Physics Exam #1
Where is the image located in the case of an object placed at a distance do=2f to the left of a converging lens?
2f
With 2 molecules, there are how many possible states?
4
What type of engine is ideal and reversible?
A Carnot engine
True or False: It is possible to use a convex spherical mirror to produce an enlarged image
False
Q is positive if the system (loses/gains) heat
Gains
Identical point charges are fixed to diagonally opposite corners of a square. Where does a third point charge experience the greater force?
In one of the empty corners because if the point charge were located at the center of the square, then the net force would be zero because the two forces would have equal magnitudes and opposite directions
With more molecules, the possible states (increase/decrease) rapidly
Increase
Adding heat to a system ALWAYS (increases/decreases) its entropy
Increases
Which of the following is true regarding the coefficient of performance of a heat pump?
It must always be greater than one.
Two systems are in the same state if their __________ properties are the same
Macroscopic (Their microscopic properties, however, are not identical)
What variable does "input heat" correspond to?
Qh
The motion of light along a light ray is (reversible/irreversible)
Reversible
What's a corner reflector?
Several plane mirrors that reflect light parallel to the incident ray, no matter the incident angle Ex. A periscope
As you cool things, they get (slower/faster)
Slower
What focus sun rays to heat oil?
Solar collectors
What are 3 quantities used to describe systems?
Temperature, pressure, and volume
What does reversible mean?
That it must be possible to return both the system and surroundings to exactly the same states they were in before the process began Ex. Gas-filled balloon
What takes the excess heat not being used as work in a heat engine?
The cold reservoir
What are the image properties of a plane mirror?
The image is upright, the same size as the object, and appears to be the same distance behind the mirror that the object is in front of the mirror (virtual), but reversed right to left
An object is placed at a known distance in front of a mirror whose focal length is also known. You apply the mirror equation and find that the image distance is a negative number. This result tells you that __________
The image is virtual
What's the law of reflection?
The incident ray, the reflected ray, and the normal to the surface of the mirror all lie in the same plane. Furthermore, the angle of reflection is equal to the angle of incidence.
What's the first law of thermodynamics?
The increase in the thermal energy in a system equals the work done on the system and the amount of heat added to the system.
What's the cold reservoir for air conditioners?
The interior of the house (the space being cooled)
What's the total energy associated with all of the particles in a system?
The internal energy (U)
What's the hot reservoir for air conditioners?
The outside
Calculate the magnification of the image when an object is placed at a distance do=2f to the left of a converging lens. Is the image inverted or upright?
m = -1 (inverted)
When you start at a certain location and come back to that same point, then ∆U = ?
0
Two charged particles A and B are located near one another. Both the magnitude and direction of the force that particle A exerts on particle B is dependent on what?
1. The sign of charge B 2. The sign of charge A 3. The distance between A and B 3. The magnitude of the charge on B
Consider the following four possibilities for two point charges and choose the one(s) that do not change the magnitude of the electrostatic force that each charge exerts on the other: A. Double the magnitude of each charge and double the separation between them B. Double the magnitude of each charge and reduce the separation between them to half of its initial value C. Double the magnitude of only one charge and double the separation between the charges D. Double the magnitude of only one charge and increase the separation between the charges by a factor of √2
A and D
What's a heat engine?
A device that converts heat into work; has a high-temp reservoir, low-temp reservoir, and cyclical engine Ex. A steam engine
What's entropy in microscopic terms?
A measure of the amount of disorder or randomness in a system
In order for the heat engine to run, there must be what?
A temperature difference (allows for heat transfer)
Where is a virtual mirror image located?
Behind the mirror
What's the range of COP values for refrigerators?
Between 2 and 6
Refrigerators, air conditioners, and heat pumps all use work to transfer heat from a _______ object to a _______ object
Cold; Hot
Car headlights always have a __________ mirror behind their light source
Concave
The front of a spoon is what type of mirror?
Concave
The back of a spoon is what type of mirror?
Convex
A kitchen air conditioner and a refrigerator both remove heat from a cold reservoir and deposit it in a hot reservoir. However, the air conditioner ____________ the kitchen, while the refrigerator _________ the kitchen
Cools; Warms The air conditioner cools the air in the kitchen and heats the air outside the house. When used properly, the refrigerator cools the air in its interior and warms the air in the kitchen.
Two positive point charges Q and 2Q are separated by a distance R. If the charge Q experiences a force of magnitude F when the separation is R, what is the magnitude of the force on the charge 2Q when the separation is 2R ?
F/4
What's the parallel ray for a concave mirror?
Goes from the tip of the object parallel to the axis and reflects through the focal point
What's the central ray for a concave mirror?
Goes from the tip of the object through the center of curvature of the mirror
What's the focal ray for a concave mirror?
Goes from the tip of the object through the focal point and reflects parallel to the axis
The focal point F of a concave mirror is where?
Halfway between the center of curvature C and the mirror at point B
What's convection?
Head transfer via air flow
What's the second law of thermodynamics?
Heat cannot flow from a colder to a hotter temperature unless work is done, and that heat cannot be converted completely into work.
Heat is spontaneous energy flow from a ___________ object to a __________ object
Hotter; Colder
What's the 0th law of thermodynamics?
If 2 systems, A and B, are both in thermal equilibrium with a 3rd system, then A and B are in equilibrium with each other Essentially, the transitive property
What's Carnot's theorem?
If an engine operating between 2 constant-temperature reservoirs is to have maximum efficiency, it must be an engine in which all processes are reversible
What's the 3rd law of thermodynamics?
It is impossible to lower the temp of an object to absolute zero in a finite number of steps (ie. you need an infinite number of steps to reach it)
A small puddle of water on a hot summer day could spontaneously reject heat into the environment, thereby cooling itself, so that it could solidify into ice? Why does this never happen?
It would violate the 2nd law of thermodynamics (heat cannot flow from a colder to a hotter temperature unless work is done)
For an ideal monatomic gas system, all the internal energy resides in the (KE/PE) of the particles
KE
Increasing the temperature of a gas or liquid increases the (KE/PE) of the molecules and (increases/decreases) the amount of disorder
KE; Increases
If a system is doing work on the environment, then it's (losing/gaining) energy to the environment, thus ∆U is negative. But the environment is (losing/gaining) energy, so ∆U(enviro) is positive
Losing; Gaining
What's a spherical mirror?
One in which the surface of the mirror forms a section of a spherical shell Ex. concave or convex mirrors
What's the study of light called?
Optics
Spherical wave fronts expand (outward/inward) at wave speed v
Outward
If the question asks how much heat is "expelled" which Q is it referring to?
Qc
What's the symbol for waste heat?
Qc
What's diffuse reflection?
Reflection from a rough surface
What's specular reflection?
Reflection from a smooth surface
A spherical mirror and a lens are immersed in water. Compared to the way they work in air, which one do you expect will be more affected by the water?
Since the angle of refraction depends on the index of refraction and the angle of reflection does not depend on the index of refraction, the lens will be more affected because the index of refraction of air is not equal to the index of refraction of water.
What are macroscopic quantities?
Systems of many particles
Internal energy is only ______________-dependent
Temperature
What determines the way heat flows between systems?
Temperature
What law of thermodynamics declares that a property called temperature exists?
The 0th law
A heat engine takes heat QH from a hot reservoir and uses part of this energy to perform work W. Assuming that QH cannot be changed, how can the efficiency of the engine be improved?
The conservation of energy states that Qh = W + Qc. If Qh is constant and W increases, the heat Qc must decrease.
Two identical containers, one filled with water (n = 1.33) and the other with benzene (n = 1.50) are viewed from directly above. Which container (if either) appears to have a greater depth of fluid?
The container filled with water will appear to have the greater depth because the index of refraction of water is smaller than the index of redraction of benzene.
Wave front surfaces are determined by what?
The crests and troughs of the waves
F of electric charges is indirectly proportional to what?
The distance between the charges; the smaller the distance, the higher the force
A heat engine takes heat QH from a hot reservoir, performs a certain amount of work W, and rejects the remainder QC of the heat to a cold reservoir. If QH and QC are doubled, what happens to the efficiency of the engine?
The efficiency does not change The efficiency e of a heat engine depends on the ratio QC/QH through the relation e = 1 - QC/QH . Doubling QC and QH does not change this ratio.
What's the larger system referred to as?
The environment
Rays that are parallel and near the principal axis of a concave mirror converge where?
The focal point after reflecting from the mirror
A refrigerator operates for a certain time, and the work done by the electrical energy during this time is W = 1000 J. What can be said about the heat delivered to the room containing the refrigerator?
The heat delivered to the room is greater than 1000 J The refrigerator uses the work W done by the electrical energy to remove heat QC from its interior and deposit heat QH into the room. In accordance with the conservation of energy, QH = QC + W. Therefore, the heat delivered into the room is greater than the electrical energy used to produce the work
What's ray tracing?
The method following the individual rays as they travel from an object to some other point
The focal length of the mirror is equal to what when the object is located very far away from the mirror?
The negative image distance
Two positively charged particles are separated by a distance r. The force on particle 1 is F due to particle 2. The force on particle 2 is 2F due to particle 1. Is the previous sentence true or false? Explain why this is the case.
The sentence is false because the forces on each of the two objects are equal in magnitude, as well as opposite in direction
The perpendicular distance between 2 wave fronts is prop to what?
The speed of light in that medium
What's heat (Q)?
The transfer of energy due to temperature difference
What's conduction?
The transfer of heat between 2 touching objects
The distance between wave fronts is proportional to what?
The wave speed
When your eye combines the rays to form an image, your brain extrapolates the rays back to where?
Their origin
Material B has the smaller refractive index. Therefore, a light ray that begins in material B and travels toward material A, with its greater refractive index, is bent (toward the normal/away from it) when it crosses the interface
Toward the normal
(T/F) All processes we discuss are quasi-static, meaning that they're slow enough that the system is always in equilibrium
True
(T/F) All reversible engines operating between the same 2 temperatures, Tc and Th, have the same efficiency
True
(T/F) Any ray that leaves the object and reflects from the mirror can be used in the method of ray tracing to locate the image
True
(T/F) If things are touching, at some point they're going to be the same temperature
True
(T/F) Letters and words held up to a mirror are reversed left-to-right and right to-left.
True
(T/F) Light is an electromagnetic wave
True
(T/F) The efficiency of a Carnot engine can NOT be 1.00 or 100%
True
(T/F) The process of photosynthesis is similar to a heat engine
True
(T/F) You can NEVER write "e" as a percent, it must always be written as a decimal
True
True or False: A heat engine is any device that uses heat to perform work. Heat is applied to the engine from a high temperature hot reservoir and rejected to a lower temperature cold reservoir
True
What is the given value for work in the statement: "A reversible heat pump operating between 2 thermal reservoirs consumes 500 J of energy each second."
W = 500 J
Keeping the refrigerator door open results in the kitchen becoming (warmer/cooler)
Warmer
What's reflection?
When a ray of light hits a surface and bounces off
On a summer day a window AC unit cycles on and off, according to how the temperature within the room changes. When will the outside of the AC unit be as hot as possible?
When the unit is on
If a clock is held in front of a mirror, its image is reversed left to right. From the point of view of a person looking into the mirror, does the image of the second hand rotate in the reversed (counterclockwise) direction?
Yes
The Zeroth Law of Thermodynamics deals with which of the following? a) Thermal Equilibrium b) Rotational dynamics c) Radiation d) Work and Energy
a) Thermal Equilibrium
Which of the following is true concerning two systems, A and B, which are both in thermal equilibrium with system C? a) If A and B are put into thermal contact, no heat will flow between them. b) If A and C are put into thermal contact, no heat will flow between them. c) If B and C are put into thermal contact, no heat will flow between them. d) All of the above
d) All of the above
