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What is the difference between p+ and e-? movement? What is the difference between insulators and conductors? What is charge sharing?
- Electrons are mobile. they can move easily. While p+ are not mobile. They are "locked up" in the nucleus.
- Insulators do not allow electrons to flow through them, for e.g. plastic, rubber, glass, air. These are the materials that can acquire a static charge. Conductors allow electrons to move through them easilt. Metals are conductors. because of this Metals do not acquire static charges.
- Charge sharing occurs when 2 identical objects are touched together, their total charge is shared equally between the two objects.
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What do like charges and unlike charges do? What is a negative and positive static charge?
Like charges exert repulsive forces on one another, while Unlike charges exert sttractice forces on each other. A negative static charge is an object with excess e-. A positive static charge is an object with more p+ than e-.
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What are the three ways to put a static charge on an object?
- 1. Friction - when two substances (insulators) (e.g. fur and plastic) are rubbed together electrons are transferred from one object to another (fur->plastic).
- 2. Induced charge (charging by induction) - when a charged object is brought near (not touching) a neutral insulator the neutral charge experiences an induced charge as the oppositely charged particles move closer and the similar charged ones repel.
- 3. Conduction - Direct contact with a charged object causes the excess electrons from the negatively charged objects to spread out evenly, causing the object that is touched to gain the same charge as the charged object. This causes both objects to repel aftwerwards.
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What is a coulomb? How many coulombs is one excess e-,p+ and an alpha particle equal to?
A coulomb is a unit of measuring static charges (static charges are often measured in micro (x10^-6) or nano (x10^-9) coulombs. One excess e- is equal to the negative elementary charge which is 1.60x10^-19C. One excess p+ is equal to the positive elementary charge and one alpha particle is equal to 3.20x10^-19C.
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What is an electroscope? What is Coulombs law?
- It is a device that is fully a conductor with two leaves on the bottom. It responds to static electricity.
- Coulombs law is used to determine the magnitude of Fe, we use logic to decide direction (either attraction or repulsion).
- The formula is Fe = kq1q1/r². Where Fe equal the magnitude of the electric force (N) between two point charges. K is Coulomb's constant (8.99x10^9 Nm²/C²). q1 and q2 are the charges (C) on the point charges (will be kept positive). and r is the seperation distance (m) between the 2 point charges.
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What is electric field theory? What is to note?
Electric fields are vectors ( E+ ߯), they point in the direction that a positive "test charge" (proton) would accelerate if released at a point. Note E+ ߯ is electric field (n/c) while E is energy (J). E + ߯ points away from postive point charges and towards negative point charges. E+ ߯ lines can be curved if you have 2 charges.
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How do you calculate electric fields?
|E + ߯| can be calculated form the formula |E+ ߯|=kq/r^2. Where |E+ ߯| is the magnitude of the electric field (n/c), k is 8.99x10^9 Nm^2/C^2, Q is the charge (C) of the point charge causing the formula (do not use direction) and r is the distance from the point charge (m). Remember since this is a magnitude direction is found with your positive point charge. If you don't have information about what is causing the field you can use E+ ߯= (Fe+ ߯)/q. Where E + ߯ is the electric field (with direction), Fe+ ߯ is the electric force (N) acting on a test charge in the field and q= is the magnitude of the charge (C) on the test charge.
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How do you use conservation of E with electron plates? Where does an e- have max Ep? How much is 1ev?
Since Ek=Ep you can find Ep with E=Vq and convert to Ek = 0.5mv^2. An electron has the maximum amount of Ep when it is closest to the like charged plate. An electron volt is a equal to the energy a electron has in an electron plate system with a one volt battery it is equal to 1.60x10^-19J.
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What was Milikan's oil drop experiment?
It was an experiemtn done by experimental physcist Milikan to determine the elementary charge (charge of one e-). To do this he used a spray bottle of oil, that sprayed statically charged oil droplets and began spraying droplets between electric plates with an adjustable power supply. He carefully adjusted the volts until adroplet was suspended (Fg=Fe). He then used the formula mgd/V = q and found the static charges of the oil droplets (he got mass from the volume and density of the oil droplets) He observed these charges were all multiples of 1.60x10^-19 so he suggested that was the charge of one e-.
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What are Magnets? What are magnetic domains and what metals can become magnets? What is different about bar magnets? Which direction does a compass point in?
- Magnets are metals that are made up of magnetic domains (microscopic volumes where electron spin direction is the same). These metals are Fe(s), CO(s), Ni(s) and ferromagnetic elements. Magnets are defined by a N and S pole. Like poles repel and unlikes attract.
- Bar magnets have a non-uniform magnetic field that is strongest at the poles and flows from N to S. When there are unlike poles together a uniform magnetic field is created.
- A compass always points in the direction of the magnetic field (vectorB)
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