[Science]: Electricity & Magnetism: Electric Charge and Static Electricity (Student Teacher's Notes)
What happens when grass seeds on a film of oil are exposed to an electrical field?
(textbook pg. 144 figure 5.10, pic on phone): Exposure to an electrical field makes grass seeds on a film of oil place themselves spontaneously along the electrical field lines.
See the textbook pg. 144 figure 5.10 (pic on phone), and describe what is happening in the picture at the right depicting electrical field lines of two parallel plates carrying opposite charges.
- Arrows show that the electrical field lines point away from the positive charges - Arrows show that the electrical field lines point towards the negative charges - In the middle, since the opposite charges (positive and negative) attract, the arrows point from the positive charges to the negative charges (since the arrows by convention point AWAY from the positive charges, and arrows point TOWARDS the negative charges)
What do atoms contain?
1. Protons (+) 2. Neutrons (0) 3. Electrons (-)
How can you charge objects?
3 ways: Friction Conduction Induction *For each way, only the electrons move. Protons stay in the nucleus.*
Coulomb's Constant
9x10⁹ Nm²/C²
[Txtbk pg. 172 #2]: The five spheres (look on pic as phone), identified A to E, carry an electrical charge. If sphere A carries a positive charge, what is the sign of the charges on each of the other spheres? Explain your answer.
A and B repel each other. A carries a positive charge. Since they repel each other, B carries a positive charge as well. B and C attract. Since B is positive, C will be negative. A and D also attract. Recall that A is positive and therefore D must be the opposite charge, which is negative. D and E repel each other. Recall that D carries a negative charge, so E must carry a negative charge as well.
What Is Electricity?
All phenomena caused by positive and negative charges
Define electrical field.
An electrical field is the area of space in which the electrical force of a charged body can act on another charged body.
All matter is made up of ______.
Atoms
What is the convention of electrical field lines?
By convention, electrical field lines point away from positive charges and toward negative charges.
What are the units for Coulomb?
C, coulombs
When does conduction happen?
Charging by conduction happens when electrons move from one object to another through direct contact (touching).
When does friction occur?
Charging by friction occurs when electrons are "wiped" from one object to another.
When does induction happen?
Charging by induction happens when charged in an uncharged object are rearranged without direct contact with a charged object.
What's an example of friction?
Cloth and ruler (cloth rubbing plastic ruler). Electrons move from cloth to ruler. Ruler gains electrons and cloth loses electrons.
Conductors are used to make what? Provide an example.
Conductors are used to make wires. Example: a lamp cord has metal wire and metal prongs. Prongs: each of two or more projecting pointed parts at the end of a fork (look up photo of it if you are unclear on it)
What three categories describe how objects react on receiving electrical charges?
Conductors, semiconductors and insulators.
What metal is the most ideal conductor?
Copper... it is a transition metal
What does Coulomb's Law state?
Coulomb's Law states that the magnitude of the force between 2 immobile and electrically charged particles is directly proportional to the product of their charges and inversely proportion to the square distance between them. In other words, the force between 2 charged objects is directly proportional to the charge of the particles and distance between the objects.
How do objects get charged?
Either gain or lose electrons
How are electric field lines displayed?
Electric field lines point away from positive charges and towards negative charges.
What are examples of electric discharge?
Electric shocks, and also lightning.
Describe the law of conservation of charge.
Electrical charges can neither be created nor destroyed; they can only be transferred from one body to another.
Describe the interaction between electrical charges.
Electrical charges interact with one another. Any electrically charged body placed near another charged body is subjected to an electrical force. This force is capable of what physicists call action at a distance, which means that charged objects are affected by the force without actually coming in contact with one another.
How can electrical fields be represented? Explain.
Electrical fields are invisible. However, they can be represented by electrical field lines, which are lines showing the direction of the force that would be exerted on a positive charge placed in the field.
What other type of substance also conducts electrical charges?
Electrolytic solutions: these substances contain *ions*, which are electrically charged particles. When electrodes are placed in an electrolytic solution, the positive ions move toward the negative terminal, while the negative ions move toward the positive terminal (see figure 5.6 pg. 142, pic on phone). Metals and electrolytic solutions are therefore usually good conductors. Electrolytic solutions are good conductors because the ions transport charges around.
Coulomb's Law Formula Label its components.
Fe=k(q1q2/r²) *e should be written as a subscript* Where Fe is the electrical force in N, newtons k is Coulomb's constant (9x10⁹ Nm²/C²) q1: charge of the first particle (in C) q2: charge of the second particle (in C) r: distance between the 2 particles (in meters)
What are the differences between friction, conduction and induction?
Friction - When an object whose electrons are loosely held rubs against another object, electrons are transferred to the second object... involves two neutral bodies Conduction - When an object with an excess of electrons touches a neutral object, electrons are passed to the neutral object. and... Induction - A neutral object acquires a charge from a charged object close by without contact being made In short: Friction -- 2 neutral objects -- friction pulls electrons away from one of the objects and transfers them to the other -- results in two objects with opposite charges. Conduction -- one charged object and one neutral object -- the charge of one object is shared between two objects when they come into contact -- results in two objects with like charges Induction -- one charged object and one neutral object (like conduction) -- the proximity of the charged object causes the charges in the neutral object to separate -- results in one charged object and one object carrying a partial positive charge on one side and a partial negative charge on the other side.
What terms are associated with static electricity?
Friction, conduction, induction and Coulomb's Law.
Describe how electrical discharge works.
From the textbook (pg. 145): Electrically charged objects don't remain permanently charged. Sometimes they gradually lose their charge, for example, by combining with water molecules in the surrounding air. This loss explains why the effects of static electricity are less frequent during humid weather. In other cases, however, charged objects recover their neutral state (having no charge) very quickly. This happens when 2 objects of opposite charges come close to each other or touch. The result is referred to as an *electrostatic discharge*. The discharge is sometimes accompanied by a spark, which shows that electrons have passed through the air and heated it, making it light up. For example: a lightning bolt; involves the rapid neutralization of two charged objects (for example, a cloud and the ground).
Explain a little more how induction works.
Induction refers to an action that occurs without direct contact between objects, When an electrically charged object approaches a neutral object without actually touching it, opposite charges will gradually accumulate on the other side of the neutral object that is facing the charged object (remember: like charges repel, so the like charges will repel and go to the other side of the object, whereupon the opposite charges will attract and will face the charged object).
What happens when you charge a metallic conductor in a circuit?
It forces the electrons to move in one general direction. One electron "pushes" another, causing the charge to move along the length of the circuit.
[Txtbk pg. 172 #1]: Vanessa observes that an object is positively charged. Has it gained or lost electrons? Explain your answer.
It has lost electrons. Remember the first chapters? When it becomes more positive, that means it has lost electrons.
Describe how an object would acquire a charge.
Most objects are electrically neutral, meaning they carry an equal number of protons (positive charges) and electrons (negative charges). However, by transferring electrons from one atom to another, some objects can acquire a charge. This process is known as charging an object. Therefore, charging an object consists in creating an imbalance in the electrical charge of that object.
Provide examples of good insulators.
Nonmetals, wood, plastic, glass, paper, ceramics, rubber, silk and air.
See the electrical field lines in workbook pg. 76
Ok
What are semiconductors? Provide examples.
Other substances exhibit variable conductivity, depending on different factors. These substances are called semiconductors and are widely used in electronics, particularly in the manufacture of transistors (semiconductor device used to amplify or switch electronic signals and electrical power). Metalloids and carbon are examples of semiconductors.
What are good insulators?
Plastic, rubber, glass, wood and air
Mnemonic for the triboelectric series.
Pressed Schedules Gulp New Hamsters When Cyan Parsnips See Lumpy Wealthy Giblets -- Plastic Sulphur Gold Nickel, copper Hard rubber (ebonite) Wood, yellow amber, resin Cotton Paper Silk Lead Wool Glass
During a storm, impressive bolts of lightning form jagged lines across the sky. The lightning is caused by a brief but powerful electrical discharge. If the electrical discharge of a lightning bolt is equal to 20 C, how many electrons were involved in the neutralization process?
Recall that 1 C = the charge on 6.25 x 10 ¹⁸ electrons (or protons). To get the number of electrons (or protons, but it's electrons in this case), multiply the number of Coulomb's by 6.25 x 10¹⁸ electrons since 1 C = the charge on 6.25 x 10 ¹⁸ electrons (or protons). 20 C x (6.25 x 10 ¹⁸) = 1.25 x 10²⁰ electrons were involved in the neutralization process.
[Txtbk pg. 172 #4]: After charging a piece of fabric, Jonathan calculates that it has lost 2 x 10¹⁵ electrons. What is the charge in coulombs? Is this charge positive or negative? Explain your answer.
Recall that 1 C = the charge on 6.25 x 10 ¹⁸ electrons (or protons). We know that it has lost 2 x 10¹⁵ electrons. To derive the number of Coulomb's from this, divide: 2 x 10¹⁵ electrons ÷ (6.25 x 10 ¹⁸) = 3.2 x 10⁻¹⁴ C, Coulombs (that is the charge). This charge is negative because we're dealing with electrons.
What happens when an insulator is charged? Explain why.
Recall that an insulator is a substance that impedes the free flow of charges. When an insulator is charged, the charges do not move (figure 5.8 in textbook pg. 143, pic on phone). At the atomic level, insulators hold on tightly to their valence electrons, making it difficult for the electrons to leave the atom.
What is static electricity?
Static electricity describes all the phenomena related to electrical charges at rest.
In static electricity, charges can move from one object to another through friction, conduction and induction. Then why is static electricity defined as "all phenomena related to electric charges at rest"? (since the charges move)
Static means the charges are still because they can't move where they'd like to go where there is no conductor linking them.
What is the definition of The Coulomb?
The Coulomb is the unit of measurement for electrical charge. One Coulomb is equal to the charge of 6.25 x 10¹⁸ electrons or protons
What is happening at the atomic level of a metallic conductor?
The attraction between the nuclei of the metal atoms and their valence electrons is weak. The valence electrons can therefore easily pass from one atom to another.
Describe the concept of an electrical "field".
The concept of a "field" is often used to explain how a force can act over a distance. Imagine that a charged object produces an electrtical field and that this field acts as an intermediary (a person who acts as a link between people in order to try to bring about an agreement or reconciliation; a mediator: a go-between), transmitting an electrical force to any charged object that crosses the field.
What will happen if you place a positively charged rod to a negatively charged electroscope?
The electrons are attracted to the rod because of opposite charges. (figure 5.11 on textbook pg. 145, pic on phone)
What will happen if you place a negatively charged rod to a negatively charged electroscope?
The electrons are pushed toward the foil strips. Basically, they will repel each other to the rod. When the knob of the electroscope is touched with a charged object, the charge is transmitted to the metal rod. Since the two foil strips at the end of the rod acquire the same charge, they repel each other. (figure 5.11 on textbook pg. 145, pic on phone)
What happens when an insulated metallic conductor is charged?
The electrons in it move rapidly, distancing themselves from one another as much as possible. A new balance is quickly re-established, in which the charges spread out uniformly over the surface of the conductor (Figure 5.5 in textbook pg. 142, pic on phone), while the inside of the conductor remains neutral.
What is the charge of one electron?
The elementary charge is the charge carried by a single electron or proton. It has a value of 1.602 x 10⁻¹⁹ C
Describe the nature of an electrical field.
The field is at its strongest near the charges, so the lines around them are close together.
Electrical field lines
The first circle is represents a positive charge and the second circle represents a negative charge.
What is the electrical force?
The force at work in the attraction or repulsion between charges.
What is an example of a conductor?
The human body conducts electricity! In figure 5.7 on page 143, pic on phone, charges are acquired through contact with a Van de Graaf generator (that machine). The charges then spread uniformly across the entire surface of the body. Charged hairs seek to move as far away from one another as possible (because they are like-charges).
What is an example of an insulator?
The insulating material in a lamp cord stops charges from leaving the wire and protects you from electric shock.
What is the law of electrical charges?
The law of electric charges states that like charges repel, and opposite charges attract. Protons are positively charged and electrons are negatively charged, so they are attracted to each other
What is electric discharge?
The loss of static electricity as charges move off an object is called electric discharge.
What happens when objects have opposite charges? (law of electric charges)
The objects are attracted to each other. Each object exerts a force on the other object. These forces pull the objects together.
What happens when objects have the same charge? (law of electric charges)
The objects repel each other. Each object exerts a force on the other object. These forces push the objects apart.
What is induction?
The production of a charge in an uncharged body by bringing a charged object close to it. When negatively charged rod is put near a metal can... the rod has a negative charges. The metal can has positive and negative charges. Because they have the same negative charge, the negative charges go to the other side away from the rod, and the positive charges go towards the rod. What happens is repulsion. Top of the can: positive, bottom of the can: negative.
What are factors affecting how well a material conducts? Identify the extreme that allows for better conduction of a material by putting it in parentheses. Note that the items in parantheses won't be dictated to you by the robot.
Type of materials (metals) copper is best Length (short) longer it is, narrower it is, therefore not good conductivity. Diameter (larger diameter = more room for conductivity). Temperature (lower temperature). Cold = solid atoms. The more solid, the better the conductivity.
If one Coulomb = charge of 6.25 x 10¹⁸ electrons or protons, how is it that the charge carried by a single electron or proton is 1.602 x 10⁻¹⁹ C?
We measure charges in C, coulombs. Coulombs is just a unit of measurement. (if you're curious, a coulomb is equal to the quantity of electricity conveyed in one second by a current of one ampere). With this in mind, 1 proton or electron has a charge of 1.602 x 10⁻¹⁹ C. That represents how many coulombs are in one proton or electron one Coulomb = charge of 6.25 x 10¹⁸ electrons or proton. This represents how many protons or electrons are in one Coulomb.
How does friction work?
When 2 different materials are pressed or rubbed together, the surface of one material will generally steal some electrons from the surface of the other material.
Give an example of charging by friction.
When a glass rod is rubbed against silk, the silk atoms pull some electrons away from the glass atoms. The silk temporarily acquires a negative charge, and the glass, a positive charge. Looking at the triboelectric series, you could see that since silk is higher up than glass, the silk will most likely capture electrons, and the glass will most likely give up electrons.
Describe how charging by friction works.
When two neutral bodies are rubbed against each other, some atoms in one of the bodies may pull electrons away from the atoms of the other body. The result is two bodies with opposite charges. The direction of this transfer depends on the tendency of the materials to capture or give up electrons. Table 5.14 in textbook pg. 146, pic on phone, provides some examples. A substance at the top of the list, called the triboelectric series, is more likely to acquire a negative charge than a substance at the bottom.
What is conservation of charge?
When you charge something by any method, no charges are created nor destroyed. The numbers of electrons and protons stay the same. Electrons simply move from one atom to another (remember covalent and ionic bonds?)
If the law of conservation of charge states that the total number of positive charges is always equal to the number of negative charges, so that the overall charge remains neutral, how come objects can get charged?
Whenever an object gets a negative charge, that means another object got a positive charge, and vice-versa. If you take these two objects, the amount of positive and negative charges is the same (might be concentrated in different places, however)
What's an example of induction?
You charge a balloon through friction and place the balloon near pieces of paper, the charges of the paper will be rearranged and paper will be attracted to the balloon.
What's an example of conduction?
You touch an uncharged piece of metal with a positively charged glass rod. Electrons move from metal to glass rod. Metal loses electrons and becomes positively charged.
What is an electrical conductor?
a material in which charges can move easily.
What is an electrical insulator?
a material in which charges cannot move easily
Why are most metals good conductors?
because some of their electrons are free to move
Why don't insulators conduct charges very well?
because their electrons cannot flow freely.
What is Coulomb's Law for?
between 2 objects that aren't moving... formula is only valid for objects at rest.
Elementary charge
e ≈ 1.6×10⁻¹⁹ Coloumb
Prongs
each of two or more projecting pointed parts at the end of a fork. (look up photo of it if you are unclear on it). It's like a fork, but with two ends instead of four.
What is the symbol for Coulomb?
q
What is an electric field?
the region around a charged object where electric forces can be exerted on another charged object (repelled or attracted)
What is the difference between static and dynamic electricity?
• Flow of electrons in a material is termed as electricity • In case of static electricity there is no flow of electrons and it is a result of imbalance of positive and negative charges only. The electrons remain stationary and do not move. • In the case of dynamic electricity, the flow of electrons can be either in a single direction (direct current), or it can be changing directions repeatedly (alternating current).
