H5.4 automatic circuits TV3B

• Natuurkunde
• Middelbare school
• vwo
• Leerjaar 3

5.4 Automatic circuits

Lesson goals

• Automatic circuits: sensor, switch, actuator
• How a transistor works

slidingdoors

electric kettle

Automatic circuits

Components automatic circuit

1. Sensor             Observes & produces an electrical signal (e.g.                                LDR or NTC)
2.  Switch            Responds to the sensor's signal (turns power                                on or off)
3. Actuator        Performs desired action (e.g., lamp turns on or                               alarm turns on)

Sensors

LDR (Light sensor on a lamp that comes on in the dark)

More light --> lower resistance

NTC (in a thermostat, on a cooler in the computer)

Higher temperature --> lower resistance

Transistor

can turn an actuator on/off

= an automatic switch

The transistor receives a small current at the Base, then a large current can flow from the Collector to the Emitter.

With a small current (from B to E), you can run a large current (from C to E).

Base

Tip: extra clarification look at figure 3 in your book.

a lot of light

fewer light

 tip: low light --> LDR high 

resistance

1. Why turns the light on when it's dark? 

2. Which component is the actuater in this circuit?

Summary

Automatic circuits has 3 components:

• sensor
• swichts
• actuator

Transistor is a automatic switch

• A small current flowing from the Base to the Emitter
• A large current can flow from the Collector to the Emitter

How many "legs" does the transistor have?

1. 1
2. 2
3. 3
4. 4

In the case of a burglar alarm, the alarm is the:

1. Sensor
2. Processor
3. Actuator

Homework

1 t/m 9