In: Physics
Cell Membranes and Dielectrics
Many cells in the body have a cell membrane whose inner and outer surfaces carry opposite charges, just like the plates of a parallel-plate capacitor. Suppose a typical cell membrane has a thickness of 6.1×10^−9 m, and its inner and outer surfaces carry charge densities of −7.7×10−4 C/m^2 and +7.7×10^−4 C/m^2, respectively. In addition, assume that the material in the cell membrane has a dielectric constant of 3.1
(a) Find the direction of the electric field within the cell membrane. a) into the cell b) out of the cell
(b) Find the magnitude of the electric field within the cell membrane.
(c) Calculate the potential difference between the inner and outer walls of he membrane (Note: express answer in millivolts,)
(d) Which wall has the higher potential a) inner wall b) outer wall
Into the cell
Out of the cell
(b) Find the magnitude of the electric field within the cell membrane.
E=E= Answer NCNC
(c) Calculate the potential difference between the inner and outer walls of the membrane. (NOTE: Express your answer in millivolts, mV.)
ΔV=ΔV= Answer mVmV
(d) Indicate which wall of the membrane has the higher potential.
Inner wall
Outer wall
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1) An unmarked police car, traveling a constant 95 km h , is passed by a speeder traveling 145 km h . Precisely 1.00 s after the speeder passes, the policeman steps on the accelerator. If the police car’s acceleration is 2.00 fracms2 , how much time elapses after the police car is passed until it overtakes the speeder (assumed moving at constant speed)?
2) Assume in Problem 1 that the speeder’s speed is not known. If the police car accelerates uniformly as given above, and overtakes the speeder after 7.00 s, what was the speeder’s speed?
3) A mass of 3.2 kg is dropped from a height of 4.63 m above a vertical spring anchored at its lower end to the floor. If the spring constant is 32 N cm , how far to the is the spring compressed?
(a)31.1 cm, (b) 34.5 cm, (c)36.8 cm , (d)45.9 cm.
4) A planet/moon has a mass of 82.91 × 1023 kg and a radius of 10.32 × 106 m. What is g on the surface of this planet?
(a) 0.005 m s 2 , (b) 1.04 m s 2 , (c)4.67 m s 2 , (d) 5.19 m s 2 .
In: Physics
How to
design an experiment
In a lab, you will have access to a mystery metal, a string, a retort stand, a beaker, a kettle, water, two thermometers, a stopwatch, a weight scale, and an insulated container with cup and lid. The metal can be submerged in the container of water such that the water provides a temperature bath for the metal. Design determine the specific heat capacity of the mystery metal. In your preparatory assignment: brass an experiment that use the equipment provided to
1. Describe your experimental design witha labelled diagram.
2. State the assumptions you are making in your design, if there are any.
3. Suggest the likely sources of experimental uncertainty and your strategies to minimise them.
( Don't forget to include the brass cup as part of your analysis! Look up a value for the specific heat capacity of brass and cite the source)
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Can you explain the use of X-rays for determining the structure of solids and for medical imaging (CT scans) and explain the main physical difference between the two? I'm confused as to how they're different.
In: Physics
A solid motor has an average thrust of 67,000 N, a specific impulse of 285 sec, and a propellant mass fraction of 0.92. Calculate the total mass of the vehicle for a 42 sec burn time.
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Bob has just finished climbing a sheer cliff above a beach, and wants to figure out how high he climbed. All he has to use, however, is a baseball, a stopwatch, and a friend on the beach below with a long measuring tape. Bob is a pitcher and he knows that the fastest he can throw the ball is about ?0=31.7 m/s. Bob starts the stopwatch as he throws the ball (with no way to measure the ball's initial trajectory), and watches carefully. The ball rises and then falls, and after ?1=0.910 s the ball is once again level with Bob. Bob cannot see well enough to time when the ball hits the ground. Bob's friend then measures that the ball landed ?=128 m from the base of the cliff. How high up is Bob, if the ball started exactly 2 m above the edge of the cliff?
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You're driving down the highway late one night at 15 m/s when a deer steps onto the road 42 m in front of you. Your reaction time before stepping on the brakes is 0.50 s , and the maximum deceleration of your car is 11 m/s^2 .
1.
How much distance is between you and the deer when you come to a stop?
Express your answer using two significant figures.
2.
What is the maximum speed you could have and still not hit the deer?
Express your answer using two significant figures.
In: Physics
In the World Series the first team to win four games wins the championship. If the two teams are evenly matched, then the probabilities that the series will be decided after 4, 5, 6, or 7 games are given below. a) What is the expected number of games that will be required to decide the championship? b) Calculate the probabilities. Explain your logic and show all work.
Number of games: 4, 5, 6, 7
Probability: 1/8, 1/4, 5/16, 5/16
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Explore the Electrical Safety Foundation International's web pages on home safety located within the weekly readings. Then answer the following questions:
What are the dangers associated with electricity in your home?
What can be done to limit or prevent the possibilities of dying or getting hurt?
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An insulated cylinder is initially divided into halves by a frictionless, thermally conducting piston. On one side of the piston is 1 m3 of a gas at 300 K, 2 bar. On the other side is 1 m3 of the same gas at 300 K, 1 bar.The piston is released and equilibrium is attained, with the piston experiencing no change of state. Employing the ideal gas model for the gas, determine
(a) the final temperature, in K.
(b) the final pressure, in bar.
(c) the amount of entropy produced, in kJ/K.
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A 200 g mass hangs from a massless spring (k = 10 N/m). At t = 0.0 s, the mass is 20 cm below the equilibrium point and moving upward with a speed of 100 cm/s. What is the a. oscillation frequency? b. distance from equilibrium when the speed is 50 cm/s? c. distance from equilibrium at t = 1.0 s?
In: Physics
calculate the mass collision stopping power for a 20-MeV proton in lead, without the shell correction.
Answer: 11.6 MeV cm^2/g
In: Physics
We have potential of
V (x) = ( 0, 0 ≤ x ≤ a.
∞, elsewhere.
a) Find the ground state energy and the first and second excited states, if an electron is enclosed in this potential of size a = 0.100 nm.
b) Find the ground state energy and the first and second excited states, if a 1 g metal sphere is enclosed in this potential of size a = 10.0 cm.
c) Are the quantum effects important for both systems? Explain why or why not.
d) Use the uncertainty principle to estimate the velocities of the electron and the metal sphere.
In: Physics
Make an argument for what mix of energy you see the world powered by in 2050. Include in your analysis – in words – not equations: What mix of stationary power will there be, and why? What will power our transportation system (focus on vehicles, you may neglect airplanes and ships)? What fraction of energy will be used for transportation and what fraction will be for stationary power? What role will power providers play, and what role will consumers play in driving this 2050 energy mix?
In: Physics