PHY101 - Physics Assignment No. 03 Solution and Discussion Fall 2014 Due Date: 10/7/2014

[+ M.Tariq Malik]

Assignment 3: (Spring 2014) 
Page
1 
PHYSICS (PHY101) 
TOTAL MARKS: 30 
Due Date: 10/07/2014 
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•  

[+ M.Tariq Malik]

Q no 1:

R=V/I 

using Ohms law 

R=260/120

R=2.16Ans

otherwise : the solution is like this 

watts to amps conversion:

watts/volts= amps

=120/260=0.46 amps

now use this =

R=V/I

R=260/0.46

R=565.21Ans

check it according to handouts !!

[+ M.Tariq Malik]

Qno2:

If the resistor is in series with the circuit, it will impede the flow of current, decreasing the current into the circuit. If the resistor is in parallel with the circuit, that added resistor will provide another path for current thus increasing the current out of the voltage supply but not effecting the current into the circuit since the supply voltage is independent of current which means the circuit would see the same voltage across it.

In general, when the voltage is constant the current will decrease as the resistor value increases.

Answer of Q no 2:

When current passes through a resistor, it  stay same 

because the resistance at any position has a constant value , but if u affect it by heat or you changed the material of it or change its long or cross sectional area , then it will change according to this relation R=p *(L/A)

where R is the resistance 
p is the specific resistance (depends on the material of the resistor) 
L is the resistors long 
A is the cross sectional area of the resistor

Current "splits" at principle nodes 
remains same at resistors 

Voltage drops at resistors

[+ M.Tariq Malik]

Qno 3:

No. 

A current requires an overall flow of charge (either positive or negative) from one position to another. E.g current flows down a wire when electrons enter one end of the wire and leave from the other end. The protons (positive charges) in the wire stay fixed. 

A person is neutral (equal numbers of positive charges (protons) and negative charges (electrons)), so there is no overall movement of charge when a person walks by because the positive and negative charges move together.

[+ M.Tariq Malik]

Q no 4 hint :

Suppose that a negatively charged rubber balloon is brought near a single sphere as shown below (Diagram ii). The presence of the negative charge will induce electron movement in the sphere. Since like charges repel, negative electrons within the metal sphere will be repelled by the negatively charged balloon. There will be a mass migration of electrons from the left side of the sphere to the right side of the sphere causing charge within the sphere to become polarized (Diagram ii). Once charge within the sphere has become polarized, the sphere is touched. The touching of the sphere allows electrons to exit the sphere and move through the hand to "the ground" (Diagram iii). It is at this point that the sphere acquires a charge. With electrons having left the sphere, the sphere acquires a positive charge (Diagram iv). Once the balloon is moved away from the sphere, the excess positive charge redistributes itself (by the movement of remaining electrons) such that the positive charge is uniformly distributed about the sphere's surface.

[+ M.Tariq Malik]

Q no 5 hint :

How much energy is released when the capacitor is discharged?
Energy stored= 1/2 C*V^2 = 1/2 (20E-6)(4000^2 = 160 J

c. If the capacitor completely discharges in 2.0 ms, what is the average current
delivered by the defibrillator?
I = Q/t = .08/.002 = 40 A

[+ M.Tariq Malik]

for Q no 5 u will use formula 

I=Q/t

where Q = C*V

Hope its helpful now !! 

[Ahmad]

give a complete solution.

[bint e arshad]

r u get full solution?????????

[Abu Bakar (BSCS 7th)]

Ans:

e) The balloon will cause a polarization of charge in the sphere

There is negative charge on balloon due to extra electron deposited on it whenever a neutral body i.e. a metal sphere in this case is brought near to it then it will begin to polarization(division) of charge because it is the nature of an object to tends to be neutral.

[+Abbas Niazi]

full solution do yar 

[bint e arshad]

koi to solution upload kro plzzzzzzzzz

[Bl@ck Ro$e]

Question no 2

ans:

This is wrong statement because when current passes through the resistors it gets hot and its resistance increases

See page 74 lec 26 for example