parallel circuit with two 20-ohm resistors and a 10-ohm resistor.
5 ohms
Calculate the number of kilowatt-hours of electricity used by the alarm clock if it is left on for one year.
525.6 Kilowatt hours
A circuit contains a 12-volt battery and two 3-ohm bulbs in series. Calculate the total resistance of the circuit. (series circuit)
6 Ohms
What is the current in each branch?
6 amps and 4 amps
How many kilowatt-hours of electricity does the hair dryer use in a month?
6 kilowatt hours
Two 12 resistors in parallel
6 ohms
A parallel circuit with a 10-ohm, 20-ohm, 100-ohm and 200-ohm resistor
6.06 Ohms
A parallel circuit with a 20-ohm resistor and a 10-ohm resistor.
6.67 Ohms
Your alarm clock is connected to a 120 volt circuit and draws 0.5 amps of current. Calculate the power of the alarm clock in watts.
60 watts
What is the power of the toaster in watts?
600 Watts
A light bulb has a resistance of 4 ohms and a current of 2 A. What is the voltage across the bulb?
8 Volts
Calculate the total current in the circuit.
8 amps
What is the total current provided by the battery?
8 amps
A parallel circuit with a 15-ohm light bulb and a 20-ohm resistor.
8.57 Ohms
9V battery, 3 ohm resister, 2 ohm resister, and 1 ohm resister. What is the voltage across each resistor?
9 V
Calculate the power supplied by the battery.
96 Watts
Circuit with 2 1.5V batteries and a 3 ohm resister
:0
parallel circuit
An electric circuit with multiple paths for electric current to follow (home)
series circuit
An electric circuit with only one path through which charge can flow (most holiday lights)
How?
As chemicals in the battery react, they concentrate at the negative terminal
What happens to the current in a circuit if a 1.5-volt battery is removed and is replaced by a 9-volt battery
Current is flowing 6 times faster
Kirchoff's current law
If current flows into a branch in a circuit, the same amount of current must flow out again. (Iin=Iout)
How would you find the resistance of a parallel circuit with n identical resistors?
R=Resistance/Number of resisters
What will be the total resistance and current in a parallel circuit with a 15-volt battery and three 10-ohm resistors?
Total resistance: 3.3 Ohms Current: 4.5 A
This energy difference is called____________ and measured in ____________
a "gradient and is measured in volts.
Fuses
a piece of metal that melts and breaks a circuit when a high current produces too much thermal energy
circuit breaker
a switch that opens when the current in a circuit is too high
How does taking away a light bulb to a series circuit affect the brightness of the bulb?
all bulbs go out