My Science School

The cordless phone is an FM transmitter/receiver. The frequency range lies between 26.6 and 49.8 MHz A cordless phone essentially converts the audio signals from the telephone line into the FM waves and it is detected by the mobile handset, and vice versa. For security reasons the range is limited to about 100 metres and their power is about 500 milliwatts. Each cordless phone is assigned a particular channel (or frequency range) to avoid interference with nearby instruments. 

Cordless phone is based on wireless transmission and frequency modulation. The main components of a cordless phone are the base unit and the portable unit. While the base unit is kept at a fixed point, connected to power supply and the working telephone line, the portable unit can be carried to a certain distance, depending on the frequency range limitation. Normally in India, the permissible distance is about 100 metres.

 The base unit and the portable unit essentially consist of radio wave transmission and reception devices which enable a two way wireless communication between these units.

The radio waves are broadcast in the air through the antenna fitted to the units. Just like the signals emanating from the telephone are converted to radio frequency in the transmission side, the reverse happens in the receiver side, (i.e.) the radio frequency signals are converted into original signals, bell or speech.

 Since the handset does not have and connecting cord or wire, the name cordless phone.

            

    In normal telephone exchange systems, a pair of wires extends each telephone instrument to the telephone exchange.

Normally, copper conductors are used to give loop to indicate the exchange that the telephone hand set had been lifted for making a call or for receiving a call. In advanced countries, Optical Fibre is also used or for extending the loop.

When you make a call to your friend who is connected to another exchange, the digits are sent to the exchange to which you are connected, in the form of pulses (break and make of loop) or frequencies.

The originating exchange analyses these digits and establishes a path to the terminating exchange where your friend is connected. Over this path, signals (some of the digits dialed by you and other technical information) are sent in the form of bits or frequencies. 

The terminating exchange analyses and marks your friend's line and if it is free, a ring is sent to him and ring back tone is sent to you. When the call is answered, metering takes place.

In the cell phone system, there is no permanent wire connection between the instrument and the mobile telephone exchange. The connection between the instrument and mobile exchange is established via an intermediate station called Base Station (BS) where a transmitting tower is erected. The connectivity between the mobile exchange and the BS may be wire and between BS and Cell Phone is a Radio Channel.

The connection between a mobile exchange and another mobile exchange or public telephone exchange is by wire.

 Cell phones are technically called Mobile Station (MS) and its telephone exchange is called Mobile Switching Centre (MSC). The radio channel for both-way voice and control channel for controlling are established between BS and MS whenever required only.                                

A town or an area is divided into smaller areas called Cells. At the centre of the cell, there exists the Base Station (BS). When the MS moves around inside the cell, the signals including voice will be strong. When you use a cell phone to talk to your friend with conventional phone, you will   be connected to the BS over a booth-way Radio channel. From BS to MSC over a copper cable or Optic Fibre cable, from MSC to another Exchange and further to your friend over a copper cable

            As you are moving and when you enter into another cell, old BS reports to MSC that you have left the cell and your signals are weak. Immediately, the MSC orders all other Base stations to search for a new comer (as far as other cells are concerned, you are a new comer).

 The BS which is very near to you reports to the MSC that it has found a new corner with strong signals. The MSC orders the old BS to hand off (you) to new BS. Handing off is done in less than 400 milliseconds. But you do not feel any disturbance in your conversation. You may cross many cells during your long conversation without knowing that so many hands off have taken place. Each cell phone is associated with a unique identity stored in Subscriber Identity Module (SIM). This identity is sent to MSC through Base Station when ‘Send’ button is pressed.

The MSC analyses this and validates as to whether cell phone is authorized to make a call. If yes, the call will be put through. When there is an incoming call to the MS, first it is received by the MSC. MSC analyses the received information that contains the MS number also. This number is paged in all cells. If the MS is kept powered on, a page response is received on the control channel from the MS. A voice channel is allotted by MSC. BS and MS are ordered to tune to that channel. Once tuned through connection information is returned to the caller who gets ring-back tone. Ringing is initiated in the MS. When the MS answers, conversation can start and metering starts in MSC.

         Earth rotates from west to east causing the Sun, the Moon, stars and other planets rise from east and set in the west. On the surface of the earth each point is moving eastward with respect to an astronaut in space.

            Thus if a rocket is launched at a small angle eastward vertically the speed of earth gets added to the rocket’s speed. This reduces the amount of fuel required. If the rocket is inclined along any other direction, the speed of the earth gets subtracted from the speed of rocket and will necessitate burning of more fuel.

            In addition, in case of any failure during launch the rocket will fall back to the earth. Hence if it is launched from the east coast, the rocket will fall into the sea only. If it is launched from the west coast, in case of failure, the rocket will fall on the land endangering human habitats. Thus choosing eastward inclination is scientific but choice of eastern coast concerns safety.

            A small amount of air is trapped and pressurized when the fixed end of the thumb and the free end of the middle finger are brought together. When this pressurized air is released suddenly during the clicking it produces a sound as in the case of a balloon burst.

Sound is caused by the cracking of knuckles when a bubble which has formed in the lubricating fluid (the synovial fluid) which surrounds the two bones of the knuckles bursts.

Normally there is a lubricating fluid which prevents the two bones which forms the knuckles from grating against each other. This fluid contains tiny bubbles which cannot be seen by the naked eye.

So when the knuckle bones remain close together the fluid is under pressure and the bubbles remain tiny.

But when one clenches his fist, the bones are pulled apart which causes the bubbles to join together to form one large bubble. Then when one works the fist, the pressure changes and makes the bubble to burst which then produces a loud cracking, noise. Doctors are not sure whether cracking them is harmful or not, though there is a belief that cracking ones knuckles could make them large and unsightly.