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Sunday, 30 November 2014

Intermediate English XI Synonyms Ch 5 The Piece of String

Intermediate English XI Synonyms Ch 5 The Piece of String

Page No 32:
Market: day, trade, business day.                           
Gigs: two wheeled one wheel carriage.            
Dump carts: heavy duty, trucks.                            
Appetizing: tempting,irritating.                         
Odour: aroma, fragrance.              
Appetite: hunger.                       
Affairs: exchange, exhibition.             
Favorable: conducive, suitable.               
Discuss: debate.                                               
Attentive: alert, concentrating.               
Announcement: declaration, proclamation.   
Inhabitants: resides, dwellers.                      
Caretaker: custodian, guardian.         
Appeared:  showed up.                                     
Stout: plump, fleshy.               
Suspicion: skepticism, mistrust, harnesses man.       
Credence: belief, trust, confidence.  
Mistook: misjudge, miscalculate.

Page No 33:
Furiously: wrathfully, indignantly.                            
At least: testify, affirm.                                            
Exasperating: annoying, irritating.                          
Salvation: redemption, rescue.                               
Chocked: suffocate, stifle.                                  
Indignation: rage, fury, anger.                                 
Maintained: insisted on.                                             
Warning: notice, threat.                                         
Statement: declaration.                                               
Presentation: display, exhibition.                             
Adventure: enterprise episode.                                    
Incredulity: disbelief, doubt.                                    
Neighborhood: locality, vicinity, surrounding.                
Triumph: victory, success.                                       
Grief: pain, distress.                                                     
Grieved: hurt, saddened, crushed, distress.              
Shameful: disgraceful, mean, dishonorable.            
Excuses: justifications, pretence.                             
Disgrace: humiliation, dishonor.                                
Esteem: egoism, respecter, self-esteem.                   
Consumed: eaten up, used.                                           
Wasted: away, weakened.                                       
Campaign: expedition, war.                                      
Touched: affected influence.                                    
Delirium: frenzy, hysteric.                                             
Claiming: maintaining, asses, declaring.                   
Reiterating: repeating, restating.

Page No 34:
Wrath: anger, fury, rage.                                         
Belongings: possessions, assets.                         
Withstood: endured, bore.                                      
Havoc: destruction, devastation, damage.                  
Engraved: carved, inscribed, imprinted.                  
Tombstone: monument.

Written By: Asad Hussain

Saturday, 22 November 2014

F.Sc Notes: Physics XII: Chapter 13 Current Electricity Exercise Short Questions:

FSc Notes: Physics XII: Chapter 13 Current Electricity Exercise Short Questions:                                       

Question 13.1 A potential difference is applied across the ends of a copper wire. What is the effect on the drift velocity of free electrons by
  1. Increasing the potential difference.
  2. Decreasing the length and the temperature of the wire.
Answer 13.1 Drift velocity is actually the resultant velocity of electrons in the presence of an external electric field.
  1. By increasing the potential difference, value of drift velocity of free electrons increases.
  2. When length and temperature of the wire is decreased resistance also decreases, with the decrease in resistance drift velocity of free electrons increases.

Question 13.2 Do bends in a wire affect its electrical resistance? Explain.
Answer 13.2
No, as we know that R = ρ L/A it shows that there is no relationship b/w resistance and the bends of a wire i.e. R is independent of the bends in a wire. Hence Bends in a wire don’t affect its resistance.

Question 13.3 What are the resistances of the resistors given in the fig A and B? What is the tolerance of each? Explain what is meant by the tolerance?
Answer 13.3
Fig A: Brown 1 Green 5 Red 00 Gold 5% tolerance 1500Ω with 5% tolerance.
Fig B: yellow 4 White 9 Orange 000 Silver 10% tolerances 49000Ω with 10% tolerance.

Question 13.4 Why does the resistance of a conductor rise with temperature?
Answer 13.4
Actually resistance of a conductor is due to collision b/w electrons and lattice atoms with increase in temperature, vibration motion of atoms increases and due to greater amplitude of vibration, their collision probability with electrons increases hence resistance of conductor increases according to the relation: 
Rt = R0(1+at)
Rt Resistance at t temp, R0 Resistance at 0 temp, a Co-efficient of resistance, t change in temp.

Question 13.5 What are the difficulties in testing whether the filament of a lighted bulb obeys Ohm’s Law?
Answer 13.5
Ohm Law states “Current is directly proportional to the potential difference applied across the conductor provided that the physical state of the conductor remains constant (V=IR).” The resistance of a lighted electric bulb does not remains constant but gradually increases with increase in temp. Hence the filament of a bulb does not follow Ohm’s Law.

Question 13.6 Is the filament resistance lower or higher in a 500W, 220V light bulb than in a 100W, 220V bulb?
Answer 13.6
As we know that:             Power P=V2/R or R= V2/P
Case i: when V=220V & P=500W so R1= (220)2/500 =96.8Ω
Case ii:
when V=220V & P=100W so R2= (220)2/100 =484Ω
Conclusion From R2 R1. It is clear that filament resistance in 500W and 220V bulb is lower than in 100W, 220V bulb.

Question 13.7 Describe a circuit which will give a continuously varying potential.
Answer 13.7
Potentiometer is a circuit that can give a continuously varying potential as shown in figure: A and B are fixed terminals and C is sliding terminal Resistance b/w A and B is ‘R’ and that b/w A and C is ‘r’.
Now I=V/R and potential drop across ‘r’ is V=I\r
As C moves from A to B r varies from 0 to R. Hence a circuit is described which gives a continuously varying potential 0 to V.

Question 13.8 Explain why the terminal potential difference of a battery decreases when the current drawn from it is increased?
Answer 13.8
As we know that vt = E-Ir ----------I
Here vt = terminal velocity, potential difference E=emf, r=internal resistance of battery.
According to eq when current (I) drawn from the circuit it is increased by factor ‘Ir’.
That is why, the value of vt decrease, when current is increased.

Question 13.9 What is Wheatstone bridge? How can it be used to deter mine an unknown resistance?
Answer 13.9
That device is used to find the unknown resistance is known as Wheatstone bridge.
An unknown resistance can be found by the relation: R1 / R2 = R3 / R4.

Written By: Asad Hussain

Wednesday, 19 November 2014

F.Sc ICS Notes: Physics XII: Chapter 12 Electrostatics Exercise Short Questions:

FSc Notes: Physics XII: Chapter 12 Electrostatics Exercise Short Questions:

Question 12.1 The potential is constant throughout a given region of space. Is the electrical field zero or non-zero in this region? Explain
Answer 12.1
Electric field is defined as “the negative of the potential gradient
i.e. E= - ΔV / Δr.
If electric potential is constant over a given region of space then potential difference between any two points is zero.
ΔV = 0 As ΔV / Δr=0 .
So E=0 Hence the electric field is zero in that region of sphere.

Question 12.2 Suppose that you follow an electric field line due to positive point charge. Do electric field and the potential increase or decrease?
Answer 12.2
The electric due to positive charge is always directed outward from the charge, so if we are following a field due to such a charge our distance r from the charge is increasing.
Since V=kq/r and E=kq/r2 .
This implies E∝1/r2 and V∝1/r.
Hence Both E and V will decrease in such a case.

Question 12.3 How can you identify that which plate of a capacitor is positively charged?
Answer 12.3
The presence of charge is detected by a device called “Gold leaf Electroscope” on bringing charged plate or disc close to the plate of gold leaf electroscope.
  1. If divergence of plates increases then the plate is positively charged.
  2. If divergence of plates decreases then the plate is negatively charged.

Question 12.4 Describe the force or forces on a positive point charge when placed between parallel plates.
a. With similar and equal changes.
b. With opposite and equal charge.
Answer 12.4 (a)
When a positive charge is placed between two parallel plates having similar and equal charges, the net force acting on the charge will be zero.
(b) When the charge is placed between the plates having equal but opposite charge, the positive charge will move from positive plate to negative pate.

Question 12.5 Electric lines of force never cross. Why?
Answer 12.5
Actually, the direction of electric field lines at a certain point represents the direction of motion of a unit positive charge when placed at that point. Now if two lines cross each other then, at that point of intersection, a positive charge will have two directions of motion when placed there. It is not possible at all. So, electric lines of force never cross each other.

Question 12.6 If a point charge q of mass m is released in a non-uniform electric field with field lines pointing in the same direction, will it make a rectilinear motion?
Answer 12.6
Non uniform field means that lines of force are neither parallel nor equally spaced.
  1. Case 1: When electric field is due to a single isolated charge, the charge ‘q’ of mass ‘m’ will make rectilinear motion.
  2. Case 2: When the field is due to two oppositely charged particles then q will not make rectilinear motion.

Question 12.7 Is E necessarily zero inside a charged rubber balloon if balloon is spherical? Assume that charge is distributed uniformly over the surface.
Answer 12.7
Yes, E is necessarily zero inside a rubber balloon if balloon is spherical and charge is distributed uniformly over the surface. According to Gauss’s Law. Flux density = φe = 1 / ∈(Charge enclosed)
φe = 1 / ∈(0)-------------I
φe = 0
As  φe = E • A------------II
From (i) and (ii)
here   A is not zero         E=0              
Hence, electric intensity E is zero inside a spherical balloon.

Question 12.8 Is it true that Gauss’s law states that the total number of lines of force crossing any closed surface in the outward direction is proportional to the net positive charge enclosed within surface?
Answer 12.8
Yes, it is true that total number of lines of force crossing any closed surface in the outward direction is proportional to the net positive charge enclosed within the surface
i.e. Flux density = φe = 1 / ∈(Charge enclosed) or Flux = Constant (Total Charge Enclosed)                                                              
that is Flux ∝ Total charge enclosed.

Question 12.9 Do electrons tend to go to region of high potential or of low potential?
Answer 12.9
As e- carries negative charge, it will move from a point at lower electric potential to a point at higher potential in an electric field.

Written By: Asad Hussain