DC Fundamentals 1

Question 1

2 types of common resistors?

Answer 1

Fixed - Resistance does not change
Variable - Not limited to one such value of resistance, may increase and decrease within certain limits

Question 2

Types of fixed resistors?

Answer 2

• Carbon film
• Metal film
• Wire wound
• Thick film

Question 3

Types of variable resistors?

Answer 3

• Potentiometer
• LDRs (Light dependant Resistor)
• Thermistor

Question 4

Characteristics of metal film

Answer 4

• 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

Question 5

Characteristics of wire wound

Answer 5

• Designed for high power app
• Limited to low range
• Ohmic value printed directly on resistor
• Typical tolerance of 10%
• Identified by rectangular ceramic casing

Question 6

Characteristics of thick film resistors

Answer 6

• Very small size
• Designed for low power app
• Typical tolerance of 5%
• Identified by small size and lack of legs

Question 7

Characteristics of potentiometer?

Answer 7

• 3 terminal
• Can be used as a rheostat
• R is varied by rotary or linear motion

Question 8

Characteristics of DRs (Light dependant Resistor)

Answer 8

• Adjusts the brightness
  E.g. phone screen
• Read non linear
• 2 terminals
• Low R in bright light / High resitance on dull light

Question 9

Characteristics of thermistor?

Answer 9

• PTC follow the temp - increase with increase in temp (positive)
• NTC goes opposite direction (negative)
• 2 terminals

Question 10

Relationship between current and resistance?

Answer 10

Resistance up = current down

Question 11

Types of switches

Answer 11

• Single pole single throw
• Single pole double throw
• Double pole double throw (mechanical latch / link)
• Rotary switches (multiple choice)
• Momentary push buttons

Question 12

Relays - overview

Answer 12

• 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

Question 13

Fuses - overview

Answer 13

• 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

Question 14

2 types of circuit breakers

Answer 14

• Toggle dial - Too much current pulls the latching mechanism down / flicking it off / breaking the circuit
• Push button -

Question 15

Ohms law

Answer 15

V = IR
I = V / R
R = V / I

Question 16

Kirchhoff’s laws

Answer 16

“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.”

Question 17

Light vs heavy load

Answer 17

Light load = 10 x bigger
More resistance = less current = Light load

Heavy load = less than 10 x bigger
Less resistance = more current = Heavy load

Question 18

Voltage divider - overview

Answer 18

• Is formed when two or more components are connected in series
• Useful circuit when a lower voltage than the applied

Question 19

Characteristics of carbon film resistor?

Answer 19

• Designed for low power app
• Wide range of values available
• Typical tolerance of 5%
• Identified by tan colour

Question 20

Multimeter serviceability checks

Answer 20

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

Question 21

Components of capacitor?

Answer 21

• Dielectric
• Conductive plates
• Connecting leads

Question 22

What is a capacitor?

Answer 22

• 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

Question 23

Characteristics of capacitors?

Answer 23

• Plate area (bigger plate area = bigger capacitance)
• Distance between plates (greater distance between plates = greater resistance = less capacity to charge)
• Dielectric constant

Question 24

Explain charging capacitors?

Answer 24

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

Question 25

What state are the particles in the capacitor in when it is fully charged?

Answer 25

When the voltage across it is equal to the supply voltage

Question 26

Resistor decade box

Answer 26

- 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

Question 27

Difference between metal and carbon resistors?

Answer 27

Difference tolerance

Question 28

Does a resistor with more or less cork screw have greater resistance?

Answer 28

Greater cork screw - greater resistance

Question 29

Calibration check for multimeter?

Answer 29

- Check label is intact - Signed - Within date - Text is legible

Question 30

2 Types of circuit breakers?

Answer 30

- Toggle - Push button

Question 31

Explain how a circuit breaker works?

Answer 31

- Able to be reset - Automatically switch off in the event of an excess current flowing through - "tripped"

Question 32

Does a fuse with a thicker or thinner wire hold greater amount of Amps?

Answer 32

Thicker fuse

Question 33

In a parallel circuit, if you add more resistance - what happens to the current?

Answer 33

The current increases "more lights = more need required current"

Question 34

Constant value in a series circuit?

Answer 34

Current Only 1 path for the current to go through, therefore this has to be current

Question 35

Constant value in a parallel circuit?

Answer 35

Voltage Pressure remains the same across the whole thing = voltage remains the same REMEMBER THIS BY - Voltage divider circuit

Question 36

Steps to service current probe?

Answer 36

1) Check physical condition - no damage 2) Check op of function button 3) Check jaws work correctly

Question 37

Relationship between the plate size and the capacitance? Relationship between the distance of the plate resistance between them?

Answer 37

Bigger the plate area = higher the capacitance (Directly proportional) Greater distance between the plates = the less the resistance (inversely proportional)