Experimental Physics

physics laboratory

Experimental work in a laboratory is an essential component of physics learning and teaching. Students often refer to experimental work in physics laboratory as ‘physics practical’. So why is physics practical important and what do you have to do in a physics laboratory?

According to renowned physicist and Nobel Prize winner, Dr R. Feynman, “the principle of science and in fact the definition of science is ‘the test of all knowledge is experiment’. Experiment is the sole judge of scientific truth”. When we observe a phenomena, we make laws that can explain that phenomena. So a falling apple is an experiment, and it has much in common with a falling ball and the ‘falling’ moon. So, “Laws of Motion” (the famous 3 laws of motion) were put forward by Isaac Newton. When a law is put forward, it must agree with experiments. In a school or college level physics experiments, we test the laws of physics and we verify that the experimental results are in accordance with the theory our textbooks teach us. We learn experimental techniques, how to work with apparatus, find errors in calculations, work within limits of accuracy and sensitivity of the apparatus. Experimental physics is not as easy as studying physics from a textbook. Students find physics difficulty for many reasons and I have written in depth on this in my other blog

So what does experimental physics involve? Experimental physics involves two types of activities: (i) student performs an experiment, (ii) student observes how a teacher performs and experiment, but student doesnot herself perform the experiment; these are the ‘demonstration experiments’. It is the first category of experiments where a student herself will perform the experiments, that interest us. The usual sequence of such experiments is:

  1. Teacher explains the aim (objective) of the experiment, setup and use of apparatus, which observations (readings) to take, how to take these observations, how to calculate a physical quantity based on these observations, precautions (DOs and DONTs).
  2. In a physics lab, you may perform experiments that involve use of heavy equipment, large currents/voltages, sharply pointed objects, mirrors or various liquids etc. Ensure that you understand how to work safely with such apparatus.
  3. Physics is a science of measurements. We measure physical quantities with instruments like a vernier caliper, micrometer screw gauge, ammeter, voltmeter, etc. Therefore, it is important to first understand how to use these measuring instruments. All measuring instruments have a ‘least count’, or the smallest measurement that can be taken with that instrument. You must also learn how to use the instrument with care so as not to cause damage to self, or to your student partners or to the instrument itself.
  4. You perform the practical, either individually or in a group of 2-3 students.
  5. Performing the practical starts with arranging the apparatus as explained by the teacher, taking observations, noting down these observations in a tabular form.
  6. Once the observations have been noted down, use the necessary formula and perform calculations to find a value that is part of the aim of the experiment. For example, a simple pendulum experiment may involve noting down the time taken for, say, 20 oscillations by varying the length of the pendulum, and then calculate the value of acceleration due to gravity (g) at that place.
  7. For analyzing the results, you may have to plot one or more graphs, hence you should be familiar with techniques to plot graphs. Plotting graphs involves knowing about: how to choose a scale, whether to keep the graph paper in portrait or landscape mode, which of the quantities to plot on X-axis, which quantity to plot on the Y-axis, labeling the axes, mentioning the scale on the top right corner of the graph paper, plotting the points and then joining these points with either a straight line or a curve. This will depend on the nature of relationship between the physical quantities – directly proportional, inversely proportional, square dependence, logarithmic dependence, etc. Remember, it is not necessary that all the readings you have taken lie on the line or graph, some of these readings may be outside the line/curve and that is OK. But most of the points will be on the graph (i.e. on the line/curve). Ofcourse, you must use only a pencil to plot a graph.
  8. Once the graph has been plotted, you may have to find (i) slope, (ii) intercepts on one or both axes, or (iii) you may have to extrapolate / interpolate and obtain another pair of readings which you have not taken. This analysis must be in accordance with the theoretical results
  9. So you can see, plotting graphs is almost an essential part of most physics experiments.
  10. It is quite possible that your experimental results do not match the exact textbook values. That is perfectly OK. Remember, we are doing an experiment, with equipment that has a limit to how accurate and sensitive it is, there can be various errors in making observations (personal errors, equipment errors, random errors such as variation in temperature or a sudden blast of wind). These errors will affect the final result. Calculate the percentage error.

So what can you do to make your trip to the physics laboratory more fulfilling and productive? Most often, the teacher will tell you in advance which practical you will be performing next week. Armed with this knowledge, you can read up the theory of that topic from your textbook, prepare questions that you can ask in the laboratory, read up on how to handle the apparatus. Be familiar with the name of the apparatus and its use in the experiment.

You can also use your time in the physics laboratory to think of alternate ways of performing the experiments, suggest improvements in techniques, discuss these with your teacher and act accordingly.

Maintain a separate lab notebook where you can record all your observations, plot graphs, show your calculations and note down the final results with experimental errors.

I usually don’t encourage students using a mobile phone in a lecture. But, I strongly recommend that students should use a mobile phone in a physics laboratory. Since the use of a mobile inside a college school/campus depends on the policies of the administration, it is extremely important that you seek the prior approval of your physics teacher or administrator before you use a mobile in the lab. So what can you do with a mobile in a lab? The most useful part is making a video recording of the experiment. You can also click pictures of the apparatus and put a caption/label to identify the apparatus. This way you can revise the experiment later on as most often physics lab work is only once or twice a week in junior classes, K12, etc.

A physics lab is a physicist’s playground. I hope you have all the fun in the lab and also learn and discover the mysteries of science.How are physics practicals performed in your school/college? Are mobile phones allowed in the lab? How do you do calculations – on a calculator or by using logarithm tables? How often do you work in the lab? Do share your views, ideas and experiences of working in the lab in the Comment section below.

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