One Way Current Flow - Northern Ontario Wires Inc. way current.pdf · One Way Current Flow Topic ... *A breadboard is a device that allows temporary connections to be made ... It

© Diagram Visual Information Ltd. Published by Facts On File, Inc. All electronic storage, reproduction,or transmittal is copyright protected by the publisher.

One Way Current Flow

TopicSimple electronic circuits

IntroductionElectronics can be defined as the study and design of systems using the flow ofelectrons through components such as semiconductors, resistors, and capacitors.It uses many of the concepts underlying electric circuits, but many of thecomponents used in electronic circuits have specialized characteristics. Forinstance, a diode (whose name refers to the fact that it has two electrodes, ananode and a cathode) is a component that allows electrons to flow around acircuit in one direction only (see diagram 1 below). In this experiment, you willuse light emitting diodes (LEDs) to demonstrate that diodes only allow current toflow in one direction. An LED (see diagram 2 below) is a special type of diodethat lights up when current flows through it; the color of the LED depends onthe material used to make it. In this experiment, you will also construct a simpleelectronic circuit to find out more about the properties of LEDs.

Current flow in a diode

Selection of light emitting diodes (LEDs)

Time required15 minutes for Part A10 minutes for Part B

Materials9 volt battery and snap connector clip leads or other suitable connection5 mm (0.2 in.) green LED system (e.g. breadboard*)560 ohm resistor (0.25 watts) clock or watch

1 anode cathode

current allowed this way

+ –

2

© Diagram Visual Information Ltd. Published by Facts On File, Inc. All electronic storage, reproduction,or transmittal is copyright protected by the publisher.

*A breadboard is a device that allows temporary connections to be madebetween electronic components. It consists of a plastic block with holes throughwhich the wires from the components are inserted. Beneath each hole is a clip,which holds the wire in place and makes electrical contact with othercomponents. The breadboard shown in the experiments in this section has twocentral blocks where connections are made along each horizontal row and twolines down each side in which connections are made down the vertical rows.

If you are using a breadboard, you will also need a short length of connectingwire (e.g., approximately no. 20 gauge, insulated, tinned copper wire with about0.5 cm of insulation stripped away at each end).

Electronic components are available from suppliers such as RadioShack(http://www.radioshack.com). The appearance of the components may varyamong suppliers. Simple wiring diagrams and circuit diagrams are given in thisexperiment to show the arrangement of the components. Diagram 3 belowshows the symbols used in the circuit diagrams in this experiment.

Symbols used in circuit diagrams

ProcedurePart A: Current flow and LEDs1. Look at the LED. It has a plastic body with two wires coming out of it; these

are the electrodes. The wires may be different lengths; if so, the shorter wire isthe cathode. If the LED has a flat side, this should be on the cathode side.Identify the anode and the cathode of your LED.

2. Set up the equipment as shown in diagram 4 on the next page (i.e., anode ofthe LED connected to the positive supply voltage). Observe the LED andrecord your observations in data table A on the next page.

3. Disconnect the LED and reverse the connections (i.e., cathode connected tothe positive supply voltage). Observe the LED and record your observations.Disconnect the battery from the circuit.

resistor LED supply voltage(longer line identifies positive pole)

3

Safety noteDo not use an electrical outlet.

© Diagram Visual Information Ltd. Published by Facts On File, Inc. All electronic storage, reproduction,or transmittal is copyright protected by the publisher.

Circuit diagram (A) and wiring diagram (B) for Part A

Part B: Sensitivity of componentsWarning: make sure your teacher knows you are doing this experiment, as it willmake the LED unusable.

1. Set up the equipment as shown in diagram 5 below (anode connected to thepositive supply voltage).

2. Observe the LED for about 5 minutes and then disconnect the circuit. Gentlytouch the LED. Record your observations in the first row of data table B onthe next page.

3. Reconnect the same LED in the circuit. Observe and touch the LED. Recordyour observations in the second row of data table B on the next page.Disconnect the battery from the circuit.

Circuit diagram (A) and wiring diagram (B) for Part B

4A 4Bbattery

connecting wire

560 ohmresistor

LED

breadboard

9 volt

DATA TABLE AObservations

Appearance of LED

Appearance of LED withconnections reversed

5A 5Bbattery

connecting wire

LED

breadboard

9 volt

© Diagram Visual Information Ltd. Published by Facts On File, Inc. All electronic storage, reproduction,or transmittal is copyright protected by the publisher.

AnalysisPart A: Current flow and LEDs1. What was the appearance of the LED when the circuit was connected as

shown in diagram 4?2. What was the appearance of the LED when the connections were reversed?

Part B: Sensitivity of components1. What was the appearance of the LED when the circuit was connected as

shown in diagram 5? 2 How did the LED feel when you touched it after it had been disconnected

from the circuit in step 2?3. What was the appearance of the LED after the circuit had been reconnected in

step 3?

Want to know more?Click here to view our findings.

DATA TABLE BGlowing? Color (if glowing) Temperature

Color and condition of LED (step 2)

Condition of LED (step 3)

5. When the magnet is stationary, no current is recorded. 6. When the magnet is moving quickly in and out of the coil, there is a larger

reading on the meter than when it is moving slowly. These results follow partof Faraday’s law of induction, which relates the speed with which a magnetmoves relative to a conductor to the size of the induced current.

8.07 Electric Motor Construction1. The motor spins in the opposite direction when the poles of the magnets are

reversed.2. The motor spins in the opposite direction when the connections to the cells are

reversed.

Electricity flows through the coil when the wire from one end of the coil is incontact with one of the brushes, and the wire from other end of the coil is incontact with the other. As the coil is in a magnetic field, a force acts on it(force on an electrical conductor in a magnetic field) and it moves round onthe axle, breaking the electrical connection. The wire from the other side ofthe commutator now touches the brush and current flows through the coilagain; the force acts on it again and the coil continues to rotate. The effect ofthese events is to cause the coil to continue turning as the circuit for thecurrent to flow through the coil is continually made and broken.

The direction of rotation is reversed if the magnetic field is reversed (it actsnorth to south) following Fleming’s Left Hand Rule (see Experiment 8.05:Invisible Force). If the direction of the electric current flow is reversed, thedirection of rotation is also reversed.

Electronics9.01 One Way Current Flow

Part A: Current flow and LEDs1. The LED glowed green when the circuit was connected as shown in

diagram 4. 2. The LED did not glow when the circuit was connected with the LED the other

way around.

A semiconductor diode is a silicon or germanium crystal of which part (p-type) has been treated so that it has excess positive charges; the other part (n-type) has been treated to have an excess of electrons. If a cell is connectedacross such a diode, electrons will flow as indicated in the diagram on the nextpage. Virtually no current flows if the semiconductor diode is connected theother way around (the diode is said to be “reverse biased” in this situation),unless a very large voltage is used and the diode breaks down.

PHYSICS EXPERIMENTS ON FILETM10.41 • OUR FINDINGS

© Diagram Visual Information Ltd. Published by Facts On File, Inc. All electronic storage, reproduction,or transmittal is copyright protected by the publisher.

PHYSICS EXPERIMENTS ON FILETM OUR FINDINGS • 10.42

© Diagram Visual Information Ltd. Published by Facts On File, Inc. All electronic storage, reproduction,or transmittal is copyright protected by the publisher.

p-type n-type

many excesspositivecharges

manyelectrons

junctionappreciable

current

Electron flow through a diode

Part B: Sensitivity of components1. The LED glowed yellow, then orange. It then began to glow less brightly. This

shows that the current through the LED was greater than it was designed totake (this is usually 10 mA).

2. The LED felt hot. This shows that the LED was overheating.3. Our LED did not glow, showing that it had been destroyed and was no longer

capable of conducting. It is important to protect electronic components suchas LEDs by connecting them in series with a resistor.

Many examples of output devices (LED, buzzer, motor) can be incorporated inelectronic circuits. As in electrical circuits, they can be connected in series or inparallel.

When studying electronic circuits, it is important to bear in mind the idea of thepositive and negative supply rails – the points in the circuit that notionallysupply and return the electric current (see the diagram below left). Circuit diagrams in electronics are often complicated so, to simplify them, thesupply is often not shown. The positive supply rail is then drawn as a line, whichrepresents the positive side of the circuit. Another line is drawn representing thenegative side and is shown at 0 volts (see the diagram below right).

Positive and negative supply rails Example circuit diagram for electronics circuit

negative supply rail

positive supply rail+ 9 V

0 V 0 V

+ 9 V