Study Questions for Final Exam

Physics 106N - How Things Work - Spring, 1997

Section 1.1 - Falling Balls

What is the difference between velocity and acceleration?
What is the difference between weight and mass?
How does an object’s mass affect its acceleration?
What forces are acting on a freely falling object as it heads upward; as it heads downward?
Why do all freely falling objects accelerate downward at the same rate?
Why doesn’t the horizontal component of an object’s velocity change as that object falls?

Section 1.2 - Ramps

Which object experiences each force when the two objects push against one another?
What must you do to an object to do work on it?
What is the relationship between work and energy?
Why does an object’s gravitational potential energy increase as its altitude increases?
When a object slides freely on a ramp, what is the direction of the net force on that object?
How does employing mechanical advantage to perform a task affect the work you do?

Section 1.3 - Seesaws

What is the difference between angular velocity and angular acceleration?
What effect does a torque have on an isolated object?
About what point does an isolated object rotate?
How can you use a force to produce a torque?
How can you use a torque to produce a force?
How does an object’s moment of inertia affect its angular acceleration?
Why must two objects be on opposite sides of a seesaw to balance one another?

Section 1.4 - Wheels

How do the two types of friction, static and sliding, differ from one another?
How can sliding friction bring a moving object to rest without violating the conservation of energy?
Why does the wheel of a toy wagon begin to turn when you pull that wagon forward?
Why does an automobile accelerate forward when the engine begins to turn its wheels?
What is the difference between force and momentum?
When you throw a baseball forward, where does the ball’s momentum come from?
When you spin a toy top, where does the top’s angular momentum come from?

Section 11.1 - Electronic Air Cleaners

Why do tiny particles descend so slowly through the air?
How do the forces between two electric charges depend on the types of charges and on their separation?
Where is the charge located on an electrically charged metal object?
Why are thin wires or sharp points so effective for transferring charge to the air or to dust particles in the air?
What holds an electrically charged balloon against the wall?

Section 11.2 - Xerographic Copiers

Why don’t all the electrons in a solid travel in the lowest energy level?
How do an insulator and a conductor differ?
What role does electric field play in the force that one electric charge exerts on another electric charge?
How does light exposure cause a semiconductor to transform from an insulator to a conductor?

Section 11.3 - Magnetically Levitated Trains

How do the forces between two magnetic poles depend on the types of poles and on their separation?
What is the net magnetic pole of a grapefruit?
What role does magnetic field play in the force that one magnetic pole exerts on another magnetic pole?
How can an electric charge produce a magnetic field?
How can a magnet produce an electric field?
What can you do to piece of aluminum to make it become magnetic without touching that aluminum?
Why does an electric current that’s flowing on its own through a copper ring gradually diminish as time passes?
Why does an electric current that’s flowing on its own through a superconducting ring continue to flow steadily as time passes?

Section 12.1 - Flashlights

Why must there be a complete electric circuit before current will flow steadily between a battery and a light bulb?
What is the difference between current and voltage?
What effect does a battery have on a current that flows through it?
Why is the direction in which current flows through a battery important?
How can two different electric currents, with different amounts of current and different voltages, deliver identical amounts of power to their respective light bulbs?
Why can a battery either provide or consume power, while a light bulb can only consume power from the circuit it’s in?

Section 12.2 - Electric Power Distribution

How does increasing the current through a wire affect the power wasted in that wire?
What becomes of the power wasted in a wire?
How can two different currents in two identical wires deliver equal amounts of electric power to their destinations while wasting different amounts of power in those wires?
How does a transformer transfer power from one circuit to another without allowing any charges to pass between those circuits?
Why do a transformer only work with alternating current?

Section 12.3 - Electric Power Generation

How does moving a magnetic past a coil of wire affect the current passing through that coil?
Why does an electric generator need something to keep it turning, even if its bearings are essentially frictionless?
How does the energy stored in a fossil fuel reach your home electrically? What forms does it take along the way and how is it transferred or transformed as it moves along?
How does a diode prevent current from flowing through it in one direction?
How does light allow a diode to provide electric power?

Section 12.4 - Electric Motors

What does the rotor of a motor continue to turn indefinitely?
Why does an electric motor powered by direct current need some sort of internal electric switch to keep turning?
How can the aluminum rotor of an induction motor experience magnetic forces even though aluminum is a non-magnetic metal and there are no electric connections to the rotor?
What determines the direction in which an induction motor rotates?

Section 12.5 - Tape Recorders

In what way is iron intrinsically magnetic?
Why does a large piece of iron normally appear non-magnetic?
How does the presence of a nearby magnetic pole cause a piece of iron to exhibit its intrinsic magnetism?
Why do some magnetic materials remain permanently magnetized?
How does the surface of a magnetic tape represent sound?

Section 13.1 - Audio Amplifiers

Why does an audio amplifier need a source of power?
Why is it important that the current an amplifier sends through its output circuit be proportional to the current passing through its input circuit?
How does the voltage drop a current experiences as it passes through an electric resistor depend on how well that resistor conducts electricity?
How does a capacitor store electrostatic potential energy without acquiring any net electric charge?
How does electric charge on the gate of an MOSFET control the flow of current between its source and drain?

Section 13.2 - Computers

How can electric charge represent a bit of information?
How can magnetism be used to represent information?
If two electronic components are connected in parallel to one another, how is the total current they’re carrying related to the current through each component?
If two electronic components are connected in series with one another, how is the total current they’re carrying related to the current through each component?
Why does a computer’s size affect the speed with which it can perform calculations?

Section 14.1 - Radio

Why does a tank circuit’s energy transform back and forth rhythmically between electrostatic potential energy and magnetic potential energy?
How does the movement of charge on one antenna affect the charge on another nearby antenna?
Why does an electromagnetic wave always have both an electric field and a magnetic field.
What produces the electric field in an electromagnetic wave?
What produces the magnetic field in an electromagnetic wave?
How does a radio station use amplitude modulation to instruct a radio receiver what to do with its speaker?
How does a radio station use frequency modulation to instruct a radio receiver what to do with its speaker?

Section 14.2 - Television

How does electric current flow between the back of a picture tube and its front surface?
How does electric energy become light energy in a television?
How does a magnetic field affect a moving electric charge?
How is a television image constructed on its screen?

Section 14.3 - Microwave Ovens

What distinguishes microwaves from radio waves and visible light?
How do metals reflect electromagnetic waves?
Why does water become hot when exposed to microwaves?
How does a C-shaped piece of metal act as a microwave tank circuit?
Why is the antenna in a microwave oven only a few centimeters long?

Section 15.1 - Sunlight

How does a hot surface produce light?
Why does light slow down when it enters matter?
Why does the surface of a transparent material partially reflect light?
Which way does light bend when it enters the surface of a transparent material?
Why does white light separate into colors after going through cut crystal or a diamond?
Why does a thin transparent film often appear colored?
Why do many good sunglasses block horizontally polarized light?

Section 15.2 - Fluorescent Lamps

Why are red, green, and blue the primary colors of light?
Why is incandescent light energy inefficient?
Why must the electrodes of a typical fluorescent lamp be hot in order to sustain the electric discharge in the mercury gas?
What determines which wavelengths of light are emitted by a low pressure gas discharge?
How does high pressure in a gas discharge affect the wavelengths it emits?

Section 15.3 - Lasers

How does coherent light differ from incoherent light?
How does a laser produce coherent light?
What does it mean to amplify light?
Why does a laser oscillator need several mirrors to operate?
Why does a laser need a great many identical excited atomic or atomic-like systems to operate?
How do some lasers store energy and then produce incredibly bright pulses of light?

Section 16.1 - Cameras

Why does the distance from an object to a converging lens affect the distance from that lens to the real image it forms?
Why is a real image only formed at a specific distance from a converging lens?
How does the focal length of a converging lens affect the distance from it to the real image it forms?
Why does a small lens have a greater depth of focus than a large lens?
What color problems does a single element converging lens have?
What change occurs on a piece of photographic film when that film is exposed to light?

Section 16.2 - Telescopes and Microscopes

When you use a converging lens as a magnifying glass, where is the image located?
What part does the objective of a telescope or microscope play in providing an enlarged view of the object you’re observing?
What part does the eyepiece of a telescope or microscope play in providing an enlarged view of the object you’re observing?
Why is a large-aperture telescope able to resolve finer details than a small-aperture telescope?

Section 16.3 - Compact Disc Players

Why is it important to use a laser rather than a conventional light source in a compact disc player?
Why is the wavelength of the laser light shorter inside the disc than in the air?
How does interference improve the player’s ability to distinguish ridges in the aluminum layer from valleys?
How does reversing the polarization of the laser light prevent it from returning to the laser diode?
Why do horizontally and vertically polarized lights bend differently when entering or exiting a birefringent crystal?
When does total internal reflection occur?

Section 17.1 - Knives and Steel

What is the relationship between stress and strain?
What happens inside a metal when you bend it gently and it then returns to its original shape when you let go?
What happens inside a metal when you bend it severely and it does not return to its original shape when you let go?
How does the inclusion of carbon in steel make it more difficult to deform that steel permanently?
Why does steel suddenly lose its magnetism when you heat it red hot?
How does the speed with which carbon steel is cooled affect its hardness?
Why can’t common stainless be hardened by carbon and heat treatment?

Section 17.2 - Windows and Glass

How are the atoms in a glass arranged differently than in a crystal?
How is a glass formed?
Why is quartz so good at forming glasses?
Why is tempered glass so difficult to break?

Section 17.3 - Plastics

What are the molecules in a plastic like?
Why do plastics always contain amorphous regions?
What sorts of molecular motions account for the five regimes of plastic behavior?
Why do only certain plastics melt?
How are plastics formed?
Why are plastics with straight polymer chains extremely strong?

Section 18.1 - Nuclear Weapons

In what sense do the two forces present in an atom’s nucleus oppose one another?
Why do large nuclei often release energy when they break in half?
Why is the short range character of the nuclear force essential to the existence of spontaneous fission?
Why is uranium-235 suitable for a fission bomb while uranium-238 is not?
Why is it so difficult to separate uranium-235 from uranium-238?
"Critical Mass" is a misnomer—what arrangement of materials is actually required for an explosive fission chain reaction to occur?
How does a fusion bomb differ from a fission bomb?

Section 18.2 - Nuclear Reactors

Why doesn’t a nuclear reactor explode the instant its core exceeds critical mass?
How do "control rods" keep a reactor’s chain reaction from getting too intense?
How can a thermal fission reactor operate on natural uranium?
How does a moderator slow neutrons down?
Why does a fast fission reactor require enriched uranium?