Physics 2
How does heat relate to temperature? How would you calculate the heat resulting from a system that changes temperature? Therefore what about Energy and Temperature?
-Heat is the movement of energy -Temperature is the average kinetic energy of all molecules in a system ...something doesn't have "heat", but it does have temperature. And when experiencing heat (transfer of energy from something of high temp ie avg energy to low temp) that means something gained temp and the other lost temp. Similarly, if something increased its temperature that means that there was heat transfer. So we calculate with the equation: Since energy = Q +/- work, then energy is not equal to but proportional to temperature (ie if temp doubles then energy doubles)
Work can be calculated as the area under what two curves?
1) P x V - (heat engine graphs) -makes sense bec P=F/A. So F/A * V = Fd 2) Force x position
If a magnetic field is pointed into the page, and an electron and proton enter the field moving to the right, which way will: 1) the electron move? 2) the proton move?
1) electron: down 2) proton: up (for electrons you flip the force) *Remember that with an ELECTRIC field, the force direction would just be toward the - side for a proton
A system of two charges has a potential energy of -5 joules. Which of the following is a possible potential energy for the system after it has been permitted to accelerate for a few seconds? 1) 0 J 2)-10 J
2) -10 J Recall we are dealing with opposite charged particles when U is negative. So when the two are allowed to accelerate towards each other you know that they will attempt to reduce the PE and turn it to KE (we're on the bottom half of the U graph) so PE must decrease
An object made of silicon (specific heat = 698 J/kg°C) absorbs 3500 J of heat while increasing its temperature from 43°C to 53°C. What is the approximate mass of the object?
= 0.5 kg Using the equation, the heat (in joules) added corresponds to a specific heat of a substance, the mass, and the change in temperature experienced
Going from a lower index of refraction medium to a higher one, the ray will A) bend closer to normal line (bigger angle of refraction) B) bend closer to normal line (smaller angle of refraction) C) bend away from normal line (bigger angle of refraction) D) bend away from normal line (smaller angle of refraction)
B. moving to a more refractive medium means refraction angle will be smaller than incidence angle
Will a red or blue light wave get bent more on a prism?
Blue Entering a higher n medium simply means that velocity of the wave decreased Red has the looongest wavelength (think oozing blood) and thus will pass through "smoothly" Blue is of higher frequency. Higher frequency waves experience more refraction
Conduction vs. Convection vs. Radiation
Conduction: heat transfer via contact Convection: heat transfer via liquid (gas is a liquid too!) - convection setting on an oven is when a fan blows the heat to the food (so the heat is via gas transfer) Radiation: heat transfer via electromagnetic radiation
1) Consider a wire loop in the plane of the page with current traveling clockwise. Is the field inside the loop pointing at you or away from you? 2) Consider two wires next to each other with both of their currents pointing upward on the plane of the page. Will the wires be brought together or pushed apart?
For a current's magnetic field -> Current is thumb, fingers wrap to form field 1) Away from you 2) Brought together Think of the field produced by each (using finger to wrap around). Then use right hand rule (pointer finger is either motion of a charged particle for some problems, or in this case - direction of current). So for the wire on the right for example, fingers into page (field produced by left wire), pointer finger up (current), force has to be left (thumb).
Explain how frequency of a sound wave varies with the mediums: 1) stiffness 2) thickness In the context of the cochlear membrane
Frequency is higher with MORE stiffness and LESS thickness. On the cochlear membrane it goes from base (stiff & thin) to apex (thick and loose). Coincidentally, you highest frequencies are at the base and the lowest are at the apex
The first law of thermodynamics states that there are two ways to change the internal energy of a system:
Heat and work. These are not intrinsic properties of a system, their meaning is simply defined by a *transfer* of energy. Heat and work are the only ways energy can be transferred from one thing to another. Change in E of a system= Q + W If work is done on the system (gas) it is positive (and vice versa) ^same goes for the heat
How is intensity of any wave relates to power and area?
I = P/A ie energy per time over a certain area
What does Bernoulli's equation say about the relationship between pressure and speed at a given point? Why are the components in terms of density?
Inverse relationship- More pressure = slower speed The pressure referred to in Bernoulli'a equation is that of internal pressure (ie the pressure that the water produces amongst itself and outward onto the walls) -> distinct from the usual pressure of walls onto the fluid. So think, if it's moving fast af through a stretch of tube then it doesn't have time to push outward) The density used instead of mass makes it so that each term (PE, KE) etc is PER UNIT VOLUME
What does an isotherm mean and what does it look like on a graph? What about Adiabatic?
Isotherm = temp (avg kinetic energy of particles) doesn't change = energy doesn't change. How does this to happen with, for ex positive work(volume decreasing)?: + work would increase the energy, but the system isn't contained so that increase in energy from the work will just dissipate out via heat (negative Q). Graph: Constant temperature means constant PV (PV=nRT). Thus, the graph must be a line where decreasing P must have an increase in V etc Adiabatic= insulated -> Q can't change. All the work put in becomes energy (E = W). Graph is steeper
When a wave travels into a medium with a higher refractive index does it speed up or slow down? Bend towards or away from normal? Give an equation to relate 1) refractive indexes to speeds of two mediums and 2) refractive indexes to angles
More refraction (toward normal), slows down
Would someone will nearsightedness need a converging or diverging lens?
Nearsightned- can't see far (patricia) eye lens converge the image in front of retina, need to spread them out -> need diverging lens
What is the Power equation (non electrical power). How is Intensity related to power? If a 0.01 W sound gets amplified by 30dB over the course of a basilar membrane, what is the final power?
P = Work / time Intensity is just power per unit of Area. And in the Intensity dB equation, the denominator threshold intensity is just 10^-12. This equation, confusingly enough, can be spoken in terms of power, intensity, etc, you just change the units. But most problems you don't even need to know that detail
Suppose you have a charged particle between a capacitor who's top plate is the positive one. If an particle (q) moves to the right between the capacitor plates, and the magnetic field points into the page, was the particle a proton or electron?
Particle would be an electron. Velocity (direction) is pointer finger. Fingers= field. Since the force is the thumb, it must be directed upwards, meaning this charge is an electron (attracted to positive plate)
Oxidation occurs at the (cathode.anode)? Electrons flow to the (cathode/anode)?
Red cat...An Ox (reduction-cathode, anode-oxidation) Electrons flow to the cathode (because things getting reduced gain electrons, charge reduced)
The area enclosed by the four steps shown in Figure 2 represents (flip): ...Why? A. the work done on the engine during one complete cycle. B. the work done by the engine during one complete cycle. C. the thermal energy change of the surroundings during one complete cycle. D. the heat transferred out of the engine during one complete cycle.
Represents the work done by the engine. This makes sense because if there is an area under the curve (top line is moving right which is negative work direction) that means that there will be a net negative work. This corresponds to work done BY the system on surroundings
If someone tries to echolocate (sound waves) an object underwater and falsely assumes the speed of sound is the same as that in air, will he over or underestimate the distance of the object?
Speed of sound waves in water is faster because closely packed molecules can transmit the vibrations more effectively. So he is underestimating the velocity of the wave. Thus, let's say a wave comes back to you in 1s. If you had thought it was traveling at 100 m/s instead of 200 in reality, then you would assume the person is 100 m away instead of 200. Underestimated distance
What does temperature say about the kinetic energy of particles?
Temperature is the average speed (KE) of particles. So two gases at the same temperature will have molecules of the same average KE
How can the efficiency of a heat engine be calculated?
The efficiency is how much work is done by the engine per energy given to it. The W is essentially the difference between the Q put in and the Q lost out. (W + Q lost must be = Q in for energy to be conserved) So efficiency (W/Qin) is also equal to Qin-Qout / Qin
Which way does each point, + > - ... or - > + ? a) current in a circuit b) electric field
They both point from positive to negative (however inside the battery current points - to pos)
For an isometric process, what is the sign of work and why?
Work is 0. (area under curve is zero). This is also explained by the fact that the volume doesn't change (the piston doesn't move) so without distance there can't be work
For an isobaric condition in which you are increasing volume, what sign is given to work?
Work is negative. For these graphs think of the gas as the system. If the volume of the gas increases, that means it is pushing the sides of the container (ie performing work onto the surroundings) -> negative work done
Which of the following depend on both the point charge and the source charge? -V -U -E -F
U and F
If you blow air over a glass of water, the water gets pulled out. Why? -Venturi effect -diffusion -dispersion
Venturi Effect: -bernoulli's principle explains how a faster flowing region will result in a drop in pressure... and venturi effect is when that drop in pressure causes the fluid/air adjacent to be pulled toward it (things move from high to low pressures) -Diffusion is the movement from high -> low pressure. -Dispersion describes how waves get refracted (bent), and the refraction index is dependent on the frequency of the wave
An object of density 800 kg/m^3 is floating on the surface of water that has a density of 1000. What fraction of the ball is above the surface of the water?
When floating at rest, the buoyant force must be equal to the weight force of the object
In myopia, the focal length of the lens is too (short/long). This is called (nearsightedness/farsightedness)
focal length of convex (aka converging) lens such as in the eye= the distance between the lens and where the light ray focal points will converge Too short. The image falls short of the retina, ie too much lens refractive power, ie cannot see far images, ie NEARSIGHTED Patricia is myopia- she can't see far stuff
For a electric potential energy graph, do "like" charges occupy the positive or bottom portion of the graph?
like charges on positive half (remember U = kQq/r so the signs of like charges will always multiple to be positive -> top of graph. As you decrease distance with two like charges the energy must increase and vice versa for opposite charged particles
When referring to a charge moving through a uniform magnetic field, what is the equation for the Force it would experience? What if the charge wasn't moving?
the portion of velocity that is perpendicular to the field charges only experience a force if they are moving at an angle with the magnetic field (not 0 or 180 degrees, max at 90)
Current can be defined as ___. It refers to the directional movement of (positive/negative) charges.
the rate of positive charge per time (positive)
