PHYSICS [2 Mark Question Answer]

a. 2.25 m
= 2.25 x 100 cm [As lm = 100 cm]
= 225 cm
b. 6 l
= 6 x 1000 ml [As 1 l = 1000 ml]
= 6000 ml
c. 8000 g
= 8000 ÷ 1000 kg [As 1000 g = 1 kg]
= 8 kg

(i) The base of the measuring container can be bend inwards by hammering which reduces the capacity of liquid it can hold.
(ii) Some lead can be poured into the measuring container.

A slight bend or kink in the capillary tube of the clinical thermometer near the bulb ensures that the mercury does not move back into the bulb when the thermometer is taken out of a person’s mouth for reading.

When a body to be weighed is attached to the hook, the coil is stretched downwards. The distance through which the spring gets stretched is measured by a pointer and a graduated scale attached to the spring. The reading on the scale gives the weight of the object.

Sometimes, the size of the SI unit is either too small or too big to measure a certain quantity. For example, a metre is too small a unit to measure the distance between two cities and too big a unit to measure the thickness of a wire. Hence, multiples and submultiples of units are required. Multiples are factors used to create larger forms whereas submultiples are factors used to create smaller forms of the SI units. For example, a centimetre is a submultiple and kilometre is a multiple of a metre.

The traditional units were not uniform as the length of a cubit, foot and handspan varied from person to person according to their body size. Similarly, there was no certainty that all grains were exactly the same weight. So these units could not be used.for scientific measurements where accuracy was. a prime concern. The development of a large number of systems of measurement also made it very difficult to conduct trade and commerce between different socities. Therefore, people felt the need to have standard units which could be used for accurate measurement and were accepted universally.

To measure a physical quantity, we need to compare it with a known fixed physical quantity of the same kind, i.e., a unit. Hence, the measurement of a physical quantity is always written as a combination of a numeral along with the unit. The numeral specifies the number of times the unit is repeated.

Basic physical quantities that do not depend upon other quantities are called fundamental physical quantities. There are seven fundamental quantities – length, mass, temperature, time, electric current, luminous intensity and amount of substance.

An approximation or estimation is a reasonable guess about the measure of a physical quantity. For example, -we use approximation in adding salt to food while cooking. We use approximation when we try to figure out the time it would take to reach a certain place by car. In our daily life, we use approximations in many situations. They are useful as they save time. But, since they are not accurate in measurements, they should be avoided in scientific studies and experimentation.

The degree of hotness or coldness of an object is called its temperature.
Laboratory thermometer :

• It is used to measure temperatures for scientific purposes in a laboratory.
• The kink is not present.
• The lower fixed point is -10°C and upper fixed point is 110°C
  
  Clinical thermometer:

• It is used to measure temperature of the human body.
• A slight bend or kink is present near the bulb.
• The lower fixed point is 35°C or 95° F and the upper fixed point is 42°C or 108° F.

Railways and airlines use the 24-hour clock format as they operate round the clock (24 hour). The main features of 24- hour clock system are :

• a.m. and p.m. are not used in order to avoid confusion.
• Time is shown by’4 digits. The first two digits indicate the number of hours, and the next two digits indicate the number of minutes.
• Time is expressed continuously from 00.00 (midnight) to 24:00.