Introduction to Physical Science/A.2

=Practice Problems Exam 2= '''Dear Users - please note students are currently working on these problem sets - please do not edit until their signature tag has been removed --J.M.Pearce (talk) 23:25, 3 April 2008 (UTC)

Students - please put in two questions for the review and work out entire example. Put your answers in boxes by putting a space before it. Make sure to include all equations and units. Make sure to tag your question with --~

Thank you.

Waves
Wave Speed = wavelength * frequency 340m/s/2.43m = 139.91Hz
 * A Sound wave from a tuning fork moves at 340 m/s. It has a wave length of 2.43m. What is it's frequency?


 * Name, and describe two types of waves that we discussed in class.

Transverse Wave: motion of the particle is perpendicular to the direction of the wave Longitudinal Wave: motion of the particle move the same direction


 * A wave is traveling with a frequency of 70.0 Hz and has a wavelength of 50 m. What is the speed of this wave?

velocity= wavelength X frequency velocity= 50 m X 70.0 Hz velocity= 3500 m/s


 * As a wave moves, intensity _________ with distance, and ________ as it passes through a material.

Intensity DECREASES with distance, and DECREASES as it passes through a materal.

Any Pattern with an indentifable periodicity in space and time. No matter is transferred but energy is.
 * What is the definition of a wave?


 * A wave has a wavelength of 70m and a frequency of 80Hz. How fast would this particular wave be traveling?

= Wavelength x frequency = 70m x 80HZ = 5600m/s


 * Illustrate diffraction

At a time(t) consider everypoint on a wave front, a new point source.
 * Illustrate Hugen's Principle?

crest and trough
 * What are the names for the highest and lowest points of a wave?

Sound
1. For sound waves, as the _________ of a material increases, _________ increases

Density and Velocity 2. Dolphins can hear noises at the frequency of 250 kHz. If a dolphin hears a sound with this frequency that is moving with a velocity of 1700 m/s what is it's wavelength?

Use the equation v=λf, for this problem it is v/f=λ. First convert 250kHz to 250000Hz. 1700m/s divided by 250000Hz = 6.8x10^3m

3. Sound cannot travel through a vacume because it needs what?

Sound needs a medium to travel through. (solid, liquid, or gas)

4. What is Refraction when dealing with sound waves?

An abrupt change in wave speed at boundary of two mediums.

5. What is the equation for Refraction?

f = v1/wavelength = v2/wavelength2

Electromagnetic Waves
Radio waves, microwave, infrared, visible, ultraviolet, x-ray, and gamma rays.
 * What are the seven type of waves in the electromagnetic spectrum in order of their size (largest to smallest)?

The periodic oscillations in the electric and magnetic components.
 * The wave-like properties of electromagnetic radiation are due to what?

Wavelength=velocity / Frequency 3.8m/s x 15s= 57m/s(squared)
 * 1) If a wave is traveling at a velocity of 3.8m/s and the end of the wave reaches where the fron t of the wave started in 15s.


 * If an AM radio wave has a length of 300 m, what is it's frequency?

Frequency = speed of light (c) / wave length Frequncy= (3 x 10^8 m/s)/ 300 m Frequency= 1 x 10^7 Hz

c is constant. c=3x10^8 m/s legth=c/f=3x10^8/1.5x10^7Hz=20m
 * An electromagnetic wave has a frequency of 1.5x10^7 Hz, what is the lenth of the wave?

Light
A convex mirror curves away from you and a concave mirror curves toward the viewer.
 * What's the difference between a convex mirror and a concave mirror?


 * What can the size of an infrared light wave be compared to physically? (e.g. a bread box, an atom, etc).

a pinhead

Reflection
1. A beam of light is sitting in the floor 45 degree and it is shining to a mirror that was sitting at the floor 90 degree, if the mirror turn 45 degree where the light is pointing to and the light remain the same position, what will be the new reflection angle? (Hint: follow the wording use the diagram only as a guide)

No reflection will occour because the mirror and the light become parallel.

Refraction
Empty

CFL
Answer: 25%
 * A Compact Fluorescent Light bulb (or CFL) uses roughly ____ percentage of the electrical wattage needed for an incandescent light bulb to produce the same amount of light.

Answer: True
 * True or false  CFL's are a more economical choice over the standard incandescent bulbs

Answer: 20 x 32 $640
 * If a house has 20 light fixtures and they switch to CFL's, that save $32 per bulb, how much will the household save?


 * CFL Bulbs that have the equivalent power of a 60 Watt Incandescent bulb have ____ watts.

Answer: 15 watts


 * If you have 10 fixtures to replace with CFL light bulbs and the total costs over 8,000 hrs of illumination at Clarion rate of $0.0615 per kW-hr are$18.30 per fixture. How much will your initial costs be to replace the light bulbs with the energy saving bulbs?

Answer: $18.30*10=$183 as your initial cost for CFL bulbs

Answer: CFL's use mercury vapor and when the mercury vapor is exposed to an electrical current the electrons begin to move quickly, emitting light. An Incandescent light bulb uses a filament which emits mostly heat, which makes it   much less efficient.
 * How do CFL light bulbs differ from incandescent light bulbs?


 * If a CFL light bulb has a pay back time of 5.4 months and you save 1.12 per month and the life time is 3 years, what is your total return on investment?

Answers: 36 months - 5.4 = 31.6 months x $1.12 = $35.40

LEDs
Nothing

Energy

 * What is the formula for electrical energy?

Answer: Energy=Power(Time)

Light, chemical, electrical, lastic, nuclear, sound, thermal, gravitational.
 * Name 5 forms of energy

E=Pt = [w][hrs] 1000w=1kw =3(5)     =15kw*hr
 * How much energy is being used while using 3000 watts for 5 hours?

E=Pt =(500w)(8hrs) = 4,000w-hrs = 4kw-hr E= 4kw-hr
 * If you use one electrical space heater at 500w to heat your living room for 8 hrs. How much energy does it use in kw-hr? 1000w= 1kw-hr


 * What are 3 examples of chemical energy?

Gasoline, fossil fuels, batteries


 * Can energy be lost when it is used in a particular task?

no, energy can only be transfered from on form to another--Natehepler

.12[kw-hrs]
 * A 120 watt curling iron plugged in for 1 hour uses how much electrical energy?

1000
 * How many watts are in a kilowatt?

11. A force of 6 N is moving a box over a distance of 2 meters. How much work is being exerted on the object? w=6x2; w=12J

Temperature
Thermodynamic Equilibrium
 * When dealing with science, equal temperatures are also known as this term?

373-273=100
 * The boiling point of water in degrees Kelvin is 373. Find the boiling point of water in degrees Celsius.


 * If you have a temperature of 63 degrees Celcius, what would that same temperature be in Kelvin?

Formula: T Kelvin = T Celcius + 273 T Kelvin = 63 + 273 T = 336


 * What is Thermal Expansion and what causes it to occur?

Answer: Thermal Expansion is the expansion/contraction of a material due to temperature change. When most materials are heated, the atoms move faster and cause the material to expand; the opposite occurs when it is cooled. Thermal expansion is calculated by using a "coefficient of thermal expansion" specific to that material, since the expansion/contraction of each material varies.


 * A 10-inch long copper rod is heated from 70°F to 180°F. The coefficient of thermal expansion of copper is 9.3×10^-6 in./°F.  What is the length of the rod after it has been heated?

ΔL = α×L×ΔT Where α=coefficient, L=original length, ΔT=change in Temperature ΔL=(9.3×10^-6)(10 inches)(180-70°F) ΔL=(9.3×10^-6)(1100 in./°F) ΔL=(0.01 inches) 10 inches + 0.01 inches = 10.01 inches

Heat Transfer
ways?
 * How many ways can heat be transfered and what are the specific

-3 -Conduction -Convection -Radiation

is 90cm x 60 cm. The glass in the window is .35 cm thick. The temp outside is 5 c and inside it's 20 c. What is the rate of heat loss through your window? Remember K= .63 w/mk
 * Lets say you have a wall with a window in the middle. The window

Icd=Q/t=KAΔT/d

.63w/mk(90x10 raised to the negative 2)(60x10 raised to the -2)(20-5) divided by .35x 10 raised to the negative 2 m

the answer is 1458 w


 * 1) Jimmy is replacing the 17ft x 14ft window in his kitchen. The glass he purchased is 0.34cm thick. The current temperature in Jimmy's house is 23 degrees Celsius and the temperature outside is 7 degrees Celsius. K is 0.63w/mK. What is the thermal gradiant?

Solution: ΔT/d Change in temp= 23-7 =16.0 D = 0.34 ΔT/d = 16/0.34 = 47.06

It is the thermal gradient.
 * What is ΔT/d?

T=21.1-10=11.1 D=0.42     ΔT/d.... 11.1/.42= 26.4
 * The Jones are getting new window for in their living room. They are 50cm x 45 cm. The glass is 0.42 cm. The outside temperature is 10°C, the inside is 21.1°C. K is 0.63w/mK. What is the thermal gradient?


 * Name the 3 types of heat transfer.

Conduction, Convection, and Radiation

the glass is .32cm outside temp. is -15°C inside temp. is 22°C and K is 0.63w/mK. Using this information what is the Thermal gradient?
 * We are getting new windows in the classroom.From the example we had in class 20cm x 15cm,

ΔT/d 22-(-15)= 37 d=.32 37/.32= 115.62

A. Having multiple panes B. Use an inert gas--vacuum C. Low conductivity spacers, either plastic or wood D. Having a single pane E. Low e coating
 * All of the following are ways to improve windows except:

D is the correct answer. Icd=KA(change in temp)/d Plug in the numbers and the answer is 368 W. Conduction-a collision of molecules Convection- energy transfer by movement of material (forced air) Radiation-energy transfer with electromagnetic waves
 * What is the rate of heat loss thru a 30 cm by 25 cm single pane window, with a thickness of 0.45 cm thick, when it is -10 degrees C outside and 25 degree C inside. If given K=0.63 W/mK, what is the rate of loss?
 * Describe the 3 different types of heat transfer.

Icv=(h)(A)(change in temperature) Icv=(32)(1.2m2)(6 degrees celcius) Icv=230.4 W
 * A baseball player has a surface area of 1.2m2 with a skin temperature of 34 degrees celcius. He is standing in center field. The air temperature is 28 degrees celcius and the wind velocity is 4m/s. The coefficient of convection is 32. Icv=?

the windspeed is 3m/s, and the sailors skin temp is 30°c. What is the Icv? ( h=26)                                                            -
 * A shipwrecked sailor is lying on a beach. The sailors skin area is 1.8m², the air temp is 25°c,

use the formula Icv = hAΔT = 26(1.8m²)(30 - 25) = 234w

-Use the formula Icv=(h)(a)(change in temperature) Plug in the numbers in the correct places. Icv= (37)(1.6 m2) (45-35) iCV= (37)(1.6 m2) (10) Icv=592 w
 * A hockey player has a surface area of 1.6 m2 with a skin temperature of 35 degrees celcius while he is warming up for a big game. The temperature in the arena is 45 degrees celcius and there is a slight breeze from the top being open and it is 2 m/s.  What is the  Icv? (h=37)

Radiation
 * 1) Which form of heat transfer involves electromagnetic waves?

Hot to cold
 * Temperature moves from a___________object to a____________object until the temperatures of both objects are equal.

Thermodynamics

 * 1) What is the second law of Thermodynamics?

No refrigerator or heat pump can have an inefficiency of zero.


 * 1) What is the third law of Thermodynamics?

It is impossible to cool a system to absolute 0.

Heat Engines

 * A heat engine is rated as 85% efficient. If the heat input is 500W what is the work output to make the efficiency true?

E=work output/Q input .85=output/500W .85x500=425W output=425W

Refrigerators

 * The fridge in your kitchen has a heat output of 60 and work input of 250. What is the inefficiency of the refrigerator?

Answer: The answer is 4.2 The inefficienct of the fridge is ein = work input / heat output = 250 / 60                                                                =  4.2
 * The 2nd Law of Thermodynamics states what about refrigerators or heat pumps?

Answer: The 2nd Law of Thermodynamics states that No refrigerator or heat pump can have an efficiency of 0 (zero).


 * The 3rd law of thermodynamics states that it is impossible to cool a system to ________.

Absolute zero (or, 0 degrees Kelvin)

Heat pumps
inefficiency
 * 1) . The 2nd law of thermodynamics is no refrigerator or heat pump can have a(n) underline text of zero.

ein= work input/heat output work input= 100 x 6.5 work input= 650
 * 1) . You have an air conditioner which has a heat output of 100 and an inefficiency of 6.5. What is the work input?

Microturbines
What is a Microturbine?

A Small Electric generation systems based on turbine technology.

If you put 100 units in how many units will it produce out? 150 units?

85 units, it is 85% efficient 150 x .85= 85% ... 150 x .85= 127.5 units


 * What does the 1st law of thermodynamics deal with?

Energy conservation


 * What is 2 of the 5 ways one can improve windows?

Multiple layers of glass, no frames of metal, insulate frames, fill glass with inert     gas,Low emissivity coating