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Test2 Autumn 2001. (Click Here for Test for Tues/Thurs Lecture.) |
1. (33 points) In an insulated vessel, 90.0 g of ice at exactly 0 0C is added to
800.0 g of water at 25.00 0C. All the ice melts and the system is pure water at the final equilibrium temperature Tf >0. (See the diagram below for this situation.)
(a) (28) What is the total change in entropy ?
(b) (3) Based upon your answer in part (b), is the process reversible or irreversible? (Assume a closed system.)
(c) (2) Does the total disorder of the system increase or decrease ? Circle the correct word.
For the purposes of this problem, use LF = 80.0 cal/g and
CW = 1.0 cal/g0C.
2.(33 points) Three charges of equal magnitude q reside at the corners of an equilateral triangle of side length a. Assume q > 0.
(a) ( 28) Find the magnitude of the net electric field vector at point P, midway between the negative charges. Write your answer in terms of the symbols k, q, and a.
(b) (5) What is the direction of that net electric field vector at point P, midway between the negative charges? Draw an arrow to indicate that direction.
4B SP12 REFERENCE: FORCE AND FIELD FROM A DISCREET
SET OF POINT CHARGERS:
QUIZ 1 #47, #76
3. EXTRA CREDIT (Ch. 24) (7 points) 4B
SP12 REFERENCE: FORCE AND FIELD FROM A
LINE OF CHARGE:
QUIZ 2 #4, #38.
(a) ( 3)What is the magnitude E of the electric field at the point P a distance R from the infinitely long line of charge of charge density 
? Derive your expression and show all steps! Use symbols. Check out the figure below.
(b)(2 points) Suppose a point charge Q is placed at the location P described above.
If Q < 0, then what is the direction of the force of this charge ? Assume the point P lies in the plane of the page. Draw an arrow to show that direction.
(c ) (2) What is the magnitude of the force on the charge Q in part (b)? Use symbols.