### 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=Ï†/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 sinÎ¸  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)