Sound
Introduction
A sound wave is a mechanical wave through which we listen. We can hear only a part of the mechanical wave spectrum with a frequency of 20 Hz to 20 kHz and not beyond this range. Amplitude, frequency, wavelength, and speed are some of the important attributes of a sound wave. The amplitude of sound wave determines its intensity while the frequency and wavelength multiply to give the speed of the sound wave. However, the amplitude of a sound wave in no way affects the speed of the sound wave. A simple experiment can be designed to investigate some of the attributes of a sound wave and their interrelations.
Design of Experiment
A source of sound wave capable of producing different frequencies and different amplitudes, a detector of a sound wave at a particular frequency, a measuring tape, and a stopwatch are required for this experiment. A sound wave can be then produced at different frequencies and amplitudes and the same can be detected by the detector kept at a known distance from the source. A stopwatch will be used to measure the time taken by the sound wave for traveling from the source to the detector.
Data and Results
A virtual experiment was carried out to investigate different attributes of a sound wave. The experimental data and the calculated attributes of the sound wave are presented in table 1. All the data was recorded on MS OFFICE Excel spreadsheet and all the calculations were also done using Excel only.
Table 1: Experimental data and calculated attributes of sound wave motion.
Discussion & Conclusion
Speed of sound wave using v =λ*f shows a lot of scattering. This is because what was measured is the number of complete waves and this number is small, therefore, this led to erroneous value for wavelength and finally caused a lot of scattering. However, the average value is reasonably close to the speed of sound in the air.
The value of the speed of sound calculated by the d/t method is more consistent. In this case, the error is on the account of variability in stopping the watch when the sound wave reaches the 5 m line and therefore, variability in time required to travel a fixed distance of 5 m. However, in this case, the scatter is much less. In this case, also the average is very close to the well-accepted value for the speed of sound in air.
It can be thus concluded that air is traveling in the air in this virtual experiment.
It should not be concluded that sound is traveling at different speeds. It is so that the scatter is nothing but experimental error and therefore, the average value should be taken.
Converging Lens
Introduction
A converging lens is one that converges all the light falling onto it from far away places to a point known as a focal point. Therefore, this lens is used to focus a light beam. This is essentially a convex (either biconvex or plano-convex) lens. Imaging by a converging lens can be explained using the principles of geometric optics and the lens formula, which is given below:
Lens formula 
; q is the object distance, p is the image distance and f is the focal length of the lens.
Using this formula one finds that an object kept at twice the focal distance is imaged inverted and of the same size and at equal distance from the lens but on the opposite side. The image is real. All the objects placed farther than the focal points are imaged as an inverted real image. Similarly, a virtual, straight, and magnified image is made of an object place between the lens and its focal point. No image is produced for an object placed at the focal point itself.
A simple experiment as described below can be designed to investigate the relationship between the object distance, image distance, and magnification.
Design of Experiment
A convex lens, a lens stand, an optics rail, a small pencil as an object for imaging, a measuring scale, and a screen will be required to carry out this experiment. The pencil (object) will be placed at different distances and the image will be formed. All real images will be taken on the screen and the distance of the screen from the lens will be measure. The size of the image will also be measured. All these values will be recorded and then the lens formula will be used to calculate the focal length of the lens and the magnifications produced by the lens will also be calculated.
Data and Results
A virtual experiment was carried out to investigate imaging by a converging lens the experimental data is presented in table 1 below. Table 2 presents the relevant calculated values.
Table 1: Experimental data for imaging by a converging lens.
Table 2: Calculated values for the converging lens experiment.
Discussion & Conclusion
It can be seen that some of the reciprocals of object distance (q) and image distance (p) are the same in all the trials except that there is an error in the last trial. This is because this is nothing but the inverse of the focal length of the lens which is a constant. This value is ~ 75.50 cm.
The quantity expressed by hi/ho is nothing but magnification. This physical quantity can also be calculated by p/q. As both the ratios represent the same physical quantity, therefore, the value of these ratios is always equal to each – other.
Thus it can be claimed that the experimental finding supports the hypothesis regarding the relationship between object distance, image distance, and focal length.
Electrostatics
Introduction
Electrostatics is about the electrical charges and their interaction. Electric charges are of two types – positive and negative. Like charges repel each other and unlike charges attract each other. Therefore, a positive charge repels another positive charge and attracts a negative charge and vice versa. Also, an object is normally neutral as it contains positive and negative charges in equal proportion. However, it can be made as a charged body by various processes.
One such process is charging by a battery or power source. In this case, the object acts as a capacitor. Another simple method can be the simple rubbing of two insulating bodies. In this process, one of the objects becomes electrically positive and another electrically negative. The negative charge is due to a fundamental light particle electron. During rubbing this particle is transferred to another object thus leaving behind a positively charged body. A simple experiment can be designed to study the interaction between the different kinds f charges.
Design of Experiment
A woolen cloth, two balloons one blue and another yellow, and a positively charged plate are required. The balloons will be made to interact with each other and with the woolen cloth and the positively charged plate in a variety of manners and their response will be recorded. The same will be examined to understand and make logical inferences.
Data and Results
The experiment was done in the virtual setting; following the instructions. The response was recorded against the action in a table. The experimental observation is presented in table 1 below.
Table 1: Observation table in the electrostatics experiment.
Discussion & Conclusion
Based on the observations the following charges were present on the different objects in this experiment.
That there were opposing charges on the blue balloon and the sweater can be inferred from the observation that the blue balloon got attracted towards the sweater when it was released after rubbing the sweater. Therefore, it can be concluded that after touching the blue balloon with the sweater negative charge was on the blue balloon. This is because it is easy for the negative charge to migrate from one object to another.
There is no charge on the balloon as there is no interaction between the balloon and the wall after they are brought near the wall after touching the wall.
Based on the observations of the experiment there are two kinds of charges. As the like charges repel and unlike charges attract each other and only these two interactions were observed.
The balloon sticks to the wall because of the induction effect.