LAB 2: Circuitos de Corriente Directa (DC) PARTE I OBJECTIVES

Transcripción

1 LAB : Circuitos de Corriente Directa (DC) PARTE I OBJECTIVES To learn to design and construct simple circuits using batteries, bulbs, wires and switches. To draw circuit diagrams using symbols To understand the measurement of current and voltage using microcomputerbased probes OVERVIEW In the following lab you are going to discover and extend theories about electric charge and potential difference (voltage) and apply them to electric circuits. You will use a battery, a device that generates an electric potential difference (voltage) from other forms of energy. The type of battery you will use is called a chemical battery because it converts internal chemical energy into electrical energy. Alternatively you could also use the DC power supply that comes with the instrumentation. As a result of a potential difference, electric charge is repelled from one terminal of the battery and attracted to the other. However, no charge can flow out of the battery unless there is a conducting material connected between the two terminals. If a light bulb is connected between the two terminals of the battery, the flow of charge will cause the light bulb to glow. In this lab, you are going to explore how charge flows in wires and bulbs when energy has been transferred to it by a battery. You will be asked to draw circuit diagrams and use microcomputer-based probes to measure and graph voltages and current as a function of time. ACTIVITY : Using a battery, one wire and one bulb connect the wire and the bulb to the battery so as to cause the bulb to glow. There are two arrangements that work and two that do not work. Draw circuit diagrams for the arrangements that work.

2 ACTIVITY : You will now explore models for current in a circuit. Use any one of the arrangements above. Which of the following models you think best describes the flow of current in the circuit. Model A: There is an electric current from the top terminal of the battery to the bulb through wire, but no current back to the base of the battery through wire, since the current is used up in lightning the bulb. Model B: There is an electric current in both wires and in a direction from the battery to the bulb. Model C: The electric current is in the direction shown, but there is less current in the return wire (wire ), since some of the current is used up in lighting the bulb. Model D: The electric current is in the direction shown, and the magnitude of the current is the same in both wires and.

3 ACTIVITY 3: Measuring potential difference (voltage) and current in a circuit consisting of a battery, a switch and a bulb. You will be asked to use the current sensor and the voltage sensor for this purpose. You must remember that the current sensor is always connected in series with the bulb through which you wish to measure the current and the voltage sensor is always connected in parallel across the bulb to measure the voltage. Switch Voltage Sensor Curre nt Sensor With the circuit connect as shown in the figure, plot graphs of voltage as a function of time and current as a function of time. Keep opening and closing the switch in order to study its effect on the current and voltage that you are measuring. What do you conclude? 3

4 ACTIVITY 4: Repeat activity 3 but with two bulbs connected to the same battery. Draw the circuit diagram and proceed to measure the current through each bulb (use two current sensors if you wish) and the voltage across the battery. What do you conclude? 4

5 PARTE II Propósito: Los Circuitos proveen la base para toda la electrónica de instrumentación. En este laboratorio, tendremos la experiencia en construir circuitos, midiendo la diferencia en potencial a través de los resistores y la corriente que fluye a través del circuito. Introducción Los resistores son componentes que tienen un valor de resistencia al flujo de corriente que puede ser utilizado para bajar el potencial o la misma corriente. Por la ley de Ohm, el voltaje a través de un resistor es directamente proporcional a la corriente que pasa por este. V = IR () Donde V es el Voltaje que se mide en Julios/Columbios, I es la corriente a través del resistor que es medida en Columbios/segundos que es la definición para un Amperio (A) y R es el valor de la resistencia medida en ohmios (Ω). Cuando los circuitos son conectados en serie, como lo muestra el circuito ilustrado en la figura. Por la ley de Kirchhoff s que nos dice que la suma de los voltajes a través de una malla son igual a cero. R I V R Figura. Circuito DC en Serie Entonces por el diagrama anterior podemos decir que la corriente es la misma para todo el circuito, y que la suma de los voltajes en los resistores debe ser igual al voltaje de la fuente tal como lo ilustran la ecuaciones y 3. V = V + V () R R V = IR + IR (3) Cuando los resistor son puestos en paralelo, como el circuito que se muestra en la figura. la caída en potencial para cada resistor es la misma y la corriente se dividen entre los 5

6 resistores. El valor de la corriente fluyendo por cada resistor es el voltaje aplicado dividido por el valor de la resistencia. V = V = V (4) R R I = I+ I (5) V VR VR R R R (6) eff = + (7) R eff R R V R R Figura. Circuito DC en Paralelo Procedimiento: Examine los resitores examines las banda de colores para saber que valores tienen los resistores. Ensamble los circuitos tal y como lo ilustran las figuras 3 y 4, coloque los sensores de voltaje y corriente suplidos por el instructor. Ejecute el programa Data Studio para poder capturar la data recogida por los sensores, luego llene la sección de datos ilustrada adelante. 6

7 R R V R3 kohm Figura 3. Ciruito DC en Serie V R R R3 Figura 4. Circuito DC es Paralelo Reporte de Laboratorio A. Resistores en Serie Valores los resistores R R R 3 Fuente de Voltaje V Resistencia Equivalente R e Corriente I Caida de Voltaje a traves de los resistores 7

8 V R V R V R3 Medidas Experimentales I I I I 3 B. Resistores en Paralelo Fuente de Voltaje V Resistencia Equivalente R e Corriente I Corriente a través de los resistores I I I 3 8