Length – Meter ruler , Vernier caliper , Micrometer screw guage , Spectrometer , Travelling microscope

Mass – Electronic balance , Triple beam balance

Time – Stop watch , Digital clock

      Least count

• It is the least value of physical quantity which can be measured using a measuring instrument.

Vernier caliper

Internal jaws – for measuring inner dimensions

External jaws – for measuring outer dimensions

Depth bar – for measuring depths

Least count = 0.1 mm

Reading =main scale reading + vernier scale coincide × least count = 100+2×0.1=100.2 mm

Zero error and correction

The instrument is said to have  if the zero of the main scale doesn’t coincide with the zero of the vernier scale when the two jaws of vernier caliper are brought into contact.

Zero error = 0.3 mm

Correction = -0.3 mm

Zero error = 0.8 mm

Correction = +0.8 mm

Micrometer screw guage

Pitch – It is the linear distance moved by thimble along the main scale when the thimble is given one rotation.

Least count =  Pitch/Number of divisions in the circular scale

Main scale –  0.5 mm divisions                  Least count=0.01mm

Reading = 2.5 + 38 ×0.01 = 2.88 mm

Zero error and correction

Spherometer

Pitch = It’s the linear distance moved along main scale when circular scale is given one completed                             rotation.

Least count = Pitch/Number of divisions in the circular scale.thDetermination of the radius of curvature of a spherical surface

• Take a plain glass block and keep the spherometer on it and turn the screw until tip of the screw just touch the glass block and take the reading(h₁)
• Then keep the curved surface on the glass block
• Keep the spherometer on the curved surface and turn the screw until it just touch the curved surface and take the reading(h₂)
• The height moved by the screw h = h₂-h₁

R = a²/6h + h/2

a = distance between two legs

Travelling microscope

The principle component of a travelling microscope is it’s microscope. It enlarges the diameter so measurement can be done easily.

To find the internal diameter of the capillary tube 

• Place the capillary tube horizontally on the adjustable stand.
• Focus the microscope on the end dipped in water.
• Make the horizontal cross- wire touch the inner circle at A (fig i). Note microscope reading on the vertical scale.
• Raise the microscope to make the horizontal cross wire touch the circle at B (fig ii). Note the vertical scale reading.
• The difference between the two readings will give the vertical internal diameter (AB) of the tube.
• Move the microscope on the horizontal scale and make the vertical cross wire touch the inner circle at C (fig iii). Note microscope reading on the horizontal scale.
• Move the microscope to the right to make the vertical cross wire touch the circle at D  (fig iv). Note the horizontal scale reading.
• The difference between the two readings will give the horizontal internal diameter (CD) of the tube.

• We can calculate the diameter of the tube by calculating the mean of the vertical and horizontal internal diameters. Half of the diameter will give the radius of the capillary tube.