### Answers to Review Questions: Ch # 14 Magnetism and Electromagnetism

Karachi Board ( BSEK)

Note: For complete questions use the book.

Q.14.1 What is flux density and how is it related with the number of lines of induction expressed in Weber?
Ans. Magnetic flux density B is the magnetic flux per unit area (B=φ/A).and its unit of flux density is Weber per meter square or Tesla (T).The number of magnetic line of forces passes through surface is also known as magnetic flux density. Each line is known as Weber.

Q.14.2 Charged particles fired in vacuum tube hit a fluorescent screen. Will it be possible to know whether they are positive or negative?
Ans. Yes it is possible .it can be found by applying magnetic field perpendicular to the motion of particle and then the deflection can be observed. The positive charge in an inward filed will deflect upward.

Q.14.3 Beams of electron……………………is doubled?
Ans. The radius of circular path of particle in a magnetic field is r=mv/qb. Which shows that  is directly related to the mass but deflection is inversely related to the mass>so the electron is lighter and will be deflected more. and if the velocity is doubled the radius will be doubled.

Q.14.4 A circular loop of wire hangs………. Earth’s magnetic field?
Ans. The front face of the coil turns in the direction of geographic North Pole.(Left hand Rule)

Q.14.5 Imagine that the room in…………………..magnetic origin?
Ans. The direction of current in the loop, as viewed from the above will be clock wise.(left hand rule)

Q.14.6 Two identical loops…….machine generates?
Ans. The copper and aluminum has different conductivities, they show different behavior in the induction. Copper having the higher conductivity will have the large e m f.
The electric generator does not generate electricity it is already present in the conducting coil.
They convert mechanical energy in to electrical energy.

Q.14.8 Derive the general equation…….. in a magnetic field?
Ans. As we know that
F=q(v x B)
Work done= W=F.L =q(v x B).L
Now    V=W/q =q(V x B).L /q=(v x B).L

Or       V= - vBL sinθ  b/c (cos 180=-1)

Q.14.9 What is the mechanism of ………………..loss reduced?
Ans. The electromagnetic induction is the responsible for the transfer of energy. It works on the principle of mutual induction.(Explain the process of mutual induction)

### COMMON COLLECTOR CONFIGURATION OF A TRANSISTOR

COMMON COLLECTOR CONNECTION

In  this  configuration  the  input  is  applied  between the  base  and  the  collector and  the  output  is  taken  from  the  collector  and  the  emitter.  Here  the  collector  is common to both the input and the output circuits as shown in Fig.

Common Collector Transistor Circuit

In  common  collector  configuration  the  input  current  is  the  base current  IB  and  the output current is the emitter current IE. The ratio of change in emitter current to the  change in the base current is called current amplification factor.

It is represented by

COMMON COLLECTOR CIRCUIT

A test  circuit  for determining the  static characteristic  of an NPN transistor is shown in Fig. In this circuit the collector is common to both the input and the output circuits.   To   measure   the   base   and   the   emitter   currents,   milli   ammeters   are connected in series with the base and the emitter circuits. Voltmeters are connected   across the input an…