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VU of Pakistan
Assignment 3: (Spring 2013)
TOTAL MARKS: 30
Due Date: 01/07/2013
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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
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, 5Ω and 15 Ω resistances as shown. In this circuit:
a. Electrons flow clockwise through the circuit.
b. The flow of current is greatest, through the 5 Ω resistor.
c. The light bulbs have different voltages over them.
d. The flow of current is least, through the 5 Ω resistor.
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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for question no.3 part1 use this equation to do calculation E=F/q
where E vector is electrical field(N/M) F vector is electric force in newtons and q is charge in coulombs
if any1 got an alternative idea or think this is not right feel free to rectify but be quick
Why can birds perch on high voltage lines without being injured?
Electrocution is injury or death that occurs because of electrical shock. If birds sitting on a wire are not getting electrocuted, this means they are not getting shocked by electricity. Essentially, this means that the electricity is able to pass through the birds without damaging them. Electricity works via electrons flowing through conductors. If a bird is able to sit on an electrical wire, it means that the bird is not a good conductor of electricity.
Birds are able to sit on electrical power lines because the electrical current essentially ignores the bird's presence and continues to travel through the wire. A bird's body is not a good conductor of electricity. Electricity, similar to water, flows using the least amount of resistance possible. In electrical power lines, electricity flows along copper wires. Copper is an excellent conductor of electricity in that it allows electricity to flow easily along its surface. A bird, on the other hand, is made of cells and tissues. These cells and tissues do not provide the electricity in the wire with an easier route to travel than the one it is already on. Because a bird's body is not a good conductor of electricity, the electricity essentially ignores the bird on the wire and continues to travel along the copper wiring to its destination.
While birds may sit on the wires of power lines and essentially be safe, they will not be so lucky if they happen to touch the ground while touching a power line. This is because the ground, or a transformer, or a place where the electricity is stored for use, is a place where there is essentially no voltage. Electricity travels from a place of high voltage to low voltage, just as water travels from high elevation to low elevation. A bird, or any living thing, that touches a wire (where electricity is moving from high voltage to low voltage) and also touches the ground (a place with no voltage) creates a path that allows the electricity to travel through that body and into the place with no voltage. When electricity travels through a body in this fashion, electrocution takes place, and the bird can die.
The power line is at a high voltage potential, but it is just that - a potential. The bird can perch on the line and come to the same potential voltage as the line with no shock. If there is no complete path from that potential to a higher or lower potential or to ground, no current will flow and the bird will not experience a shock. If you could jump up and grab that power line (without touching anything that would provide a path to ground) you could do the same thing that the bird is doing. Voltage does not hurt you absent current flow.
If the potential is high then a small segment of the line (the distance between the feet of the birds) will provide some potential difference. This will mean a current will flow through the bird. Is that correct? Although if we allow V small and R large than V=IR => small I. Is your argument that I in this case is too small to cause the bird harm. Someone dangling on the voltage lines will not cause harm for the same reason although provided their arms are not too widely spaced? Otherwise the potential difference will be larger however R for a human is smaller than a bird.
n@z gud keep it up & thanks for sharing
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M.Tariq Malik u r well ComE :) u also RockinG :)
N@z, You're very best
any ideas about question no 5???????