Spherometer

- Spherometer
- Glass strip
- Concave surface
- Plane glass slab
- Glass strip
- A sheet of paper
- A ruler
- Pencil

- Raise the central screw of the spherometer and press the spectrometer gently on a sheet of paper so as to get the pin pricks of the three legs. Mark these pricks as A, B and C.
- Measure the distance between the pricks by joining the points as to form a triangle.
- Note these distances (AB, BC, and AC) on the paper and take their mean as l.

- Note one pitch scale division on the pitch scale or vertical scale.
- Take 5 full rotations on the central screw.
- Measure the distance moved by the screw.
- Hence, Pitch = Distance moved /number of full rotations.
- Then

- Raise the screw sufficiently upwards.
- Place the spherometer on the concave surface so that its three legs rest on it.
- Gently turn the screw downwards till the screw tip just touches the concave surface.
- Note the reading of the circular disc scale which is in line with the vertical (pitch) scale. Note this reading as 'a', which will act as reference.
- Remove the spherometer from over the concave surface and place it over a large size glass slab.
- Turn the screw down wards and count the number of complete rotations made by the disc (one rotation becomes complete when the reference reading crosses past the pitch scale.)
- Continue till the tip of the screw just touches the plane surface of the glass slab.
- Note the reading of the circular scale which is finally in line with the vertical (pitch) scale. Note this reading as 'b'.
- Find the number of circular (disc) scale division in the last incomplete rotation.
- Now find total reading using the relation equation 1.
- Repeat steps 3 to 9, three times .Record the observation in tabular form.
- Calculate the radius of curvature of the given concave surface using the equation 2.

- Raise the screw sufficiently upwards.
- Place the spherometer on the glass strip so that it rests between its three legs.
- Repeat the above steps 3 to 9, three times .Record the observation in a tabular form.
- Find total reading using the relation equation 1.

- Click on the object shown on the left hand menu, to measure its thickness
- Tighten the screw by clicking on the respective arrows (left / right) on the screw, until it touches the object.
- Note the reading on pitch scale, the circular disc and note it down as the reference variable.
- Again click on the object on the left hand menu to remove it from under the spherometer.
- Tighten the screw by clicking on the respective arrows (left / right) on the screw, until it touches the glass slab.
- Note down the complete rotations on the pitch scale and note the reading on circular disc for fractional rotation.
- Based on the selected object;
- Calculate the radius of curvature if it is the spherical surface using the equation 2.
- calculate the thickness it it is the glass strip using the equation 1.

- Note down the reading in the text box.
- Click on the check button to find if the answer is correct.
- To redo the experiment, click on the 'Reset' button.

In triangle ABC marked by the legs of the spherometer

AB = ------cm

BC = ------cm

AC = ------cm

Mean value of l is, = ----cm

1 pitch scale division = 1mm

Number of full rotations given to screw = 5

Distance moved by the screw=5mm

Hence pitch,

Number of divisions on circular scale = 100

Hence least count=

Object placed | Circular scale reading | No of complete rotation on plane glass sheet(n) | No of disc scale divisions in incomplete rotation X=(a-b) or (100+a)-b | Total reading = (n x p) +(x x l.c)mm | |

On concave surface(initial) | On plane glass sheet(final) | ||||

Glass strip | t = | ||||

Concave surface | h = | ||||

The thickness of the glass plate, t = --------------- mm = --------------------m .

Mean value of h = -----------------------mm.

Radius of curvature of the spherical surface = ---------------cm=................m

The thickness of glass strip = ------------m

The radius of curvature of the given concavesurface = -----------------m

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