Practice determination of focal length using :
- u – v method
- displacement method
- Practice Wheatstone Bridge setup where you are supposed to find value of an unknown resistance.
Note : The value of unknown resistance will come in the range 1.8 to 2.4 ohm.
Points to note while performing experiment:
- Ensure ‘tip to tip’ parallax removal.
- Ensure that you follow the given circuit diagram while making the circuit.
- Ensure that the DC Source is set to the voltage mentioned in the question.
- Do not keep the circuit switched ON for too long. Either switch of the DC source or remove the key.
- The polarity (i.e. positive/negative terminals) of the apparatus may not be marked in the diagram. So, ensure that your connection follows proper polarities. (e.g. if you have connected the ammeter to the circuit using a particular polarity and after switching on the circuit, the current reading shows below 0 A, then interchange the connection on the terminals of ammeter.)
- While finding null point using a galvanometer, make sure that the deflection on the galvanometer is on either side when touching the 2 ends of the given meter bridge/scale.
Points to note while recording readings:
- Record all observations up to appropriate number of decimal places depending on the least count of the measuring instrument. Like while recording from an optical bench write 30.0 cm instead of just 30 cm.
- While doing any optical experiment with lens, always record the positions of object pin, image pin and the lens and then proceed to record whatever is mentioned in the question paper.
- When using the galvanometer to find the null point length, express it up to 1 decimal place (e.g. write 68.0 cm instead of 68 cm)
- The value of a quantity or any observation must always be supported with correct units.
- Pay attention to statements like “answer correct upto 2 decimal places” or ” 4 significant figures“ and follow the instruction.
- Do not overwrite and manipulate your result.
- Record the observations neatly, in a tabular form, with proper heading and with units as per the instructions.
- Do not waste time by writing unnecessary information which is not asked like procedure, theory, diagram.
Points to note while plotting graph:
- 1st variable must be plotted on the Y axis. (e.g. if graph is ‘m’ vs ‘v’, then ‘m’ should be along the Y axis and ‘v’ along the X axis)
- Label the axes correctly with units.
- Choose uniform and convenient scale such that at least 2/3 of the graph paper is used.
- Mention the scale used in the graph clearly.
- DO NOT use KINK* along any axis. Instead shift the origin.
(*Kink is a zig-zag sign near the origin that shows that the scale interval started there, just that the numbers after it were skipped)
- Plot the points correctly [thin (.) encircled points (blob (●) is a miss plot)]
- Draw the best fit line passing through most points.
- Line should be thin and uniform covering extreme plots.
- Untouched points should be close and equally distributed on either side of the line.
- While finding slope, take two un-plotted points (i.e. not from the readings) on the best-fit line and separated from each other through a distance of more than 50% of the line drawn.
- Express slope up to the given significant figures/decimal point.
- Origin should begin from zero if the intercept is to be found.
- Co-ordinates of the origin must be given/ marked on graph paper.
- Express the final result with proper units.
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