physics questions

Write up a solution to each Problem. The solution must follow the format of the six-step Structured Problem Solving Method. This method provides structure, and will help you clearly reflect your understanding of the problem and your solution. Please see format below:

Structured Problem Solving:

A major difficulty that students will often encounter is an inability to approach a problem in a systematic manner. The following procedural method is intended to guide you through solving any physics problem. My further hope is that through using this process you will realize that any problem in life, no matter how difficult is appears to be, can be addressed by breaking it down into steps.

Key Idea: Write down a short statement of the physical principle which you think is the most relevant to solving the problem. Describe the elements of the problem which indicated that this physical principle might be applicable.

Stock of Data: Make a list of the numerical data you are given in the problem description. Be sure to include units. List quantities you are asked to calculate with trailing question marks. This step may include a diagram indicating your understanding of the problem.

I.D. Equation: Choose an equation which reflects both the key idea of your problem and information from your stock of data. You may need more than one equation.

Solve: If the equation or equations you have chosen are not already solved for you unknown then do the algebra to accomplish this now. Be sure to show enough detail in each step so that a reader can follow your work.

Substitute in Numerical Data: Once you have an analytic solution, substitute numerical values into the analytic solution to obtain the final answer.

Sanity Check: Answer the question. “Does this answer make sense in light of the rest of the knowledge I possess?” The sanity check could include a back of the envelope calculation done with a single significant digit or a unit analysis of the final answer.

Please see homework below, each problem must follow the format above:

1.  Suppose all the electrons could be removed from earth.

(a) Find the force on a proton just above the Earth's surface under these conditions.

(b) Compare your answer in part (a) with the weight of the proton.

2.  Four point charges are placed on the corners of a square of side d as shown in picture.

(a)   Find the net force (magnitude and direction) of each charge.

3.  Three capacitors are in series: C1= 45 µF, C2=65 µF and C3=80 µF. (a) Compute the equivalence capacitance. The series combination is connected across a 48-V battery. (b) Find the charge of each capacitor. (c) Compute the energy stored in each capacitor. (d) Show that the total energy you found in part (c) is the same as would be stored in a single capacitor with the equivalent capacitance you found in part (a).

4.  Defibrillator: energy and power. A defibrillator uses a 225-µF capacitor charged to 2400 V. (a) how much energy is stored in the capacitor. (b) What is the power delivered to the patient if the capacitor discharged completely in 2.5ms?

5.  Ion channel. The potential differences across the ion channel described in example 17.1 is 80 mV. (a) What is the resistance of the Ion channel? (b). The Ion channel can be modeled as a cylinder with a length of 6.0 nm and a diameter of 0.35 nm. What is the resistivity of the fluid filling the channel? (c) At what rate is energy dissipated while the ions are flowing?

6.  Two long parallel wires each carry 2.5 A in the same direction, with their center 1.5 cm apart.

(a)  Find the magnetic field halfway between the wires.

(b)  Find the magnetic field at a point in the same plane as the wires, 1.5 cm from one and 3.0 cm from the other.

(c)  Find the force of interaction between the wires, and tell whether it is attractive or repulsive.

7.  Four long parallel wires pass through the corners of a square 2.0 cm on a side. The wires each carry 2.5 A in the same direction.

(a)  What is the magnetic field at the center of the square?

(b)  What is the force per unit length on each wire?

Problem 8 and 9 are in the picture below: