TENS 2146 Electric Devices and Measurements
Lab 3 Current and Voltage
This report was prepared by: L. Wall
Prof. R. Alba-Flores
Team Members: J. White, L. Wall
Conducted on: September 17, 2009
Submitted on : September 24, 2009
In this lab students experimented with light emitting diodes. The student built a basic circuit with two LED's and resistors in parallel. The results showed that the voltage is the same in parallel. The items that were in series had the same current. The results also showed that the current from each branch could be summed up to equal the total current from the source. The experiment also helped the student to see the voltage drop across the diode was almost the same each time. This lab showed the effects of current and voltage in a parallel circuit. This experiment also showed how the brightness was effected by changing the voltage. Equipment and materials:
• Power Supply
• Connecting wires
• A bread board
• A 330 ohm resistor
• A l k ohm resistor
• 2 Red LED's
A light-emitting diode (LED), is an electronic light source. The first LED was built in the 1925 by Oleg Vladimirovich Losev, a radio technician who noticed that diodes used in radio receivers emitted light when current was passed through them. The LED was introduced as a practical electronic component in 1962. All early devices emitted low-intensity red light, but modern LEDs are available across the visible, ultraviolet and infra red wavelengths, with very high brightness.
Figure 1. Basics Physics principle of an LED
LED's are semiconductors. They will only work if placed in the correct direction. Placing the LED in the improper direction could potentially damage it. The LED could also be damaged if it was not installed with the use of a resistor. They can not be connected directly to a power source. The anode is the positive end and the cathode is the negative end. LEDs are beneficial because they do not require much voltage to be illuminated. The LEDs are great for conservation of energy .When we subtract the LED voltage from the supply voltage it gives you the voltage that must be dropped by the dropping resistor. A decrease in voltage will result in a decrease of the brightness of the bulb .
Figure 2 shows the electrical symbol and the actual shape of an LED.
Figure 2. Electrical symbol and the actual shape of an LED
Ohms law is used to be able to calculate the current and the resistance across each of the elements in the circuit. To analyze the circuit It must be known that the voltage is the same in a parallel circuit. The current is the same in a series. The current through each branch can be added up in order to determine the current from the source. From Kirchhoff's loop law it can be determined that the sum of all of the voltage drops around a closed loop must sum to equal zero.
The objective of this lab was for the student to use their knowledge of items such as LED's, series and parallel circuit configurations, Kirchhoff's laws, and Ohm's law in order to properly analyze and solve problems with given circuit.
 Light Emitting Diodes, http://en.wikipedia.org/wiki/Light-emitting_diode
First thing we did in the lab was to create the circuit. We created the circuit by using resistors with values of Rl = 330 ohms and R2 = l k ohms and also by placing the LEDs after the Resistors so there would be no damage done to the LEDs. This s shown in figure 3.
The voltage supply was set at 8 Volts and then we tested the values for voltage and current. To measure voltage the meter has to be in Parallel with the circuit. Current is measured by placing the Multimeter in series with the circuit. In preparation for the experiment we built the circuit (shown below) using Multisim. We used simulations to get all the required measurements and used Ohm's Law (E=I*R) to solve for the rest. In the lab we set up the same circuit by connecting the...
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