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Chapter 63: The Detection and Measurement of Electric Charges

- The part of the rod in contact with the cloth becomes charged when ebonite is rubbed with cloth.
- The name static refers to the charge being local for some time.
- Among others, rubber, plastic and glass are called insulator.
- There are two reasons a metal rod cannot be charged statically.
- Electric charges can flow through metals as conductors.
- Your body is a conductor and any charges placed in the metal rod are conducted through you.
- The effect is called grounding.
- The silver-coated pith balls mentioned in the first section of this chapter can become statically charged because they are suspended by thread.
- They can be used to detect the presence and sign of an electric charge, but they are not very helpful in obtaining a qualitative measurement of the magnitude of charge they possess.

- The electroscope is used for qualitative measurement.
- There are two "leaves" made of gold foil.
- The leaves are vertical when the scope is not charged.
- The leaves change color when a negatively charged rod is near.
- If we recall the hypothesis that only negative charges move in the air, we can understand that the electrons are repelled down to the leaves through the conducting stem.
- As long as the rod is not touching the knob, it will become positively charged.
- The leaves will collapse if you take the rod away.

- The electrons are transferred to the knob, stem, and leaves.
- The whole scope becomes negatively charged.
- The extent to which the leaves are spread apart is an indication of how much charge is present.
- The leaves will collapse if you touch the electroscope.

- The electroscope can be charged with electricity.
- The repelled electrons will be forced out into your body if you touch the electroscope with your finger.
- The electroscope will have a positive charge if you remove your finger.

- We can state that electric charges obey a law.
- We always maintain a balanced accounting when we transfer charge.
- We have metal spheres.
- Both sphere A and sphere B have positive elementary charges.
- The two spheres are near each other.
- Since they repel each other, excess charges are spread out as far apart as possible.
- If the net charge on both objects is positive, the electrons will move even if the charges are allowed to flow.
- If the two spheres are equal in size, each will have a +3 charge if enough electrons move from the +2 sphere to the +3 sphere.
- If one object is larger than the other, the larger object will have more of the net excess charge spread out around the outer surfaces of the combined object.

- We can conclude from the first two sections of the chapter that charges repel each other, and unlike charges attract.
- The force between two charged objects can move through space.
- The force of gravity is similar to the force of this property.

- The charge is measured in coulombs.

- The inverse square law is very similar to the law of gravitation.
- The force of gravity can be mitigated by the electrostatic force.
- There can be repulsion as well as attraction.

- The nature of the force was studied by a French scientist.
- The force between q 1 and q 2 was caused by a mutual force along a line connecting the charges that varied directly as the product of the charges and the square of the distance between them.
- The inverse square law of Coulomb's law is similar to the law of gravity.

- M 2 /C 2 is 9 x 10.

- Coulomb's law is similar to the law of universal gravitation.
- The two point sources are connected by a radial vector.
- Coulomb's law only applies to one pair of point sources or sources that can be treated as point sources, such as charged spheres.
- The net force on one charge is the sum of all the other forces.
- Superposition is an aspect of force addition.

- The force is attractive because of the negative sign.

- F 1 is the electric force of 175 mC charge.
- It will go straight up.

- F 2 is the electrical force of the charge.
- It will go straight to the right.

- Negative charges will flow from a higher concentration to a lower one if two points are connected with a conductor.
- This part of charge flow is very similar to the flow of water in a pipe.

- The amount of charge passing a point every second is referred to as electric current.
- The units of measurement are coulombs.

- The battery supplies the potential difference needed to maintain a continuous flow of charge.
- Physicists thought that the electric force pushed the electric fluid through the conductor.
- We know that an emf is not a force but a potential difference.

- A battery uses acids and bases on different metals to free electrons and maintain a potential difference.
- Two terminals are created in the process.
- A complete circle of wire is produced when a conducting wire is looped around the other end.
- The battery uses chemical reactions to raise electrons from the positive side to the negative side.
- The electrons can transform their electric potential energy into other forms of energy.
- Our modern world has become familiar with the electricity of this work.

- A simple electric circuit is shown in the diagram.
- The direction of the conventional current is from the positive terminal.
- To maintain a universal acceptance of concepts and ideas, schematic representations for electrical devices were developed and accepted by physicists and electricians worldwide.
- When drawing or diagramming an electric circuit, it's important that you understand the basics of the schematic.
- Some of the most frequently encountered electrical devices are presented in the schematic.

- The simple circuit shown in can now be diagrammed.

- The charge would not flow unless the switch was closed.
- An open switch stops the flow.

- We have not yet discussed three of the schematics.
- The function of a Resistor is to use up voltage.
- In the next section, we will look at the resistors in more detail.

- An ammeter is used to measure the current.
- You can find the water meter in your house or apartment building by looking at the flow line.
- The meter has to measure the flow of water through a point.
- An electric circuit has an ammeter within it.
- The series connection maintains the singular nature of the circuit.
- You can imagine cutting a wire and hooking up the bare leads to the ammeter.
- Ammeters have low resistance.

- A voltmeter is a device that measures the potential difference between two points.
- The voltmeter can't be placed within the circuit since it will be connected to only one point.
- A second circuit through which only a small amount of current flows to operate the voltmeter is attached to a parallel connection.
- The simple circuit is redrawn with an ammeter.
- They have high resistance.

- The electric potential is the unit of electric potential.
- The amount of energy per charge is determined by the amount of energy between the two points.
- There are many terms used for this important concept in electricity.

- If the ammeter and voltmeter are moved to different locations, there will be no observable difference in readings.
- There is a slight difference in the emf between when the switch is open and closed.
- The work done by the battery is reflected in the first emf.
- The terminal emf is sometimes referred to as the internal emf.

- When a battery dies, it doesn't run out of power, it runs out of energy.
- The battery's voltage rating is a measure of how much energy the battery will give up to each charge.
- Until the battery runs out of energy, it will continue to do so.

- A simple electric circuit is illustrated with measuring devices.
- Two observations can be made if a lightbulb is on for a long time.
- The bulb gets hot because of the action of the electricity.
- The heat of the bulb causes it to light up.
- The current in the ammeter will decrease.

- The idea of electrical resistance is linked to these two observations.
- An electrical resistance is created by the interaction of flowing electrons and the molecule of a wire.
- The resistance is dependent on the temperature, since an increase in temperature will increase the activity of the molecule and interfere with the flow of current.
- Thermal energy is being converted to electrical potential energy.

- The resistance that is desired in order for the bulb to do its job is the same resistance that is desired in the case of a lightbulb.
- Resistance in a battery is unwanted and must be minimized.
- In more complicated circuits, a change in current flow is required to protect devices, and so special resistors are made that are small enough to fit into a circuit.
- Since insulators will stop the flow, we don't want to use them as resistance.
- A range of materials is catalogued in electrical handbooks to assist scientists and electricians in choosing the right Resistivity for a given situation

- The relationship between the voltage and the current in a circuit is revealed if the temperature can be maintained at a constant level.
- This direct relationship was investigated by a German physicist, called Ohm's law.

- In a circuit at constant temperature, the ratio of the voltage to the current remains constant.
- The resistance of the circuit is represented by the slope of the line.

- Some conductors don't obey the law.
- Liquid conductors, lightbulbs, and Semiconductors do not.

- The resistance of a conductor is affected by other factors.
- The effects of temperature and material type are already discussed.
- Resistivity is determined by the Greek letter r. The electrons try to move through the wire.
- The resistance of the wire increases if the wire has a small cross-sectional area.
- Increasing the length of the wire will increase the resistance of the wire.
- The resistance factors all contribute to the resistance of the circuit.

- The resistivity is usually rated at 20 degrees Celsius.

- The resistivities of various materials are presented.
- All lengths are in meters and areas are in square meters, since the ohm is a standard unit.

- The copper wire is being used.
- The wire is 1.2 m long and has a cross-sectional area of 8 m 2 at a constant temperature.

- 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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