CHAPTER 18: D. C Circuits
 Ohm’s Law – states that the current passing through a conductor is directly proportional to the
potential difference across it, provided that the physical conditions (like temperature) is constant
Current
Voltage
Resistance
Series Circuits
IT=I1=I2=I3…
VT=V1+V2+V3…
RT=R1+R2+R3…
Parallel Circuits
IT=I1+I2+I3…
VT=V1=V2=V3…
RT=R1=R2=R3…
1. POTENTIAL DIVIDERS
- Line of resistors connected in a series to provide a fraction of the voltage of source to another part
of the circuit
2. VARIABLE POTENTIAL DIVIDERS
- Potential dividers used to vary the output voltage
a. Rheostat – variable resistor that is connected at two terminals
b. Potentiometer – variable resistor that is connected at three terminals
3. INPUT TRANSDUCERS
- Converts non-electrical energy to electrical energy
- Examples: microphone (sound – electrical), photocells ( light- electrical),
thermocouple (heat – electrical) and pressure sensor (pressure – electrical)
a. Thermistors
- Resistors whose resistance varies with the temperature.
- The higher the temperature, the lower the resistance, the higher Vout
- Knowing Vout can also determined the temperature
b.
-
LDR (Light Dependent Resistors)
Resistors whose resistance varies with the amount of light
The brighter the light, the lower the resistance, the higher the Vout
Commonly used in automatic street lights