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Chapter 67: Electric Power and Energy

- Light and heat can be produced using electrical energy.
- Electricity can be used to turn a motor.
- The amount of power and energy being produced can be determined by measuring the voltage and current in a circuit.
- J/C is a measure of the energy supplied to each coulomb of charge in the circuit.
- The total number of coulombs per second is measured by the current.

- We know that the energy is given by VIt, where it must be in seconds.

- The chapter is about to explore the laws of charge and energy.
- The following rules for circuits were given to us by Gustav Kirchhoff.

- The junction rule says that the total current coming into a junction must be equal to the total current leaving the junction.

- As you travel around a closed loop of a circuit, the total voltage drops and gains must total to zero.
- A voltage drop against the current is called a gain.
- From positive to negative is a voltage gain and from negative to positive is a voltage drop.

- The current coming into the junction on the left is 9 Amps, so a total of 9 Amps must be leaving.
- Since the other two branches are carrying a total of 8 Amps, 1 Amp is left for the missing pathway.

- I give you -2 V as a representation of the voltage dropping across the R 1 Resistor.
- As we traced through this resistor from right to left, we were able to get the decrease in voltage result.

- Two or more resistors are placed within a circuit.
- An example is shown.

- We need to ask some questions.

- Imagine a series of doors, one after the other, as a way to think about this circuit.
- People must wait to open another door as they exit one door.
- The result is a decrease in the number of people leaving the room.
- Adding more resistors in a series increases the resistance of the circuit.

- All of these observations can be summarized as follows.
- We have three currents in the resistors R 1, R 2 and R 3.

- The source voltage V is more than 888-738-5526 888-738-5526.
- The source voltage would be equal to one-third if all three resistors were equal.

- The three currents are equal, so they can be canceled out of the expression.

- The total resistance of the circuit increases as the number of resistances increases.
- As more resistors are added, the current decreases.

- The circuit current of 12/6 is 2 A since the source voltage is 12 V. The same current of 2 A can be used to determine the voltage across each Resistor.

- When batteries are connected in series, the effective voltage increases as well.

- A parallel circuit consists of pathways connecting from one point to another.
- An example of a parallel circuit is shown.

- I 1 and I 2 are split into a branch point in this circuit.
- Experiments verify that the source V is the same as the source V across the resistors.
- The current is shared and the voltage is the same.
- Alternative paths are a feature of the parallel circuit.
- Current can flow through the other path if one part of the circuit is broken.
- The effect of adding resistors in parallel is to increase the effective circuit current by decreasing the circuit resistance.

- Imagine a set of doors next to each other in a room.
- The parallel-circuit analogy involves placing the doors next to each other.
- The effect is to allow more people to leave the room even though there will be less people going through each door.
- Reducing the circuit resistance and increasing the circuit current are the same thing.

- These observations can be expressed as follows.
- R 1 and R 2 have currents I 1 and I 2.

- The expression indicates that the total resistance is determined "reciprocally", which reduces the total resistance of the circuit.
- There is no effect on the overall voltages of the batteries if they are connected in parallel.

- The 20- and 5-resistors are connected to each other.
- If a 16-V battery is used, calculate the equivalent resistance of the circuit, the circuit current, and the amount of current flowing through each resistor.

- It is easy to see that R eq is 4.

- To find the current in each branch, we have to remember that the voltage drop across each Resistor is the same as the source voltage.

- The total current is the same as expected.

- A circuit that consists of resistors in parallel and series is presented.
- The key to reducing such a circuit is to decide if it is a series or parallel circuit.
- A parallel branch with two 4-resistors is placed in a series.
- To determine the circuit current, the voltage reading in the voltmeter, and the current reading in the meter, you have to reduce the circuit to only oneresistor.

- Reducing the parallel branch is necessary to find the circuit resistance R.

- R e is the number of resistance.
- The circuit can now be thought of as a series of circuits between a 2- and 8-resistor.

- In a series circuit, the same current flows through each resistor and the voltage drop across them is shared proportionally.

- In a parallel circuit, the voltage is the same across all the resistors.
- Since the two resistors are equal, each will get half of the circuit current, and the reading on the ammeter is 1 A.
- We used the rule at the junction to reduce the current.

- Questions on the AP physics 1 exam will be limited to one parallel path and one ideal battery in circuits.

- Many students of physics are confused by the fact that the current coming out of the resistor is the same as the current coming in.
- Many students think the energy of moving electrons is a type of energy called kinetic energy.
- The moving charges carry the electrical potential energy in the electric and magnetic fields.
- The electrons going into the resistor are different from the ones coming out.
- The fields associated with their relative positions are completely different even though the number of electrons passing per second is the same.
- All potential energies are related to the physical relationship between two or more objects.
- The slightly closer-spaced electrons before they enter the Resistor have more energy than the slightly farther apart electrons leaving the Resistor, just as 5 fully extended rubber bands moving past you at 5 mph have more total energy than the same 5 slack rubber bands moving past you at the same speed

- The strongest example of field energy for electricity is in light.
- As the light goes from one place to another, it is carrying energy.
- There are other potential energies that can be used to make parallels.
- The rock's potential is stored in the field between the rock and the Earth.
- The block at the end of the spring does not hold the elastic energy of a stretched spring.

- Positive and negative electric charges exist.

- Electrons have a negative charge.

- There is a positive charge.

- Like charges repel, unlike charges attract.

- The presence of static charges can be detected with an electrical device.

- The objects are charged by the transfer of electrons.

- The force between two static charges is described by Coulomb's law.
- The force of attraction is proportional to the product of the charges and the force of repulsion is proportional to the square of the distance between them.
- The law of gravitation is similar to this one.

- The electrical potential difference is equal to the work done per unit charge.

- Electric current is the flow of charge in units of amperes.

- The conventional current is based on a positive charge flow.

- At constant temperature, the ratio of voltage and current is a constant in a conductor.

- The material used, length, and cross-sectional area are all related to electrical resistance.

- Ammeters measure current and are placed within a circuit.

- The potential difference is measured and placed in parallel across segments of the circuit.

- A source of potential difference is needed for a simple circuit.

- Resistors connected in series have the same resistance as their numerical sum and carry the same current through each.

- The same potential difference can be experienced across parallel Resistors if they are connected in parallel.

- The flow of current in circuit branches and the changes in voltage around loops are described in the rules.

- There are several techniques for solving electric circuit problems discussed in this chapter.
- Series and parallel circuits are used for resistances with one source of emf.
- The determination of currents within the circuit and the potential drops across the resistors are measured by the Ohm's law.

- Try to reduce all subbranches first when working with a combination circuit.
- The goal is to be able to identify the missing quantities by using Ohm's law.
- If you don't have a sketch of the circuit, you need to.
- The direction of current is taken from the positive terminal.

- A is charged to a value of Q elementary charges.
- A neutral insulated metal sphere is touched and separated from it.
- The neutral insulated metal sphere C is touched to the second sphere.
- spheres A and C are separated after being touched.

- 10 A of current is present in a 20-resistor.

- One source of negligible internal resistance is the only source of emf connected to the 5- and 10-resistors.

- Four lightbulbs are arranged in a circuit.

- Four point charges are arranged in the same way as shown below.

- A rod attracts a sphere.

- Platinum wire is wound into a coil.

- A laboratory experiment uses lightbulbs.
- The current readings decline after a while.

- Sphere A and B have zero charges.
- Each sphere will have half of the total charge when it is touched and separated.
- Each now has + Q.

- We distribute the charge evenly when B and C are touched.
- B, C, and A all have + Q /4.

- When A and C are touched, we take the average of + Q /4 and + Q /2, which is +3 Q /8.

- The final distribution is 3 Q -8, Q -4, and Q -8.

- Everything except one charge is given.

- The charge is equivalent to 10 18 electrons.
- 2 A for 2 s is equivalent to 2.5 x 10 19 electrons.

- The two resistors are in a series.
- R is 4.

- The source current must be added to the branch currents.
- We can see that the current in the 2-resistor is 6/2 because of the Ohm's law.
- The current in R must be equal to 1 A.

- The 10-resistor has twice the resistance of the 5-resistor in series.
- When the circuit is on, the 10-resistor will generate twice as much energy as if the currents were equal.

- There will be a greater potential difference across D than across the equivalent resistor.
- The equivalent resistance will generate less power than the currents will allow.
- With the current split for the parallel part, there will be less energy available for the resistors A, B, and C. Bulb D will be bright.

- The lower- left-corner charge will experience mutual repulsions from the other three since all the charges are positive.

- Coulomb's law gives the magnitude of each force.
- The Pythagorean theorem was used to determine the diagonal distance.

- F-1 acts to the left and F3 acts to the right.
- F-2 acts at an angle to the lower left.
- To find the angle, we have to use the sides of the rectangle.
- F-2 will be negative by our sign convention.

- The net force acting on the lower left corner charge is the sum of the charges.

- The ph is relative to the x - axis.

- The only conclusion you can make is that the sphere is neutral or oppositely charged.

- The charges are distributed around the outside of the car if it is hit by lightning.
- This acts like a shield.

- R is the resistance needed.
- The cross-sectional area is what we need.

- There is an equivalent resistance of 8 O + 2 O.
- The resistance is in close proximity to the other one.
- 5 is the equivalent resistance for the entire parallel branch.
- The total equivalent resistance of 10 is made up of this resistance and the other 5-resistors.

- There is a potential difference of 20 V between the parallel branch's resistance and that of the entire branch, because the parallel branch's resistance is also 5.
- The potential difference is the same across the circuit.
- The 10-resistor has 20 V across it.
- We find that this means a current reading of 2 A for ammeter A.

- The emf of the system is not changed when two batteries are connected in parallel.
- Since the parallel connection of the two batteries is similar to the parallel connection of two capacitors, the storage capacity of the battery system is increased.

- The equivalent resistance of 1 can be achieved by connecting two 2-resistors.
- An equivalent resistance of 3 can be achieved by connecting two 2-resistors in parallel and then one 2-resistor in a series.

- Lightbulbs produce their energy by heating up the inside of them.
- Since the resistance has increased, this increase in temperature reduces the current flowing through them.

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