Daily SprintSTART

1.What is a capacitor? Draw its symbol.

2.Draw a circuit diagram for a camera flash.

3.What else could a capacitor be used for?

MSA Prep

Solve:

x = 4

y = 2

3x +4y +x2 - xy

Conclusion Questions

1.    Describe something other than the examples you’ve been given that you believe uses a capacitor and its function in the device.

-

Conclusion Questions

2.    What do capacitors have to do with the dangers of older television sets?

- Older TV’s used large capacitors to operate. Those capacitors held enough charge to seriously injure someone if they touched it. The charge will remain in those capacitors long after the TV is out of use.

Transistors

Transistors

• Transistors• Parts of the Transistor• The First Transistor• Transistors as Amplifiers• Transistors as Switches• Night Light Circuit

This presentation is intended to be used with Activity 6.2.6 Transistors

TransistorsTransistor: A small electronic device used in a circuit as an amplifier or switch.

Symbol for Circuit Diagrams

Parts of the Transistor

BA

SE E

MIT

TE

R

CO

LL

EC

TO

RThe small base current controls the larger collector current.

The First Transistor

Replica

•Considered by some to be the greatest invention of the 20th century

•Invented at Bell Laboratories in 1947

•It is a crucial component in almost all modern electronic devices

•Engineers are working toward making them smaller so that more can be placed on computer chips. Many today are already smaller than a human hair.

Transistors as Amplifiers

Large load (output)

Small load (input)

Transistors as Switches

DC

1 K

5.1 K

Large Current

Load

Small Current Load

Build the circuit as shown.

When the switch is closed, you should notice that the LED in the circuit connected to the base is very dim.

But the other LED that is controlled is much brighter.

A small current amount switching on a larger current

Night Light Circuit

Challenge: Create a system with a light that comes on when it is dark, similar to a street light.

In the following circuit, will the LED be bright at day or night?

The LED will be bright during the day because brightness causes the photoresistor’s resistance to decrease.

When the resistance of the circuit decreases, more current can flow to the LED.

Night Light CircuitIn your engineering notebook, sketch the circuit shown below.

Current will always take the path of least resistance.

Use a highlighter to trace the path that current will take from the source.

Does current reach the base of the transistor?

Will current be able to reach the light?

Night Light CircuitIn your engineering notebook, sketch the circuit shown below.

In brightness the photoresistor’s resistance is low.

Use a highlighter to trace the path when there is very little resistance from the photoresistor.

Does voltage reach the base of the transistor?

Will voltage be able to reach the light?

Night Light CircuitIn your engineering notebook, sketch the circuit shown below.

In darkness the photoresistor’s resistance is high.

Use a highlighter to trace the path when there is a large amount of resistance from the photoresistor.

Trace the secondary path of resistance.

Is the voltage high enough to activate the base circuit of the transistor?

Will current be able to reach the light?

Night Light CircuitBuild the circuit as shown to test using actual components using Snap Circuits® spring sockets.

If the circuit does not work as expected, troubleshoot using the flow chart provided in Activity 6.2.6 Transistors (omit the suggestion to check solder connections).

Image Resources

Microsoft, Inc. (2009). Clip Art. Retrieved January 27, 2009, from http://office.microsoft.com/en-us/clipart/default.aspx