 Our sense of touch is not always a reliable guide to the degree of hotness of an object.

 Temperature is a measure of the degree of hotness of an object.





 Thermometer is a device used for measuring temperatures.

 Clinical thermometer is used to measure our body temperature.



The range of this thermometer is from 35°C to 42°C. For other purposes, we use the laboratory thermometers. The range of these thermometers is usually from –10°C to 110°C.



 The normal temperature of the human body is 37°C.

 The heat flows from a body at a higher temperature to a body at a lower temperature.



 There are three ways in which heat can flow from one object to another. These are conduction, convection and radiation.



 In solids, generally, the heat is transferred by conduction. In liquids and gases the heat is transferred by convection. No medium is required for transfer of heat by radiation.



 The materials which allow heat to pass through them easily are conductors of heat.

 The materials which do not allow heat to pass through them easily are called insulators.



 Dark-coloured objects absorb radiation better than the light-coloured objects. That is the reason we feel more comfortable in light-coloured clothes in the summer.



 Woollen clothes keep us warm during winter. It is so because wool is a poor conductor of heat and it has air trapped in between the fibres.





MOTION AND TIME


 The distance moved by an object in a unit time is called its speed.

 Speed of objects help us to decide which one is moving faster than the other.





 The speed of an object is the distance travelled divided by the time taken to cover that distance. Its basic unit is metre per second (m/s).



 Periodic events are used for the measurement of time. Periodic motion of a pendulum has been used to make clocks and watches.



 Motion of objects can be presented in pictorial form by their distance-time graphs.

 The distance-time graph for the motion of an object moving with a constant speed is a straight line.





ELECTRIC CURRENT AND ITS EFFECTS




 In the bulb there is a thin wire, called the filament, which glows when an electric current passes through it.





 When the bulb gets fused, its filament is broken.


 An electric bulb is used for light but it also gives heat. This is not desirable.






 This results in the wastage of electricity. This wastage can be reduced by using fluorescent tube lights in place of the bulbs.


 Compact fluorescent lamps (CFLs) also reduce wastage and can be fixed in the ordinary bulb holders.





 These days Miniature circuit breakers (MCBs) are increasingly being used in place of fuses.


 These are switches which automatically turn off when current in a circuit exceeds the safe limit.





 The coil in the above activity behaves like a magnet when electric current flows through it. When the electric current is switched off, the coil generally loses its magnetism.


 Such coils are called electromagnets. The electromagnets can be made very strong and can lift very heavy loads. The coil is no longer an electromagnet.





 It no longer attracts the iron strip.


 The iron strip comes back to its original position and touches the contact screw again.