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# Physics

## Part II: Sections VI-X (334 Pages; 2018 Edition)

#### (Emphasis is on electrostatics and magnetism, electricity and circuits, sound and doppler effect, light and radiation, and geometrical optics.)

At the beginning of each of the 10 sections in the Physics Review Books is a page listing the "Selected equations, facts, concepts, and shortcuts" for that particular section. After reading the text in each section and completing the accompanying MCAT-style passages, we feel that you will have a better conceptual understanding of the material important to the physics found in the Chemical and Physical Foundations of Biological Systems section of the MCAT.

#### Section Goals

1. Know the difference between conductors and insulators. Conductors allow for the movement of charge while insulators impede the movement of charge.

2. Understand how to use Coulomb's law. Be aware that this law applies only to charges in a vacuum. Be familiar with the unit of charge, the coulomb, and how charges interact with one another.

3. Understand how electric fields are created. An electric field can be defined as the ability of a charged particle to exert a force on another charged particle. Know how to use a positive test charge to probe an electric field.

4. Be familiar with field lines and know how to draw them. Electric field lines are defined to show the direction of the electric force that acts on a positive test charge. They will never intersect with one another.

5. Understand the meaning of the dielectric constant. The effect that a medium can have on charges is taken into account by a parameter called the dielectric constant. This parameter is just the ratio of the electrical force between two charges when they are in a vacuum compared to when they are in a given medium.

6. Understand the meaning of electrostatic potential and how it is related to electric potential energy and electric field. Electrostatic potential can be defined as the ability of a charged particle to do work on another charged particle. If a test charge is moved from one place to another against an electric field, the test charge experiences a change in electrostatic potential. The work done against the electric field is converted to electrostatic potential energy.

7. Be familiar with equipotential lines. An equipotential line is simply a surface on which the potential is the same everywhere. Understand what happens to a test charge when placed at any point on the same equipotential line.

8. Be familiar with electric dipoles. An electric dipole can be established if two charges of opposite sign are separated from one another by some distance. Understand what happens if a dipole is placed in a uniform electric field. Understand what happens when the torque is at a maximum or a minimum.

9. Be familiar with magnetic fields. Magnetic fields have a magnitude and they have a direction. Magnetic fields can exert a magnetic force on a charge moving in that field. The moving charge will feel a force which is always perpendicular to both the velocity and the magnetic field.

10. Be familiar with the electromagnetic spectrum. Electromagnetic waves are electrical and magnetic disturbances that propagate through space at the speed of light. Know the speed of light. All of the different types of electromagnetic waves have a characteristic wavelength and frequency that can be related to the speed of light. Understand how to use this relationship.

#### Passages and Solutions

Section VI includes 6 MCAT-style passages with detailed solutions. Passage topics are centered around information important to electrostatics and magnetism.

#### Section Goals

1. Be familiar with electric currents. The flow of charge (q) from one point to another point during a certain amount of time (t) is called an electric current (I) and can be defined by the expression I = delta q/delta t. Current has a direction in an electric field. Current flows in the same direction that positive charges will flow and in the opposite direction that negative charges will flow.

2. Be familiar with batteries and how they operate. Batteries are an important source of electric power. They have a negatively charged pole (anode) and a positively charged pole (cathode) that allows for a separation of charge. Movement of this charge from a low potential to a high potential generates an electromotive force (a voltage source).

3. Know how to use the expressions for resistivity and conductivity. The resistivity of a material is the ratio of the electric field to the current density. Conductivity is just the reciprocal of the resistivity.

4. Understand how to use Ohm's law. Ohm's law is a relationship between the current (I) in a conductor, the electrical resistance (R) in a conductor, and the potential difference (V) across the ends of a conductor. The expression for Ohm's law (V = IR) is a direct result of the proportionality between the electric field and the current density.

5. Be familiar with electric power. Power is the rate of conversion of electrical potential energy into some other type of energy. Know how to relate power to current and voltage.

6. Know how to apply Kirchhoff's loop rule and Kirchhoff's junction rule. Kirchhoff's loop rule states that the algebraic sum of the potential differences (voltage changes) in any closed circuit (loop) is equal to zero. Kirchhoff's junction rule states that current flowing through a junction must equal the current that entered the junction. Be sure you understand how to use these two rules.

7. Know how to work with resistors in series and in parallel. Understand how to replace several resistors in series with a single equivalent resistor and how to replace several resistors in parallel with a single equivalent resistor.

8. Be familiar with capacitors and dielectrics. A capacitor is formed from two conductors which are separated by an insulator. Understand what happens when a voltage is placed between the parallel plates of a capacitor. Know how to calculate the capacitance of a capacitor. A dielectric is a non-conducting material between the conducting plates of a capacitor.

9. Understand the process behind charging a capacitor. An emf source such as a battery can be used to charge a capacitor. Know what happens as more and more positive charge flows to the positively charged plate of a capacitor. Be able to predict what the charge on the capacitor and the voltage drop across the capacitor will be at various times after the capacitor begins charging or discharging.

10. Know how to work with capacitors in series and in parallel. Be aware that the form of the expression for working with capacitors in series and in parallel is different from the form of the expression for working with resistors in series and in parallel.

#### Passages and Solutions

Section VII includes 6 MCAT-style passages with detailed solutions. Passage topics are centered around information important to electricity and circuits.

#### Section Goals

1. Have a general understanding of how the human ear detects sounds. Be familiar with the basic anatomy of the human ear. Be able to outline the steps involved in conversion of a sound wave to a nerve impulse.

2. Be familiar with the mechanics of a sound wave. As a sound wave moves forward, it will begin to compress the medium in front of it, resulting in a compressional waves moving outward in all directions from the source of the sound.

3. Know how to find the speed of a longitudinal sound wave in various media. Have a feel for the speed of sound in air. Be aware that the speed of sound in liquids and metal is much higher. Understand why this is the case.

4. Be familiar with the subjective properties used to describe sound. Know the difference between pitch and intensity. Pitch describes the frequency of a sound. The intensity of a sound wave is the power that the wave transports per unit area of its wave front.

5. Know the difference between the intensity and intensity level of a sound. The units for sound intensity is expressed watt/m2. The units for sound intensity level is expressed in decibels.

6. Understand what is meant by the Doppler effect. The Doppler effect can be exhibited by all types of waves. The Doppler effect is a frequency shift that occurs because of motion of the source of the wave, or motion of the receiver of the wave or motion of both source and receiver.

7. Know the general form of the Doppler equation and how to use it. Have a good understanding of each variable in this equation. Know why if you are moving toward the source of a sound, the frequency of sound waves encountered by the listener will always be greater than the frequency of sound waves emitted by the source. Conversely, know why if you and the source of the sound are moving away from one another, the frequency of the sound waves encountered by the listener will always be less than the frequency of the sound waves emitted by the source.

8. Be aware that the Doppler shift for light waves differs than that for sound waves. Sound waves need a medium in which to propagate; light waves do not. In space one can only say that an observer and a source of light are moving with respect to one another. This is based on Einstein's principle of relativity.

9. Be familiar with resonance in strings. Understand the nature of a standing wave, a node, and an antinode. Know how far nodes are away from one another. Know where an antinode is in relation to a node.

10. Be familiar with resonance in closed and open pipes. Understand how a pressure pulse of air moves into and out of a closed pipe and an open pipe, and how it undergoes a change of phase. Understand why a closed pipe can vibrate at odd multiples of the fundamental frequency and not at even multiples. Understand why an open pipe can vibrate at all fundamental frequencies.

#### Passages and Solutions

Section VIII includes 6 MCAT-style passages with detailed solutions. Passage topics are centered around information important to sound and doppler effect.

#### Section Goals

1. Review the electromagnetic spectrum (again). Know where the major electromagnetic waves fall within the electromagnetic spectrum. Know where the wavelength of visible light begins and where it ends in this spectrum. Know the colors associated with those wavelengths.

2. Know the difference between unpolarized and polarized light. Light that radiates in all planes is said to be unpolarized. If light were to be passed through a polarizing filter, then radiation would occur in just one plane, and the light would be linearly polarized. Understand how this occurs.

#### Passages and Solutions

Section IX includes 6 MCAT-style passages with detailed solutions. Passage topics are centered around information important to light and radiation.

#### Section Goals

1. Understand the law of reflection. The law of reflection says that the angle an incident light ray makes with a surface is equal to the angle that the reflected light ray makes with the surface.

2. Be familiar with the index of refraction. If a light wave passes from one medium to another, its direction usually changes. The wave that changes direction is said to be refracted. Refraction is the result in the change of speed of the incident light wave as it passes from one medium to the next. Electromagnetic radiation that passes through a vacuum travels at the speed of light. However, in a medium other than a vacuum the velocity of the wave depends on the medium itself. The index of refraction is the ratio of the speed of a wave in a vacuum to the speed of that wave in a given medium.

3. Understand how to apply Snell's law. The relationship between the index of refraction of each medium and the angle of incidence and the angle of refraction is governed by Snell's law.

4. Be familiar with total internal reflection. When light rays from an underwater light source reach the surface of the water, some are reflected and some are refracted. However, as the angle of incidence increases, the intensity of the refracted rays decreases while the intensity of the reflected rays increases. At some critical angle of incidence there is total internal reflection.

5. Be familiar with the phenomenon of dispersion. Understand why red light is deflected the least while violet light is deflected the most as white light is passed through a prism.

6. Know how to work with lenses. Two types of lenses to be familiar with are converging lenses and diverging lenses. Understand what is meant by a focal point, a real image, and a virtual image. Know how to use the expression for a thin lens. Be familiar with the linear magnification of an object.

7. Be familiar with combination lenses. Optical instruments like binoculars, telescopes, and microscopes contain more than one lens. Understand how they work.

8. Be familiar with mirrors. Mirrors focus light by reflecting it. The three general types of mirrors are plane (flat), concave (converging), and convex (diverging). Know how to use the thin lens expression for locating an image produced by a mirror.

#### Passages and Solutions

Section X includes 6 MCAT-style passages with detailed solutions. Passage topics are centered around information important to geometrical optics.

#### Five Diagnostics

At the end of Book II are five diagnostics, each with 9 passages, free standing questions, and detailed solutions.

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