### How weightlessness experiment in a satellite overcome? Give relevant formula

In order to produce an artificial gravity in the space craft, the laboratory of space craft is rotated with suitable frequency about its own axis. The rotation is so maintained that the astronaut do not feel weightlessness. The frequency of rotation depends on the length of laboratory of space craft.

FREQUENCY OF ROTATION

Consider a space craft whose laboratory is 'L' meter long consisting of two chambers connected by a tunnel. Let us see how many revloutions per second must the space craft make in order to supply artificial gravity for the astronauts.
Let 'T' be the time for one revolution and 'f' be the frequency of rotation.

R = L / 2 --------(i)
When the laboratory revolves, a centripetal force is experienced by the astronauts.

Fc = mv2/r --------(ii)
According to Newton's second law of motion

Fc = mac --------(iii)
Comparing equations (ii) and (iii)

mac = mv2/r
or
ac = v2/r
Where ac is the centripetal acceleration
Since radius of laboratory is R , therefore,

ac = v2/R --------(iv)
Now we will determine the linear speed of the laboratory.
In one rotation of the laboratory
Distance = 2pR
time = T
velocity = ?
Using the relation        s = vt
2pR = vT
or
v = 2pR/T
Putting the value of v in equation (iv), we get,

ac = (2pR/T)2/R

ac = (4p2R2/T2)/R
ac = (4p2R/T2)
ac = 4p2R x 1/T2
But 1/T = frequency (f)
Therefore,

ac = 4p2R x f2
f2 = ac/4p2R

For natural gravity acceleration must be equal to 9.8m/s2 i.e. ac = g , thus

This expression indicates that the frequency of rotation depends on the length of the laboratory of space craft. Larger is the laboratory, smaller should be the number of rotation per second to obtain the natural gravity effect.

### 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…