PHY 182 1st EditionExam # 2 Study Guide Lectures: 11 - 15Lecture 11- All atoms are made of protons, electrons, and neutrons. An atom's number of protons and electrons determines its charge.- Atoms are considered to be neutral unless ionized.- The sum of electric charges in an isolated system is always constant (this is the law of conservation of charge).- Charge is quantized, which means that it comes it definite amounts and cannot be foundin smaller amounts than the fundamental unit of charge.- Coulomb created a law in which the electric force that is present between two charges can be calculated: F=kq1q2/r2, k being the electrostatic constant and r being the distance between the two charges.- There are two kinds of charge, positive and negative. The distinction between the two was chosen arbitrarily.- Protons and electrons have the same magnitude of charge, just opposite signs.- Objects can become charged if some of its electrons are added or removed. The atoms are then considered to be "ions".- An object with an equal number of protons and electrons is neutral, which means that ishas zero net charge.- Like charges repel and opposite charges attract.- Electric force is indirectly proportional to distance. So if the distance between two objects increases, the electric force between them decreases.- There are two types of materials: insulators and conductors. The charge remains fixed in or on an insulator. Charge can move easily through conductors.- Charge is transferred by contact between objects.- Charge objects attract neutral objects (important concept!), this happens due to the shifof electrons that occurs.- Charge polarizes atoms, creating electric dipoles.Lecture 12- It is important to remember that charge can never be created nor destroyed.- When something becomes charged, it is because it has been transferred from one material to another.- Michael Faraday observed that particles react to other charges in the same way that planetary bodies react, through long-range forces.- To determine what an electric field looks like and its magnitude in different areas, you can use a test charge to see how it reacts to the field. You do not want your test charge to be too large because then it will affect the field.- The magnitude of an electric field depends on the size of the charge and the distance between the creating charge and the test charge.- An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some (usually small) distance.- An electric dipole is in the direction of negative to positive, and is equal to the charge multiplied by the distance separating the charges.- Charges interact with each other via the electric field. The field is the agent that exerts the force. This force is equal to the charge multiplied by the magnitude of the electric field.- An electric field exists at all points in space.- Electric field vectors show the field only at one point, which is the point at the tail of the vector.- Two major tools for calculating electric field are: field of a point charge and the principle of superposition.- For continuous distribution of charge, divide the charge into segments for which you already know the field, find the field of each segment, then find the sum of all the segments.- Electric force causes acceleration. Therefore, you can ofen find the electric field by observing how a particle reacts to the field then using kinematics to find its acceleration and setting it equal to the charge of the particle divided by the mass of the particle then multiplying that quantity by the field.Lecture 13- For a line of charge (charged rod), an important value that is included in these calculations is the linear charge density, which is the charge divided by the length of the rod.- The simplest situation for a line of charge is when the rod is positioned so that half of its length is above the y-axis and half is below. This situation is the simplest because the electric field in the y-direction cancels as equals zero.- If you are very close to a relatively large line of charge (distance is 1% or less of length), the line of charge can be modeled as an infinite line of charge.- For rings and disks, you may need to involve the quantity of surface area density when calculating electric field strength.- For an infinite plane, the electric field does not depend on the distance from the charge (which is an important note to remember).- A parallel plate capacitor is formed when two infinite planes are near each other and oriented in the same direction. The electric field is zero at every place except between the two planes. Between the two plates, there is a uniform electric field that varies only by surface area density.- For an infinite line of charge, the direction of the electric field is always perpendicular to the line. Similarly, for an infinite plane of charge, the electric field is perpendicular to theplane.- Calculating the electric field for a sphere of charge is essentially the same as for a point charge.Lecture 14- A positive charge will encounter a force that is in the same direction as the electric field. A negative charge will encounter a force in the opposite direction as the electric field.- Acceleration is constant for a particle in a uniform electric field and not constant for a particle in a non-uniform electric field. Therefore, you can only use kinematic equations when dealing with a uniform electric field because the equations don't apply to situations in which acceleration is not constant.- If an electron and proton are both placed in the same electric field, the proton will have a smaller acceleration because of its larger mass and thus will have a less altered trajectory.- Important note: the net force on a dipole in a uniform electric field is zero. However, there is a net torque, so the dipole will rotate.- The electric dipole moment points in the direction from negative to positive.Lecture 15- If you know the electric field, you can use Gauss's Law to find the charge distribution.- Remember: to write an equation as a dot product, both quantities must be vectors. This applies to calculating electric flux because surface area is not usually a vector.- For a surface in a uniform electric field, the electric flux is the magnitude of the electric field multiplied by the area of surface (if it is a flat surface and the direction