DC Fundamentals 1 Flashcards
2 types of common resistors?
Fixed - Resistance does not change
Variable - Not limited to one such value of resistance, may increase and decrease within certain limits
Types of fixed resistors?
- Carbon film
- Metal film
- Wire wound
- Thick film
Types of variable resistors?
- Potentiometer
- LDRs (Light dependant Resistor)
- Thermistor
Characteristics of metal film
- Designed for low power app
- Greater range of values available over carbon
- Ohmic value is represented by colours on body
- Typical tolerance of 1%
- Blue coloured body
Characteristics of wire wound
- Designed for high power app
- Limited to low range
- Ohmic value printed directly on resistor
- Typical tolerance of 10%
- Identified by rectangular ceramic casing
Characteristics of thick film resistors
- Very small size
- Designed for low power app
- Typical tolerance of 5%
- Identified by small size and lack of legs
Characteristics of potentiometer?
- 3 terminal
- Can be used as a rheostat
- R is varied by rotary or linear motion
Characteristics of DRs (Light dependant Resistor)
- Adjusts the brightness
E.g. phone screen - Read non linear
- 2 terminals
- Low R in bright light / High resitance on dull light
Characteristics of thermistor?
- PTC follow the temp - increase with increase in temp (positive)
- NTC goes opposite direction (negative)
- 2 terminals
Relationship between current and resistance?
Resistance up = current down
Types of switches
- Single pole single throw
- Single pole double throw
- Double pole double throw (mechanical latch / link)
- Rotary switches (multiple choice)
- Momentary push buttons
Relays - overview
- Not activated directly by the user
- Indirectly activated
- Beneficial in aircrafts: reduces the weight by having multiple things controlled by the one relay
- Independent to each other
- Remotely activated
Fuses - overview
- Size of wire determines how much current can flow through it
- Greater the gage of the wire, greater the current it can take
- Need to be replaced upon blowing
2 types of circuit breakers
- Toggle dial - Too much current pulls the latching mechanism down / flicking it off / breaking the circuit
- Push button -
Ohms law
V = IR
I = V / R
R = V / I
Kirchhoff’s laws
“The sum of the voltage drops in a series circuit is equal to the applied voltage.”
Va = V1 + V2 + V3
“The sum of the currents entering a node is equal to the sum of the currents leaving the
node.”
Light vs heavy load
Light load = 10 x bigger
More resistance = less current = Light load
Heavy load = less than 10 x bigger
Less resistance = more current = Heavy load
Voltage divider - overview
- Is formed when two or more components are connected in series
- Useful circuit when a lower voltage than the applied
Characteristics of carbon film resistor?
- Designed for low power app
- Wide range of values available
- Typical tolerance of 5%
- Identified by tan colour
Multimeter serviceability checks
1) Check for good physical condition and is free from damage
2) Ensure the leads are serviceable
3) Remove the black lead and put the red probe into the red port on the L - check for reading under 0.5 ohms
Components of capacitor?
- Dielectric
- Conductive plates
- Connecting leads
What is a capacitor?
- Device used to store electric charge
- 2 parallel conductive plates separated by an insulator (dielectric)
- Ideally would hold its charge forever, but realistically they leak and in turn lose potential difference
Characteristics of capacitors?
- Plate area (bigger plate area = bigger capacitance)
- Distance between plates (greater distance between plates = greater resistance = less capacity to charge)
- Dielectric constant
Explain charging capacitors?
When switch A is closed, electrons move from the negative battery terminal to the capacitor via the resistor.
At the same time, electrons move from the opposite plate of the capacitor to the positive terminal of the battery. The resulting current is referred to as the charging current
What state are the particles in the capacitor in when it is fully charged?
When the voltage across it is equal to the supply voltage
Resistor decade box
- A form of substitution box, which is used in place of a standard resistor in a circuit for testing purposes
- Contains a number of rotary
switches - Allow the user to change the resistance normally from zero ohms up to
multiple megohms
Difference between metal and carbon resistors?
Difference tolerance
Does a resistor with more or less cork screw have greater resistance?
Greater cork screw - greater resistance
Calibration check for multimeter?
- Check label is intact
- Signed
- Within date
- Text is legible
2 Types of circuit breakers?
- Toggle
- Push button
Explain how a circuit breaker works?
- Able to be reset
- Automatically switch off in the event of an excess current flowing through
- “tripped”
Does a fuse with a thicker or thinner wire hold greater amount of Amps?
Thicker fuse
In a parallel circuit, if you add more resistance - what happens to the current?
The current increases
“more lights = more need required current”
Constant value in a series circuit?
Current
Only 1 path for the current to go through, therefore this has to be current
Constant value in a parallel circuit?
Voltage
Pressure remains the same across the whole thing = voltage remains the same
REMEMBER THIS BY - Voltage divider circuit
Steps to service current probe?
1) Check physical condition - no damage
2) Check op of function button
3) Check jaws work correctly
Relationship between the plate size and the capacitance?
Relationship between the distance of the plate resistance between them?
Bigger the plate area = higher the capacitance (Directly proportional)
Greater distance between the plates = the less the resistance (inversely proportional)
