A sound wave is a ____________ kind of wave and a light wave is a __________ kind of wave.
Sound waves are Longitudinal; can also be thought of as mechanical or compression.
Light waves are Transverse waves.
100
Currents are moving electrons (e-) what is the symbol associated with current, and what are currents measured in?
Currents are represented with the symbol I and are measured in amperes (A)
100
The current in a 12 ohms (Ω) toaster is operated at 120 V is?
Voltage= Current x Resistance [V=IxR]
V= 120 V 120v = I x 12 -> 120/12= 10 A (I)
R= 12 ohms (Ω)
I= ?
200
What are the SI units for density?
SI units= kg/m^3 and g/cm^3
200
What are electromagnets and what are some examples?
Electromagnets uses an electric current for a possible magnetic object to pick things up and when turned off the things fall.
Examples: our fob door systems, the magnetic cranes at junk yards.
200
What are the different parts of a wave?
crest, through, amplitude, and wavelength
200
What are the two types of current, and what is an example of each?
Two types of current are:
- Alternating current (AC): the positive & negative polarities switch directions. ex= home wall outlets.
- Direct current (DC): the two terminals never switch polarities, one is always positive & one is always negative. ex= standard batteries.
200
a) If a 75-W light bulb is connected to a 120-V power line, how much current flows through it?
b) What is the resistance of the bulb?
c) How much power does the bulb consume?
a) P= I x V -> I= P/V
P= 75 W V= 120 V I= ?
75 W = I x 120 -> 75/120= 0.625 A
b) V=I x R -> R= V/I
V= 120 V I= 0.625 A R= ?
R= 120 V/0.625 A = 192 ohms
c) 75 W
300
What is the definition of density?
Density of a material is its mass per unit volume
300
What is the purpose of a transformer, and what kind of current do they use?
The purpose of a transformer is to raise or lower the amount of electrical current. Transformers us alternating current (AC) to allow the electricity to flow through other wise if it used direct current (DC) then it would become one big magnet and no electricity would move through.
300
How are frequency, wavelength, and energy related?
high frequency = high energy & low wavelength
low frequency = low energy & high wavelength
300
How is a current produced - in other words how do we make electrons move?
Electrons move by separation of charge (voltage) which in turn makes a current. The separation of charge allows a path for the electrons to move and over all making a charge.
300
Find the frequency of sound waves in air whose wavelength (λ) is 25 cm.
* Vsound = 343 m/s (this is a constant)
V= f/wavelength (λ)
V= 343 m/s V=f/λ
wavelength (λ)= 25 cm 343 m/s= f/ 25 cm
f= ? Hz 25 cm-> .25 m
343/.25 = 1372 Hz.
400
What is the relationship between pressure, temperature, and volume of a gas?
- Pressure vs. Volume: low Volume = high Pressure (inverse relationship)
- Volume vs. Temperature: high Volume = high Temp. (direct relationship)
- Pressure vs. Temperature: high Pressure = high Temp. (direct relationship)
400
How can magnets be used to create electrical current?
By moving a magnet through a conductor an electrical current is produced. Demo was done in class.
400
Sound waves require the necessary media of ____, _____, and _____ media; Light waves require the necessary media of _____, _____, ______, and _____.
Sound requires= solid, liquid, or a gas
Light requires= solid, liquid, gas, or vacuum.
400
What are the two types of circuits and what are is the difference between the two? What is and example of each type?
The two types of circuits are:
- Series circuit: all resistors are wired in a row, if one resister is removed the circuit is broken. ex= Christmas lights
- Parallel circuit: resistors are wired with an alternate path, removing one resistor does not effect the others (circuit is not broken). ex= wall outlets, car head lights.
400
One kHz is equal to 10^3 Hz. What is the wavelength (λ) of the electromagnetic waves sent out by a radio station whose frequency is 660 kHz?
The speed of light [V(c)] is 3 x 10^8 m/s
1 kHz = 10^3 Hz
λ= ? = d f= 660 kHz V(c)= 3.0 x 10^8 m/s
660 kHz/1 x 10^3 Hz/1kHz = 660,000
V=λ x f
3.0 x 10^8 = λ x 660,000 -> 3.0 x 10^8/660,000=
4.5454 -> 4.55 x 10^ 2 m (λ)
500
How does a suction cup and a straw work?
When "sucking" a liquid up a straw you are expanding the volume in your lungs causing the pressure inside you to decrease and now the outside air pressure is higher which then causes the liquid to be pushed up the straw.
When you push a suction cup to a wall you are pushing out all of the air(air pressure) out of that space which in turn creates a vacuum like effect= pressure inside is now lower then the pressure outside which makes it "stick" to the wall.
500
What are the Earth's true magnetic poles, and are the in the true location?
The "north pole" is actually a south pole magnet other wise all of our compasses would not point north. No the north/south poles are not in the true north pole location.
500
An opera performance is being broadcast by radio. Who will hear a certain sound first, a member of the audience 30 m from the stage or a listener to a radio receiver 5000 km away?
speed of light = 3 x 10^8 m/s
speed of sound = 343 m/s
V= D/T -> T= V/D
30 m/343 m/s = 0.087 s
5000 km -> 5 x 10^6 m/ 3 x 10 ^8 m/s = 0.017 s
* radio wave are technically light wave, and the speed of light is faster then the speed of sound, causing the person listening to the radio receiver 500 km away to hear the performance before the person who is actually in the audience.
500
When is resistance useful and when is it a problem?
Resistance is useful for safety reasons= the plastic coding on power cords to prevent us from getting shocked.
Resistance is a problem when is slows/ reduces the amount of electrical current is moved from one place to another (usually lost as heat, also the reason why power lines are hot to the touch).
500
a) A 240 volt clothes dryer draws a current of 15 A. How much energy in kilowatt-hours does it use in 45 minutes of operation?
b) If you pay $0.06 per kilowatt hour, how much does it cost to run the dryer in the above question for 45 minutes?
a) P= I x V I= 15 V= 240
P= 240 x 15 = 3600 W
3600 W/1 x 1 kw/1000 W = 3.6 kW 3.6(.75)= 2.7 kw-hr
45 min/1 x 1 hr./ 60 min = .75 hr.
b) 2.7 kw-hr. x $0.06 = $.162 or $.16