Assignment 3: (Spring 2013)

Physics (PHY101) VU of Pakistan 
Assignment 3: (Spring 2013) 
PHYSICS (PHY101) 
TOTAL MARKS: 30 
Due Date: 01/07/2013 
DON’T MISS THESE Important instructions: 
• To solve this assignment, you should have good command over first 28 lectures. 
• Upload assignments (Microsoft word) properly through LMS, (No Assignment will be 
accepted through email). 
• Write your ID on the top of your solution file. 
• All students are directed to use the font and style of text as is used in this document. 
• Don’t use colorful back grounds in your solution files. 
• Write to the point and avoid from unnecessary explanation. Don’t copy/paste from 
internet or any other source. 
• Use Math Type or Equation Editor etc for mathematical symbols. 
• This is not a group assignment, it is an individual assignment so be careful and avoid 
copying others’ work. If some assignment is found to be copy of some other, both will be 
awarded zero marks. It also suggests you to keep your assignment safe from others. No 
excuse will be accepted by anyone if found to be copying or letting others copy. 
Don’t wait for the last date to submit your assignment. 
Question # 1 
Two charged spheres are held a distance, r, apart. One sphere has a charge of +4µC, and the other sphere has a 
charge of +8µC. Compare the force of the +4µC sphere on the +8µC sphere with the force of the +8µC sphere 
on the +4µC sphere. (Note: Answer should not be greater than a one line). Marks = 5
Question # 2 
I. When do you wipe a compact disc with a clean cloth, why does the CD begin to attract 
dust again? 
II. The constant, K, in Coulomb’s equation is much larger than the constant, G, in the 
universal gravitation equation. Of what significance is this? Marks = 5 (2+3) 
Question # 3 
I. A positive charge of 5.0×10
-7
C is located in a field of 30 N/C directed toward the south. 
What is the force acting on the charge? 
II. How is the direction of an electric field defined?
III. Why can birds perch on high voltage lines without being injured? Marks = 9 (5+2+2) 
Physics (PHY101) VU of Pakistan 
Question # 4 
Jamil and Salma are standing on an insulating platform and holding hands when they are given a 
charge, as in Figure Jamil is larger than Salma. Who has the larger amount of charge, or do they 
both have the same amount? Marks = 4
Question # 5 
The circuit above shows two 1.5V batteries connected so that the current flows through the three 
light bulbs which have 10 Ω, 5Ωand 15 Ωresistances as shown. In this circuit: 
a. Electrons flow clockwise through the circuit. 
b. The flow of current is greatest, through the 5 Ωresistor. 
c. The light bulbs have different voltages over them. 
d. The flow of current is least, through the 5 Ωresistor. 
e. The batteries and light bulbs are connected in parallels. 
Note: Explain the reason of your above selected choice as well. 
Marks = 7(3+4) 

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