Basic Laboratory Instrument – Lab Report Example
Basic Lab Instrument Familiarity and Resistor Basics Objectives To achieve basic laboratory instrumental familiarity.
2. To understand how to work with resistors and application of Ohms Law.
Resistance is the opposition offered to the flow of charge. Electrical resistance in measured in Ohms, which is the resistance of the conductor in which the current is 1 ampere flows when a voltage of 1 Volt is applied across a conductor (Duncan and Heather 12). For resistors in series, the same current flows each of the resistors whereas the total sum of the voltage across each resistor equals to the total voltage applied. Therefore, the combined resistance is given by
For resistors connected in parallel then the equivalent resistance is given by equation 4 below
In many electrical circuits, it is important to determine the rate at which electrical energy is transferred into other forms of energy. To calculate power P for electrical appliances, we find the product of the current (A) through it and the Potential difference (V) across it. Thus,
Various laboratory apparatus were provided including the Power supply(PSU), Digital Multimeter (DMM), Digital Storage Oscilloscope (DSO) and color coded the resistor. The current limit facility, the kelvin connection split power supply system in PSU, were carefully studied and provided basics of understanding the laboratory uses of a Power Supply Unit. Simple DC voltages in DMM were investigated, and measurement of resistance using a DMM was equally demonstrated.
The DSO was configured to read DC volts. The Power Supply Unit was connected to the input of the DSO to demonstrate how it is useful in determining Voltages. The DSO was configured to measure two separate DC voltages simultaneously.
Small axial- leaded resistors were provided and using the resistor color code Figure 1 in the appendix was used to identify the resistors. The total equivalent resistance for two resistors chosen at random was calculated using equation (1) in the introduction. The two resistors were then connected in series using breadboards provided, and the equivalent resistance was measured using a DMM. Similarly, the equivalent resistance for the two resistors connected in parallel was calculated using equation (2). The two resistors were then connected in parallel using the breadboard and their total resistance determined using a DMM.
A potential divider that produced 5V output from a 12V input was made and designed in a way that the circuit drew 10mA from the 12V supply when no load was connected. The circuit diagram is as shown in figure 2 in the appendix.
A potential divider from two 1Mega ohm resistors was connected to 12V DC, and the output was predicted. The output voltage was measured using a digital Multimeter and then repeated using the oscilloscope. The values were recorded and interpreted in the results below. Using the resistor power ratings for the resistors provided, the maximum voltage applied across each resistor was determined.
Results and Discussion
Using equation 1 in the introduction the theoretical resistance can be evaluated as follows.
R = (2200 + 2200) Ohms
Using the Digital Multimeter the effective resistance for the series circuit connection was recorded to 4373 Ohms. This resistance is approximately equal to the above theoretically calculated resistance. The difference in resistance could be due to the manufacturer’s errors that cannot be avoided in the manufacturing process among other factors.
Similarly using equation 2 in the introduction the theoretical resistance can be calculated to be
In a similar way, the parallel resistance obtained from the breadboard parallel circuit connection was RT=1093 Ohms, which approximately equal to the theoretical effective resistance calculated.
The potential divider circuit diagram is as shown in figure 2 in the appendix. It was found out that for an output of 5V from 12V with a current of 10mA a load resistance of 1700 Ohms and 500 Ohms were connected as shown in the Figure 2.
When the resistance across the output varies the output voltage equally varies giving a circuit that in one way resembles a sensor subsystem that like the dark sensor that is used to switch on the light automatically in the evening.
Incase of load resistance variation a shunt resistor is usually connected across the output to act as a voltage regulator.
A potential divider was made for 1M ohm resistors in which the output voltage of 6V was obtained from the 12V DC supply. The actual readings using the DMM and oscilloscope were at a variance because of the operational parameters of each equipment.
The maximum Voltage that can be applied across each resistor was calculated using equation 3 in the introduction as follows
For the 1M ohm resistor was calculated using equation 4 as shown
The voltage rating is higher than the one calculated because of different load resistances.
Understanding the operation of circuits plays an important role in electronics. Some features of circuits cannot well be understood without having a foundational hands on experience and knowledge using laboratory apparatus. Proper reading of resistor color coding is also important in electronics as well as their properties including power ratings. Notably, the calculated theoretical values do not necessarily reflect the actual values obtained practically. This is due to variations that originate from the equipment used and errors that cannot be evaded by the manufacturer of the equipment.
Heather K. and Duncan K. and GCSE Physics, 4th Ed. Book print S.L: Barcelona, Spain, 2001. Print.
Fig 1. Resistor
Fig. 2 Potential divider