1. 1. What are 3 things you notice in the picture. 2
1. What are 3 things you notice in the picture. 2. What are 2 things this picture makes you think about. 3. What do you think this is a picture of?

2. Video Clips Semiconductors Diodes Transistors
Diodes
Transistors

3. Semiconductors
A semiconductor is a substance that conducts an electric current better than an insulator but not as well as a conductor.
Semiconductors are used in many electronic components.

4. How Do Semiconductors Work?
The way a semiconductor conducts electric current is based on how its electrons are arranged.
Silicon (Si) is a widely used semiconductor.
When Si atoms bond, they share all of their valence electrons. There are no electrons free to make much electric current.
So, why are semiconductors such as Si used? They are used because their conductivity can be changed.
Look at picture on back!

5. Each silicon atom shares its four valence electrons with other silicon atoms.

6. Doping
You can change the conductivity of a semiconductor through doping.
Doping is the addition of an impurity to a semiconductor.
Adding the impurity (different types of atoms) changes the arrangement of electrons.
N-Type Semiconductors add atoms that have 5 valence electrons to Silicon.
P-Type Semiconductors add atoms that have 3 valence electrons to Silicon.
Look at the picture on the back!

8. Diodes
Layers of semiconductors can be put together like sandwiches to make electronic components.
Joining an N-type semiconductor with a P-type semiconductor forms a diode.
A diode is an electronic component that allows electric charge to move in one direction only.
Look at the diode diagram on the back!

10. The Flow of Electrons in Diodes
Where the two layers in a diode meet, some “extra” electrons move from the N-type layer to fill some “holes” in the P-type layer.
This change gives the N-type layer a positive charge and the P-type layer a negative charge.
If a diode is connected to a source of electrical energy, such as a battery, so that the positive terminal is closer to the P-type layer, a current is made.
If the connections are switched so that the negative terminal is closer to the P-type layer, there is no current.
Look at the picture on the back!

12. Using Diodes to Change AC to DC
Power plants send electrical energy to homes by means of alternating current (AC). But many things, such as radios, use direct current (DC).
Diodes can help change AC to DC.
Alternating current switches direction many times each second. So the diodes in an AC adapter block the current in one direction. As a result, AC is changed to DC.
Look at the picture on the back!

13. AC Adapter

14. Transistors
A transistor is an electronic component that amplifies (increases) current.
It can be used in many circuits, including an amplifier and a switch.
Transistors can be NPN or PNP transistors.
An NPN transistor has a P-type layer between two N-type layers.
A PNP transistor has an N-type layer between two P-type layers.
Look at the picture on the back!

16. Transistors as Amplifiers
A microphone does not make a current that is large enough to run a loudspeaker. But a transistor can be used in an amplifier to make a larger current.
There is a small electric current in the microphone. This current triggers the transistor to allow a larger current in the loudspeaker.
The electric current can be larger because of a large source of electrical energy in the loudspeaker side of the circuit.
Look at the picture on the back!

18. Transistors in Switches
Many electronic items use transistors in switches.
When the manual switch in the circuit is closed, a small current is made in the small loop. The small current causes the transistor to close the large loop on the right. As a result, a larger current is made in the large loop. The larger current runs the motor. You switch on a small current then the transistor switches on a larger current.
If the manual switch is opened, the circuit is broken. As a result, the transistor will switch off the current that runs the motor.
Look at the picture on the back!

20. Integrated Circuits
An integrated circuit is an entire circuit that has many components on a single semiconductor.
The parts of the circuit are made by carefully doping certain spots.
Integrated circuits and circuit boards have helped shrink electronic devices.
Because the circuits are so small, the electric charges moving through them do not have to travel very far. So devices that use integrated circuits can run at very high speeds.
Look at the picture on the back!