Working Of Stop Watch

Q.27: Write down working of a Stop Watch?


It is a special watch to measure time interval for an events.


In normal condition both the hands remain static and indicate zero reading on their dials.

  • To note the time both hands of the stop watch are set at zero by pressing and releasing the knob B.
  • As the knob B is pressed and again Stop Watch released the watch starts.
  • When the second’s hand completes one rotation of sixty seconds the minutes hand advances by one division.
  • When we want to stop the watch the knob B is pressed and released again.
  • The new position of the hands gives the time interval for which the stop watch was in operation.

Q.28: What is a measuring cylinder?


it is a glass cylinder with a scale graduated in cubic centimeter (cm3) or millilitres (ml). It is used to find the volume of liquids.

When a liquid is poured in it, the liquid level rises to certain height in the cylinder. The level of liquid in the cylinder is noted and the volume of the liquid is obtained.

We should keep the eye at level with the bottom of the meniscus of the liquid surface. Cylinder must be on a smooth horizontal table.

Q.29: Define error? Write down its types?


An error is defined as the difference between the measurement and the actual value.


Personal Error:

Personal error is the error that belongs to the person who is performing the experiment. It may arise due to making an error in reading a scale.

In order to record a reading from a scale we have to line up the object we are measuring with the scale and hold our eye in one particular position for making a correct observation. Personal error is minimized by taking some careful precautions or by adopting some proper procedure.

Random Error:

A random error can arise due to external condition e.g. the temperature, moisture or voitage may fluctuate. Such error can be minimized by taking several reading and calculating the mean value.

Systematic Error:

This error arises due to a fault in a measuring instrument. It might be due to a systematic variation and is called zero error. This might also arises due to non – uniform or wrongly marked graduation. We can remove the error by comparing the measuring instrument with a standard instrument. We can also make the zero correction whether it is positive or negative.

Q.30: What is accuracy? How can we ensure accuracy?


It is the measurement of a quantity as also to the factual or real values as possible. We can increase the accuracy of a measurement by controlling and reducing all types of errors.

Ensuring Accuracy:

An easy way of ensuring accuracy is to take a large number of reading of the same measurement and take their average as given below:

The average or mean value of the set of numbers 5.42, 6.18, 5.70, 6.01, 6.32


Mean = 5.42 + 6.18 + 5.70 + 6.01 + 6.32


Mean = 5.93

Here the lowest value is 5.42 and the highest value is 6.32, the deviation between these values is 0.9. But the deviation of the individual numbers from the mean or average value is less then 0.90. Thus the average value is considered close to the real value.