Why does a refrigerator produce sounds periodically?            195
Can a fridge, left open in a closed room, be used to
cool the room?                                                  195
Why does it seem difficult to cycle up a steep hill than
to push the bike up at the same speed?                          196
Why does not the cycle travel backwards when we pedal
it in the reverse direction?                                    196
Automatic wrist watches stop functioning if not worn
even for a day. How does wearing them on our hand
make them function?                                             197
How do microwave ovens cook food?                               198
How does a pressure cooker work?                                198
Why does milk boil and expand so rapidly at a low
temperature though some quantity of water
is present in it?                                               199
What is Richter Scale? How is it used to measure the
severity of earthquakes?                                        201
Why do electrical appliances draw more current during
low voltage?                                                    202
Why is the earthing pin in 3 pin electrical plugs bigger
than the other two pins?                                        203
Electricity generating units based on coal and atomic
power is known to use steam turbines. But in hydroelectric
power stations water (from a dam) is made to directly
rotate the turbine and generate power. How do they
generate power from gas (fuels) fired stations?                 205
What is static electricity? Why and how is it created?          206
Why is it that neutrons have no charge?                         208
Why does high tension wires produce a humming sound?            208
How does an electric line tester glow?                          209
Why does a bird not get electrocuted on sitting on a live wire? 209
Why are fan wings slightly curved?                              210
When viewed under a tubelight, why does a table fan
appear to rotate backwards and forwards?                        211
Can we reduce power consumption by running fans
at slow speeds?                                                 212
Why do we have sodium vapour lamp in the streets and
not mercury vapour lamp?                                        212
How is white light split into seven colours when passed
through a prism?                                                213
What is the role of chokes and starters in tube lights?
Why do they make noise?                                         214
Why do street lights and head lights of vehicles look like
stars when viewed through glass?                                214
Will the life of fluorescent lamps decrease with frequent
switching on and switching off?                                 215
Why is the shadow bigger than the object?                       216
Why is it marked 6500 K on fluorescent lamps (tube light)?      216
Why does the surface of the incandescent light bulbs become
progressively greyer over time?                                 217
Is it true that gas filled lamps offer more light compared to
ordinary filament bulb for the same power input?
If yes how is it possible?                                      218
Tubelights do not give sharp shadows like filament
bulbs. Why?                                                     218
Why does the boiling point of a liquid increase with pressure?
Also why does the heat required for vapourisation decrease
and increase in the former and latter cases respectively?       219
Why do tiny bubbles coalesce? Why do they move faster near
the wall of the container and near one another?                 220
How are permanent magnets made?                                 220
Why do metallic vessels lose their initial shine after use?     222
Why is it difficult to balance a stationary two wheeler?        223
How does the speed (of vehicles) measuring device used by
the traffic police work?                                        224
How does a photocopier work?                                    225
Why is it difficult to photograph a TV picture?                 226
What is red eye reduction and its function?                     227
Why do radios receive signals well only when kept in
certain directions?                                             227
Is there any significance in using gravel on railway tracks?    228
How does audible sound pass through hard material such
as a wall and be audible on the other side?                     229
What does Dolby printed on sound systems signify?               230
Why is it possible to hear noises from far away clearly on
cool damp evenings? Is it because sound travels better
in cool, damp air than in dry air?                              230
Why do we not hear sound while sleeping or meditating?          231
Why does not sound travel in vacuum but light does?             231
Why does the flow of ink increases when pens are about to
run out of ink?                                                 232
Why do we need rods of different lengths to make
a TV antenna?                                                   232
How is it possible to transmit a number of channels through
the same cable?                                                 233
How does a thermostat work?                                     234
Why does water exhibit anomalous expansion when heated?
Why does its volume decrease until 4 degrees Centigrade
and increase thereafter?                                        236
While using a water heater coil, the water at the upper level
become warm sooner than the bottom level though we put
the coil at the bottom. Why?                                    237
What is Global Positioning System (GPS) and how
does it work?                                                   238
How do hearing aids work?                                       240
Why does boiling milk overflow but boiling water does not?      240
What is the difference between a hydrogen and an atom bomb?     241
While light from a candle illuminates a room, the gas (LPG)
flames do not. At the same time the gas stoves help cook
faster. Can any one explain?                                    242
What is infrared spectroscopy and what is it used for?          243
When we try to dissolve a granular compound (say, salt) by
stirring it in a beaker of liquid (say, water), the compound
collects in the centre of the beaker. The faster the liquid
is stirred the more rapidly the compound heads towards the
centre of the beaker. Why does this happen?.                    244
Why does a steel ball pitch higher than a rubber ball?          245
How is information stored in audio and video tapes?             246
What is the origin of gravity?                                  247
When heavy vehicles pass by the road we could feel the
floor beneath us vibrating. Some times the window
panes of nearby houses also vibrate. Can any one explain
why this is so ? Is it harmful to buildings? If so, how
can it be avoided ?                                             247
What is brake horse power (BHP)? How is it different
from the horse power (HP)?                                      249
We are all familiar with the popping ears associated with
takeoff and landing in an aeroplane. This is caused by
changes in pressure, but because the aircraft cabin is
artificially pressurised, why isn’t the internal pressure
maintained at one level throughout the journey?                 250
Why does a spinning top reverse its direction of rotation
towards the end?                                                251